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C0NQ.140.297

MODULAR AUTOMATIC VOLTAGE REGULATOR

GENERAL PRINCIPLE, OPERATION

AND

MAINTENANCE INSTRUCTION

NANJING TURBINE & ELECTRIC MACHINERY (GROUP) CO., LTD.

NANJING CHINA

MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297

2�

CONTENTS

SECTION TITLE PAGE

1 INTRODUCTION 3

2 MAVR UNIT

4

3 MAINFRAME

9

4 CONTROL CARD 39

5 AUTO POWER CARD 82

6 EXCITATION LIMITER CARD 86

7 POWER FACTOR CONTROL CARD 97

8 EXCITATION MONITOR CARD 114

9 VOLTAGE MONITOR CARD 140

10 MAVR AUXILIARY RACK 156

11 COMMISSIONING 184

12 FAULT FINDING 186

13 INSTALLATION AND MAINTENANCE 195

14 OPERATION 199


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1. INTRODUCTION

The 'Modular Automatic Voltage Regulator' (MAVR) is designed to

control the excitation of large brushless or statically excited generators.

They are housed in two rack assemblies, named MAVR unit and the

auxiliary rack with external dimensions of 409.5 × 496 × 177 and 365 ×

488 × 266 respectively. MAVR unit has the advantages of a compact

modular construction, enabling a wide range of optional features to be

readily incorporated into the excitation system.

The basic unit for use with brushless generators incorporates the

following plug in modules: auto control bridge; control card (which

includes over flux limiter, diode failure detector and fast acting current

limiter); and excitation limiter card (which includes over and under

excitation limiters). An electronic manual control system in the MAVR

auxiliary rack is used. When used with a statically excited generator,

manual and auto circuits used on a brushless generator are omitted and

the control signal from the static control card is routed to an external

thyristor converter.

The motorized voltage setting potentiometer is incorporated on the

front fixed panel of MAVR unit, which is suitable for manual or remote

operation.

Optional extras include the excitation bias or power factor control

cards, both of which can be used to control power factor or reactive

current. For use on twin AVR systems voltage and excitation monitors

to initiate AVR change-over are also available.

Connections to the unit are via plugs and sockets at the rear of the

rack to facilitate easy removal of the AVR. The outgoing sockets are

connected to multicore cables which require termination in the


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excitation panel.


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2 MAVR UNIT

2.1 The MAVR unit comprises the mainframe which carries

certain fixed components and into which are plugged various

withdrawable cards.

The mainframe forms the necessary interconnections between the

component parts of the MAVR and provides the required isolation of

input signals. Also included are the power supply components, output

relays and outgoing plug connections. These components are mounted

on two printed circuit boards, the backboard and the backpanel, The

backboard incorporates the sockets into which the various cards are

plugged whereas the backmost printed circuit board, the backpanel,

carries the outgoing plug/socket connections. These two boards are

electrically connected by two plugs in printed circuit boards, called

interconnectors. Connected to the backboard by a small wiring loom is

the power supply transformer (sometimes mounted externally in case of

static excitation systems) and the fixed front panel. The latter unit

houses the sensing and power supply fuses together with the remotely

controllable motorized voltage setting potentiometer and monitor reset

pushbutton, where applicable.

Each plug in card has unique polarizing key positions to prevent

cards being plugged into the incorrect position. The various cards

available, and their position in the mainframe (see fig.2-1) are listed

below separating the basic MAVR, its options and the static excitation

MAVR (see 2.3, 2.4 )


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O

O

A

Fixed Plate

B C D E F G H

O

O

[ Withdrawable Cards ]

Fig. 2-1 - MAVR Card Positions

2.2 The Basic Brushless System

This system comprises the mainframe together with the following

printed circuit cards:

2.2.1 Auto Power Card-fitted in position H

This is an assembly comprising a single phase half-controlled

thyristor bridge, its heatsink, a surge suppressor, and a semiconductor

protection fuse. This unit accepts the thyristor firing pulses which are

produced by the control card thereby controlling the excitation from

the permanent magnet generator excitation source.

2.2.2 Control Card-fitted in position E

This unit senses the voltage of R to Y and the current of B phase,

and produces thyristor firing pulses to control excitation. Also included

are an over flux circuit to reduced the excitation at reduced speed, a fast

acting field current limiter to prevent sustained high exciter field

current, a "soft start" facility to minimize voltage overshoot on build up,

and a diode failure detector to indicate failure of the rotating diode

assembly. The unit accepts control signals from the excitation limiter

and power factor control cards.


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2.2.3 Excitation Limiter Card-fitted in position D

This unit comprises over and under excitation transducers which

work in conjunction with the control card to prevent the excitation

being controlled above or below preset limits.

The limiter prevents prolonged overexcitation by controlling the

exciter field current, and has an integrating time delay to allow for high

transient field currents. If required, the operating level of the

overexcitation limiter can be temperature compensated to allow for

variation in generator cooling air temperature. The limiter also

prevents underexcitation and high internal load angles due to certain

leading power factor conditions and is quick acting to minimize

transients which could cause pole slipping.

2.3 Optional Extras

A power factor control card is available for use on the Standard

MAVR system, which includes auxiliary rack with electric hand control

board.

Where Twin AVR system is provided by a standby AVR Voltage and

excitation monitors are available, which may be plugged into the standard

MAVR rack.

2.3.1 Power Factor Control Card-fitted in position C

This unit in conjunction with the control card enables a parallel

running generator to be run at a constant power factor or reactive

current by driving the motorized voltage setting potentiometer also

incorporated in the MAVR.

Operation of the unit is initiated by an external signal ( normally

and auxiliary contact on the circuit breaker). An external signal will

also initiate automatic reduction of reactive current - a feature which is

useful when preparing to disconnect a generator from a power system.

A relay mounted in the mainframe may if required be used to inhibit


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the operation of the controller following manual operation of the

voltage setting control by the external volts raise/lower switch.

2.3.2 Excitation Monitor Card-fitted in position F

This unit comprises over and under excitation transducers which

operate a common monitor relay in the mainframe if the excitation is

controlled to a level outside a preset region.The latched monitor relay

can be used to initiate transfer to an alternative excitation system, and

local latched LED indication of over or under excitation monitor

operation is provided on the card front plate.

When the monitor is fitted to a MAVR a monitor reset pushbutton

would be mounted on the mainframe.

2.3.3 Voltage Monitor Card-fitted in position B

This unit comprises over and under voltage monitors each with an

integrating time delay. When either monitor operates the latched

monitor relay in the mainframe is energized and local latched LED

indication is provided on the card, relay and indication being resetable

by a pushbutton mounted on the mainframe.

The undervoltage monitor includes a circuit which prevents

operation hen the excitation is switched off, or when the generator

current exceeds a level corresponding to a fault at the generator

terminals.

The voltage monitor card would normally be fitted to initiate

transfer of excitation to a standby excitation system.

2.4 Static Excitation Systems

When the MAVR is used as the control element of a static excitation

system the auto power cards are omitted, and a special control card is

fitted in position E, which supplies a d.c. signal to the control circuits of

the thyristor converter, which will usually be situated in a separate

cubicle. Apart from the auto power cards the rest of the basic brushless


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system is used although various modification are made to the

mainframe such as the removal of the internal power supply. The

options available, as listed in 2.3, are also suitable for use in the static

system.

Due to the high excitation currents associated with static excitation

systems an additional sensing signal is required from the field current

via a D.C. current transformer. The power supply transformer is

mounted externally due to the increased size at the reduced operating

frequency of 50 or 60 Hz.


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3 MAINFRAME

3.1 SPECIFICATION

The mainframe houses the various cards and forms the necessary

interconnections. In addition it carries the ' Remote Volts Setting

Potentiometer ' , sensing fuses, transformers, and output relays.

The overall dimensions of the mainframe are: 177 mm high, 496 mm

wide and 409.5 mm deep. The typical weight of the complete unit is

approximately 14 Kg. It requires access at the back for the four 15-way

plug/socket connectors and adequate clearance above and below for

ventilation; 150 mm is recommended. The unit dissipates up to 200

watts when in operation.

3.1.1 Inputs

1) Voltage sensing supply:

110 V nominal, 50/60 Hz, red to yellow phase at 3 VA, &for the 3

phase

sensing option: yellow to blue phase at 3 VA.

2) Current sensing supply:

5A current transformer input, 50/60 Hz, blue line, burden 5 VA

maximum (with options).

3) Auxiliary supply:

220 V pilot exciter output at 400 Hz, 180 VA for a 50 Hz generator.

264 V pilot exciter output at 480 Hz, 180 VA for a 60 HZ generator.



220 V supply output at 50 Hz, 180 VA for a 50 HZ generator.

4) Excitation source:

220/264 V 400/480 Hz; 150/180 V 200/240 Hz, (400v on H.I.R.

unit ) pilot exciter output, capability dependent upon excitation

requirements but not exceeding 15 A, 220 V 50 Hz , capability


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dependent upon excitation requirements but not exceeding 15 A

continuous.

5) Auxiliary D.C. supply:

Selectable by internal links (on the backpanel ) for:

24 v + 25% ～ -20%

48 v + 25% ～ -20%

125v + 25% ～ -20%

220v +10% ～ -10%

Current rating 150 mA at all voltage taps.

3.1.2 Relay Outputs

Three relay outputs are available; one for the limiter card, one for the

various monitors, and one for the Diode Failure circuit.

1) Contact arrangement:

Normally open or normally closed all relay.

2) Contact rating:

220 V a.c./d.c., 100watts, 5 A, non-inductive.

3.1.3 Auxiliary Control Inputs

1) An external single pole changeover switch with centre 'OFF'

position is required to drive the internal motorized voltage setting

potentiometer.

Rating 150 V D.C. at 150 mA.

2) 'Field Application Contactor Auxiliary' for 'soft start' and 'under

voltage monitor override' ( single pole, normally open ). Rating 30V

D.C. at 10 mA.

3) Grid breaker auxiliary (single pole, normally open ) for use with

'Power Factor Control Card' . Rating 30 v d.c. at 10 mA.

4) VAr shed signal (signal pole, normally open ) for use with ' Power

Factor Control Card ', if required. Rating 30 v d.c. at 10 mA.

5) Smooth Changeover ' Signal ' ( single pole, normally open ) for use

with twin AVR schemes to reduce changeover shock with '


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Excitation Bias ' and ' Over Excitation ' units.

Rating 30 v d. c. at 60 mA.

6) A normally open contractor to give self-centering of MVSR Rating

150V d.c. at 150 mA.

3.1.4 Optional Input/Outputs

(1) Remote 'Level' potentiometer for' Excitation Bias/P.F. Control

Card '.

(2) External temperature compensation for over excitation limiter.

(3) Latching path for P.F. Control over-ride.

(4) Internal MVSR for twin AVR schemes.

(5) Smooth changeover single outputs/inputs for twin AVR schemes.

(6) Main amplifier input and output signals.

3.1.5 Ambient Temperature Range

Operating : -25 ℃ to + 65 ℃

Storage : -40 ℃ to + 100℃

3.1.6 External Connections

External connections are made by up to four 15 way plug/sockets, the

loose Plugs being wired to 3 metres of individually numbered 15 core

multicore cables, cross sectional area 1.0 mm2.

3.1.7 Extender Card

An extender card will be supplied mounted in the mainframe to give

access to test points on the various cards.

3.2 DESCRIPTION OF OPERATION

3.2.1 Introduction

The mainframe is the basic rack with all the plug in cards

withdrawn. The unit comprises the 19" rack assemble fitted with two

printed circuit boards, called the backpanel and backboard; fixed front

panel; and a power supply transformer which is fixed to the left hand

side plate of the rack.


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Interconnection between the backpanel and the backboard is made by

two printed circuit boards called interconnectors; and the backboard is

connected to the fixed front panel and power supply transformer by a

small wiring loom and a plug/socket to enable the fixed front panel to

be removed.

To select the various options available links are fitted on the

backpanel-these being set according to the specified contract

requirements.

3.2.2 Backpanel

The backpanel receives the plug/socket external connections and

carries the sensing transformers and auxiliary components as detailed

below.

Circuit

Reference Function

T1 Voltage sensing transformer energized via sensing

Fuses FS3 and 4 mounted on fixed front panel.

T2

Optional voltage sensing transformer used for three

phase sensing facility (not fitted on standard unit,

fitted on H.I.R. Unit)

T3,Z1,Z2,LK1

Sensing C.T. for excitation bias (EB) or power factor

control (PFC) card. Z1,Z2 provide C.T. load when

card withdrawn. CT is shorted by LK1 when EB or

PFC cards not fitted.

T4,Z3,Z4,LK2

Sensing C.T. for excitation monitor (EM) card.

Z3,Z4 provide C.T. load when EM card withdrawn.

C.T. is shorted by LK2 when EM card omitted.

T5,Z5,Z6 Sensing C.T. for excitation limiter (EL) card. Z5,Z6

provide C.T. load when card withdrawn.


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T6,Z7,Z8,LK3,

4,5,6

Sensing C.T. for control (c) card. LK3,4 will

normally be fitted and LK5,6 omitted to provide

quadrature current compensation (QCC) For

external reactance compensation LK3,4 will be

omitted and LK5,6 fitted. Z7,Z8 provide C.T. load

when C card is withdrawn.

R1,R2,LK8

AVR stabilizing resistors. R1,R2,LK8 fitted on single

AVR system; R1,LK8 only fitted on twin AVR system

when R1 on main and standby units are paralleled.

R3 Load resistor across output of Field rectifier to assist

thyristor turn on.

D1,D2,D3,D4

Flywheel diodes across output of Field rectifier, for

connector protection if power cards inadvertently

withdrawn during AVR operation.

RL1,R12,D5 Limiter operating relay, series dropper and Flywheel

diode.

RL2,R13,D6 Monitor operated relay, series dropper and flywheel

diode.

RL3,Z11,D7

Power supply monitoring relay. Energizes and causes

AVR transfer on a twin system if main AVR supply

fails. Energizes and causes AVR transfer to hand

control in the single AVR system if AVR supply fails.

RL4,D10,11,

12,R14,

R18

P.F. control inhibit latching relay. Relay is energized

through D11 or D12, and latched by RL4-1 and

external circuitry to inhibit p.f. control. Only used

when p.f. control card fitted.

R4,5,6,7,9,10

LK9,10,11,12,

13,14

Dropper resistors and voltage selection links for

internal motorized potentiometer.

Fit links LK9 & 10 for 24/30v dc supply.

LK11 & 12 for 50v dc supply.




15�

Z9,Z10 Stabilizing zeners for motorized potentiometer.

LK19,20,21 LK20,21 fitted only when P.F. control card is

supplied. LK19 is not fitted.

LK22,23

Both links are normally omitted. When fitted the

AVR amplifier input and pulse circuit input become

available at outgoing socket 4, pins 6 and 5

respectively.

R15,R16,D15,

D14,

C1,Z12

To effect a trip to hand control excitation on loss of

power supply with back-up excitation systems.

RL5,R17,D13,

LK26,

LK27

Diode Failure operated relay, series dropper and

flywheel diode, LK26 gives N/O contacts and LK27

N/C contacts.

LK28A,LK28B

Enables the Power Factor Control card option to be

used on 24/30v and 50v D.C. supplies. Fit neither

LK28A or LK28B for 120v D.C. Fit LK28A for 50v

D.C. Fit LK28B for 24/30v D.C.

INTERCHANGEABILITY

NOTE: LK24 and LK25 to be fitted only when replacing an original

version backpanel (G.A. B9602928 - PCB9602927). The 'Type A'

backpanel then becomes interchangeable, requiring no external wiring

changes.

3.2.3 Backboard (refer to fig. 3-3)

The backboard performs the function of interconnecting the various

printed circuit boards, transformer and fixed front panel. It provides

the stabilized D.C. supply for the cards and has various other auxiliary

components as detailed below.


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Circuit

Preference

Function

D1,2,3,4,C1,2 Power supply diodes and smoothing capacitors

Z1,2,C3,4

AVR power supply stabilizing zeners and smoothing

for control card electronics.

Z3,4,C5,6,R8,9

Auxiliary power supply stabilizing zeners and

smoothing for electronics not included on the

control card.

RL1,D5,6,VT1,

2,Z5,R3,4,5,6,7,

C7

Time delay circuit to inhibit transient operation of

Limiter, DFI and monitor relays immediately after

supplies connected to AVR RL1 will energize after a

delay provided the D.C. exceeds a pre-set level.

D7,Z6,R10 Provide feed to inhibit under-voltage monitor when

line current exceeds preset level.

LK1 Link which is removed when reset monitors

pushbutton fitted. This will usually be made on the

fixed front panel plug

3.2.4 Power supply Transformer (T1)

This unit isolates the electronics from the a.c. supply and provides

the correct voltage for the D.C. supply stabilizing circuit incorporated

on the backboard. It is also used to provide the phase reference and

frequency sensing signals for the control card.

An external transformer is used on some static excitation systems.

The primary tap used depends on the generator frequency and pilot

exciter viz:

R/B wire to TM2 for 200/240 Hz. 190v Newton PMG.

R/B wire to TM3 for 3,000 r.p.m. 220v Brush PMX exciter.

R/B wire to TM4 for 3,600 r.p.m. 264v Brush PMX exciter.

3.2.5 Fixed Front Panel (refer to fig 3-4)

This unit incorporates the volts setting potentiometer, monitor


17�

reset-pushbutton and supply/sensing fuses as detailed below.

Circuit

Reference Function

FS1,FS2

Auxiliary a.c. fuses in primary of transformer T1 or

in a.c. supply to power supply bridge on static

excitation systems

FS3,FS4,(FS5)

Voltage sensing fuses in primary of back panel

mounted sensing transformer T1 (FS5 is not

normally fitted but will be fitted when AVR

incorporates 3 phase sensing and T2 is fitted to back

panel).

RV1,RV2

Voltage setting potentiometer. On a twin AVR

system, the standby unit incorporates the voltage

setting control for both unit units. RV2 sets the

voltage of the main AVR.

(RV2 may not be fitted in a single AVR system).

M,LS1,LS3

Motor assemble for driving voltage setting control

incorporates limit switches LS1 and LS3. M, RV1,

RV2 will not be fitted on the main AVR of a twin

MAVR system.

LS2 & LS4 Limit switches for driving the voltage setting control

to the centre of its range (i.e. selfcentering).

PB1 Reset monitors pushbutton fitted to AVR's

incorporating latched Fault monitors.

The components fitted on a particular unit will vary according to

contract requirements, typically FS1,2,3 & 4, RV1,M,LS!,2,3 & 4 are

fitted on a standard unit.PB1 is normally fitted in place of M, RV1 and

2, LS1,2,3 & 4 in the case of the main unit of a twin system whereas the

standby unit is usually a standard unit.


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3.3 COMMISSIONING PROCEDURE

This section describes the commissioning procedure for the

mainframe and should be read in conjunction with the general

commissioning procedure, section 11 and any specific contract

commissioning instructions

IMPORTANT:

(1) Check that the correct links are fitted on the backpanel as

detailed in the test records for MAVR tested with a test

generator. (sub-section 6)

(2) Check that the correct power supply transformer tap has been

selected.

In general the majority of the commissioning procedure of a MAVR

unit is covered by the procedure for the individual cards, see the

appropriate instructions. However prior to running the set the

following static checks should be carried out.

1) Check all connections associated with the mainframe are sound and

tight.

2) Check all external wiring to 0NQ.359.019 MAVR Excitation system

circuit diagram paying particular attention to the phasing of the P.T.

and C.T. feeds.

3) Apply the D.C. supply to the mainframe and check corrector

operation of the motorized voltage setting potentiometer, i.e.

clockwise rotation for a 'raise' signal and vice versa.

3.4 FAULT FINDING PROCEDURE

This section describe the fault finding procedure for the mainframe

and should be read in conjunction with the general fault finding section

12.


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IMPORTANT:

(1) The majority of excitation faults are caused by incorrect connections

- thoroughly check all connections are correct to the circuit diagram.

(2) Check the correct links are fitted as detailed in the test records for

MAVR tested with a test generator. (sub-section 6)

Before commencing fault finding on the mainframe exhaust all the

pertinent faults given in the general fault finding section 12 and the

detailed faults given in the individual card sections.

The following tables give the required signals on each finger of the card

sockets and the path from those fingers to the source or output. Card

fingers/sockets are referred to as bracketed numbers, output

connections as socket number/pin number and each card is abbreviated

thus:

Control C

Auto Power AP

Excitation Limiter EL

Excitation Monitor EM

Power Factor Control PFC

Volts Monitor VM

Interconnector I1-5 & I9-6

By tracing through the signals present on the socket of a suspected

faulty card the nature of the fault can be deduced and corrective action

taken.

Table 3-1 CONTROL CARD

SKT Title Required Signal Path Possible

Fault

1 If pick-up

O.165v/A

excitation w.r.t.

C(29) - brushless

only.

Via I9-6(3)

to R1/R2 &

1/14.

R1/R2

faulty.


20�

2 AVR Amp

i/p Zero w.r.t. C(29)

Via I1-5(3)

& LK23 to

4/6

Control card

faulty

3 QCC

C.T.M

1.53v/A sensing

current w.r.t.

C(6) Maximum

Q.C.C

Via I1-5(6)

& LK3 or

LK6 to T6

T6 or control

card faulty.

4 42v a. c.R.

42v a.c. @105v.

Sensing volts

w.r.t.C(6)

Via I1-5(8)

to T1

T1 of control

card faulty.

5 42v a.c.B.

42v a.c. @105v.

Sensing volts

w.r.t. C(4)-three

phase sensing

only.

Via I1-5(10)

to T2

T2 or control

card faulty.

6 42v a.c.Y. See(4) Via I1-5(12)

to T1

T1 or control

card faulty.

7 +ve AVR

P.S.

+15v D.C. w.r.t.

C(29)

To Z1

(Backboard)Z1 faulty.

8 Not used

9 Not used

10 SCR1

cathode

Negative pulse

w.r.t. C(13) To AP(12)

Auto power/

control card

faulty.

11 P.S. A.C 54v a.c. w.r.t.

C(29)

To T1

terminal(5) T1 faulty.

12 P.S. A.C 54v a.c. w.r.t.

C(29)

To T1

terminal(7) T1 faulty.

13 SCR1 gate Positive pulse

w.r.t. C(10) To AP(13)

Auto power/

Control card

faulty.

14 Not used.


21�

15 Pulse CCT

O/R

±0.7v D.C. w.r.t.

C(29)

Via I1-5(27)

& LK22 to

4/5

Control card

faulty.

16 Not used.

17 SCR2

cathode

Negative Pulse

w.r.t.

C(18)

To AP(14)

Auto power/

Control card

faulty.

18 SCR2 gate

Positive pulse

w.r.t.

C(17)

To AP(15)

Auto power/

Control card

faulty.

19 -ve Unreg. -76v D.C. w.r.t.

C(29)

To C2,D2,D4

(backboard)

T1 or C2,D2,

D4 faulty.

20 +ve Unreg. -76v D.C. w.r.t.

C(29)

To C1,D1,D3

(backboard)

T1 or C1,D1,

D3 faulty.

21 -ve AVR

P.S.

-15v D.C. w.r.t.

C(29) To Z2 Z2 faulty

22 AVR Amp

Com. Zero w.r.t. C(29)

Via I1-5(42)

to 4/10

Control card

faulty.

23 Internal

MVSR2

500 ohm w.r.t. to

C(29) at

minimum set

volts with

control card

removed.

To fixed

front panel

via BK/O

wire &

I1-5(43) to

4/11.

RV1 faulty.

24 Reset 1 +15v D.C. w.r.t.

C(29)

To PB1 or

T1 via O/BN

wire.

PB1 faulty

or O/BN not

shorted to

O/GN on T1.

25 U.V.

override Zero w.r.t. C(29) To VM(28)

Control card

or Z6,D7 on

backboard

faulty.


22�

26 FAC Aux. +15v D.C. w.r.t.

C(29)

Via I1-5(28)

to 2/11

Control card

faulty.

27 Not used.

28 D.F.I. Relay

+15v D.C. w.r.t.

C(29) when

D.F.I. operating

Via I1-5(50)

to RL5 &

R17.

D.F.I. faulty.

29 common Zero

Via

I9-6(51-60)

to R1/R2

Mainframe

faulty.

Table 3-2 AUTO POWER CARD

SKT

No. Title Required Signal Path

Possible

Fault

(1-5) Field +ve

Field voltage

(+ve) w.r.t.

AP(29)

Via I9-6(5 to

11) to 1/1 &

1/2.

Auto power

card faulty.

(6-1

0)

Common

A.C.

220/264v(150/180

v) a.c. (400v on

H.I.R.unit.) w.r.t.

Ap(20)

Via I9-6(13

to 19) to 1/3

& 1/4

External

fault.

(11) Not used.

(12) SCR1

Cathode

Negative pulse

w.r.t. AP(13) To C(10)

Auto Power/

Control card

faulty.

(13) SCR1 Gate Positive pulse

w.r.t. AP(12) To C(13)

Auto Power/

Control card

faulty.

(14) SCR2

Cathode

Negative pulse

w.r.t. AP(15) To C(17)

Auto Power/

Control card

faulty.

(15) SCR2 Gate Positive pulse

w.r.t. AP(14) To C(18)

Auto Power/

Control card


23�

faulty.

(16) Not used.

(17) Not used.

(18) Not used.

(19) Not used.

(20-

24) Auto A.C

220/264v(150/180

v) a.c.w.r.t. AP(6)

Via I9-6(42

to 49) to 1/7

& 1/8

External

fault

(25-

29)

Output -ve

(Common)

Negative voltage

w.r.t. AP(1)

Via I9-6 (51

to 69) to

R1/R2

Mainframe

faulty

Table 3-3 EXCITATION LIMITER CARD

SKT


Possible

Fault

(1) Reset 2 +15v D.C. w.r.t.

EL(29)

To RL-1

(Backboard

and PBI or

T1 via O/GN

wire

RL1 faulty.

(2)

If pick-up

0.165v/A

excitation w.r.t.

EL(29)-

brushless only.

Via I5-6(3)

to R1/R2 &

1/14

R1/R2

faulty.

(10) OEL Temp

comp 3 Not used.

Via I5-6(48)

to 3/13 Not used

(11) Not used.

(12) Limiter

O.R.

+15v D.C. w.r.t.

EL(29) when

Monitor O.R.

given to 3/7

Via I1-5(29)

to 3/7

Limiter/

Monitor or

external

signal faulty


24�

(13) SCO

Selector

+15v D.C. w.r.t.

EL(29) on twin

system when on

other AVR.

Not used on

single AVR

Via I1-5(29)

to 4/3

External

faulty

(14) -ve Aux.

P.S.

-15v w.r.t.

EL(29)

To Z4

(Backboard)Z4 faulty

(15) Pulse cct

O/R

+0.7v D.C. w.r.t.

EL(29)

To C(15) and

via I1-5(27)

& LK22 to

4/5

Control/

Excitation

Limiter

faulty.

(16) +ve Aux.

P.S.

+15v D.C. w.r.t.

EL(29)

To Z3

(backboard) Z3 faulty

(17) Limiter

Relay

+15v D.C. w.r.t.

EL(29) when

Limiter

operating

Via I1-5(25)

to R12/RL1 R12/RL1

(18) Ext. OEL

Amp

Not used on

single system ±

10v D.C. w.r.t

EL(29) on twin

system

Via I1-5(51)

to 3/12

Other AVR

faulty

(19) -ve Unreg. -76v D.C. w.r.t.

EL(29)

To C2,D2,D4

(Backboard)

T1 or C2,D2,

D4 faulty.

(20) +ve Unreg. +76v D.C. w.r.t.

EL(29)

To C1,D1,D3

(Backboard)

T1 or C1,D1,

D3 faulty.

(21) 2.5v A.C.

R-Y

2.5v D.C. w.r.t

EL(29)

Via I1-5(46)

to T1 T1 faulty.

(23) Int OEL

Amp.

±10v D.C. w.r.t.

EL(29)

Via I1-5(52)

to 3/10

Excitation

Limiter

faulty


25�

(24) OE. Temp

Comp. 2

-1v to -5v D.C.

w.r.t. EL(26)

when external

temp. Comp.

Unit fitted

Via I1-5(53)

to 4/12

Main Frame

faulty or

external

temp. Comp

unit faulty

(25)

Exc.

Lim/Mon

Link

As EL(26) To EM(25) Mainframe

fault

(26) OE Temp

Comp. 2

+1v to +5v D.C.

w.r.t. EL(24)

when external

temp. Comp.

Unit fitted

Via I1-5(54)

to 4/13

External

temp. Comp.

Unit fault or

main frame

fault.

(27) UEL C.T.L.

4.5v/A-sensing

current. W.r.t.

EL(28)

Via I1-5(55)

to T5 T5 faulty.

(28) UEL

C.T.M.

4.5v/A-sensing

current. W.r.t.

EL(27)

Via I1-5(56)

to T5 T5 faulty.

(29) Common Zero

Via

I9-6(51-60)

to R1/R2

Mainframe

faulty.

Table 3-4 POWER FACTOR CONTROL CARD

SKT

NO. Title Required Signal Path

Possible

Fault

(1) P.F. +ve P.F.C. +ve

auxiliary D.C.

Via I1-5(1)

to 3/9

External

wiring

(4) Ext. Pot. H

Remote PFC

level only. 5

kohms w.r.t.

PFC(6) with

card removed.

Via I1-5(4)

to 4/4

External

wiring fault.


26�

(5) Ext. Pot. A

Remote PFC

level only. 5

kohms w.r.t.

PFC(6) with

card removed

and dependant

on pot position

Via I1-5(5)

to 4/2

External

wiring fault.

(6) Ext. Pot. L

5 kohms w.r.t.

PF(4) when card

removed.

Via I1-5)(7)

to 4/1

External

wiring fault.

(7) PFC Raise PFC-Raise signal

to MVSR

Via I1-5(9)

to 3/3 and

via LK20 to

Z10 &

MVSR

Other AVR

fault

PFC faulty

(8) PFC Lower PFC-Lower

signal to MVSR

Via I1-5(11)

to 3/1 and

via LK21 to

Z9 & WVSR

PFC faulty

(9) Grid C/B

Aux.

+15v D.C. w.r.t.

PFC(29)

Via I1-5(13)

and

LK19/RL4-3

to 2/3.

External

fault

(10) VAr shed

+15v D.C. w.r.t.

PFC(29) when

VAr shed

selected.

Via I1-5(15)

to 2/3

External

fault

(11) PFC CTM

6.0v/A-sensing

current w.r.t.

PFC(12)

Via I1-5(18)

to T3 T3 faulty


27�

(12) PFC CTL

6.0v/A-sensing

current w.r.t.

PFC(11)

Via I1-5(16)

to T3 T3 faulty

(13) SCO

Selector

PFC-not used

EB-+15v D.C.

w.r.t. EB(29)

when other AVR

selected.

Via I1-5(19)

to 4/3

External

fault

(14) -ve Aux P.S. -15v D.C. w.r.t.

PFC(29)

To Z4


(16) +ve Aux

P.S.

+15v D.C. w.r.t.

PFC(29)

To Z3


(21) 2.5v

A.C.Y-R

2.5v a.c. w.r.t.

PFC(29)

Via I1-5(46)

to T1 T1 faulty


PFC(29)

To C2,D2,D4

(backboard)

T1 or

C2,D2,D4

faulty


PFC(29)

To C!,D1,D3

(backboard)

T1 or

C1,D1,D3

faulty

(29) Common Zero

Via

I9-6(51-60)

to R1/R2

Mainframe

Faulty

Table 3-5 EXCITATION MONITOR CARD

SKT


Possible

Fault

(2) If Pick-up

0.165v/A-excitati

on w.r.t. EM(29)-

brushless only.

Via I9-6(1)

to R1/R2 &

1/14

R1/R2 faulty


28�

(9) Monitor.

Relay

+15v D.C. w.r.t.

EM(29) when

monitor

operating

Via I1-5(14)

to R13 &

RL2

Monitor or

RL2 faulty

(14) -ve Aux.

P.S.

-15v D.C. w.r.t.

EM(29)

To Z4


(16) +ve Aux.

P.S.

+15v D.C. w.r.t.

EM(29)

To Z3


(18) Exc. Mon.

O.R.

+15v D.C. w.r.t.

EM(29) when

Monitor override

signal given to

3/7

Via I1-5(29)

to 3/7

Monitor or

external

signal faulty.

(19) UEM

C.T.L.

4.5v/A-sensing

current w.r.t.

EL(20)

Via I1-5(44)

to T4 T4 faulty

(20) UEM

C.T.M.

4.5v/A-sensing

current w.r.t.

EL(19)

Via I1-5(45)

to T4 T4 faulty

(21) 2.5v A.C.

R-Y

2.5v a.c. w.r.t.

EM(29)

Via I1-5(46)

to T1 T1 faulty


EM(29)

To C1,D1,D3

(Backboard)

T1 or

C1,D1,D3

faulty


EM(29)

To C2,D2,D4

(Backboard)

T1 or

C2,D2,D4

faulty

(24) Reset 1 +15v D.C. w.r.t.

EM(29)

To PB1 or

T1 via O/BN

wire

PB1 faulty

or O/BN not

shorted to

O/GN on T1.


29�

(25)

Exc.

Lim/Mon

Link

As EL(26) when

EL fitted To EL(25) Main frame

(29) Common Zero

Via

I9-6(51-60)

to R1/R2

Mainframe

faulty.

Table 3-6 VOLTAGE NONITOR CARD

SKT


Possible

Fault

(2) Volts Mon

O.R

+15v D.C. w.r.t.

VM(29) when

Monitor override

signal give to

3/11

Via I1-5(2)

to 3/11

Monitor or

external

signal fault

(8) Monitor

relay

+15v D.C. w.r.t.

VM(29) when

monitor

operating

Via I1-5(14)

to R13 and

R12

Monitor or

RL2 faulty

(12) -ve Aux.

P.S.

-15v D.C. w.r.t.

VM(29)

To Z4


(13) +ve Aux.

P.S.

+15v D.C. w.r.t.

VM(29)

To Z3


(20) Sensing

R105v

105v a.c. w.r.t.

VM(22)

Via FS4 Y

I1-5(39) to

T1

FS4 or main

frame faulty

(22) Sensing

Y105v

105v a.c. w.r.t.

VM(20)

Via FS3 Y

I1-5(34) to

2/9

FS3 or main

frame faulty

(24) Reset 1 +15v D.C. w.r.t.

VM(29)

To PB1 or

T1 via O/BN

PB1 faulty

or O/BN not

shorted to


30�

O/GN on T1.


VM(29)

To C2,D2,D4

(Backboard)

T1 or

C1,D2,D4

faulty

(26) +ve Unreg. -+8v D.C. w.r.t.

VM(29)

To C1,D1,D3

(Backboard)

T1 or

C1,D1,D4

faulty

(28) U.V.

Override

Zero w.r.t.

VM(29) To C25

Volts

monitor/

Control card

faulty or

Z6,D7 on

Backboard

faulty.

(29) Common Zero

Via

I9-6(51-60)

to R1/R2

Main frame

fault.

Table 3-7 OUTGOING SOCKET NO.1

SKT

No.

Title Required Signal Path Possible

Fault

1/1

&

1/2

Field +ve Field Voltage

w.r.t. 1/10

Via

I9-6(5-11) to

AP(1-5)

Mainframe

faulty

1/3

&

1/4

Common

A.C.

220/264v(150/180

v) a.c. w.r.t. 1/7

and 1/8

Via

I9-6(13-19)

to AP(6-10)

Mainframe

faulty

1/7

&

1/8

Auto A.C.

220/264v(150/180

v) a.c. w.r.t. 1/3

& 1/4

Via

I9-6(43-49)

to AP(20-24)

Mainframe/e

xternal

wiring faulty


31�

1/9 MVSR

Raise +ve

Auxiliary D.C.

+ve when raise

signal given

Via D8, Z10,

I-5(36) to

MVSR

Faulty

MVSR, D8

or Z10

1/10

Field

-ve/Commo

n -ve

-ve Field voltage

w.r.t. 1/1 or 1/2 To LK8

Mainframe/

Link

omission

fault

1/11 Aux. A.C. 220/264v(150v/1-

80v) a.c. w.r.t. 3/6

Via I1-5(20)

to FS2

External

wiring fault

1/12 MVSR

Lower +ve

Auxiliary D.C.

+ve when lower

signal given

Via D9, Z9,

I1-5(35) to

MVSR.

Faulty

MVSR, D9

or Z9.

1/13 Blue C.T.M. Passes sensing

current

To 1/15 via

T3, T4 or

LK2, T5 &

T6

External

wiring

fault/LK2

omitted if T4

not fitted

1/14 Field -ve -ve field voltage

w.r.t. 1/1 or 1/2 To R1/R2

Mainframe

failure

1/15 Blue C.T.L. Passes sensing

current

To 1/13 via

T3, T4 or

LK2, T5 &

T6

External

wiring

fault/LK2

omitted if T4

not fitted.

Table 3-8 OUTGING SOCKET NO.2

SKT

NO.

Title Required Signal Path Possible

Fault

2/1 Grid

Breaker

Aux.

+15v D.C. w.r.t.

1/14 when PFC

operation

selected

Via

LK19/RL4-3

& I1-5(13) to

PFC(9)

LK19/RL4-3

faulty

2/2 Monitor RL Short circuit to To RL2-1 RL2 faulty


32�

n/c 2/4 when no

monitor

operating

2/3 VAr shed

selector

+15v D.C. w.r.t.

1/14 when 'VAr

shed' selected

Via I1-5(15)

to PFC(10)

External

fault.

2/4 Monitor RL

com

See 2/2 & 2/6 To RL2-1 RL2 faulty

2/6 Monitor RL

n/o

Short circuit to

2/4when a

monitor is

operating

To RL2-1 RL2 faulty

2/7 Incoming

Y105v

105v a.c. w.r.t.

2/9

Via I1-5(32)

to FS4

External

fault

2/8 Limiter RL

n/o

Shirt circuit to

2/10 when the

Limiter is

operating

To RL1-1 RL1 faulty

2/9 Incoming

Y105v

105v a.c. w.r.t.

2/7

Via I1-5(34)

to FS3

External

fault

2/10 Limiter RL

com.

See 2/8 & 2/12 To RL1-1 RL1 faulty

2/11 FAC Aux. +15v D.C. w.r.t.

1/14 when FAC

closed

Via I1-5(28)

to C26

External

fault

2/12 Limiter RL

n/c

Short circuit to

2/10 when the

limiter is not

operating

To RL1-1 RL1 faulty

2/13 Astatic

C.T.L

1V/A sensing

current w.r.t.

2/15 - Maximum

Q.C.C.

To T6 T6 faulty


33�

2/13 Astatic

C.T.L

1V/A sensing

current w.r.t.

2/15 - Maximum

Q.C.C.

To T6 T6 faulty

2/14 MVSR

Supply-ve

Auxuiliary D.C.

-ve

To LK9 to 14

and RL4

External

fault

2/15 Astatic

C.T.M.

See 2/13 To T6 T6 faulty


SKT

No. Title Require Signal Path

Possible

Fault

3/1 PFC Lower

±7.5v D.C. w.r.t.

4/10 -PFC-Lower

signal to MVSR

Via I1-5(11)

to PFC(8) &

Via LK21 to

Z9 & MVSR

PFC Faulty

3/2 P.F. Control

Latch

Auxiliary D.C.

+ve unless

resetting

To RL4 via

RL4-1

External

fault

3/3 PFC Raise

±7.5v D.C. w.r.t.

4/10 -(twin

system only)

PFC-Raise signal

to MVSR

Via I1-5(9)

to

EB/PFC(7)

& via LK20

to Z10 &

MVSR

EB-Other

AVR fault

PFC-PFC

faulty

3/4

Standby

select RL

com twin

system or

hand

control sel

RL com

single

system

+15v D.C. w.r.t.

4/10

To D7,Z11 &

RL3

Other AVR

faulty Hand

control

faulty


34�

3/5 Trip Supply

To PMG 50%

Tap or Hand

Control supply

To D14 (&

LK25) &

associated

components

External

fault

3/6 Aux. A.C.

Com. See 1/11

Via I1-5(24)

to FS1

External

wiring fault

3/7 Ecx. Mon

O.R.

+15v D.C. w.r.t.

4/10 when

monitor override

signal given to

3/7

Via I1-5(29)

to EM(18)

EM or

external

fault

3/8 MVSR

Centre

Aux. D.C. +ve

when

self-centering

required

Via I1-5(60)

to MVSR

Faulty

MVSR or

external

signal

3/9 PF +ve +ve auxiliary dc

Via I1-5(1)

to

EB/PFC(1)

External

fault

3/10 Int. OEL

Amp.

±10v D.C. w.r.t.

4/10

Via I1-5(52)

to EL(23)

Excitation

Limiter

faulty

3/11 Volts Mon

O.R.

+15v D.C. w.r.t.

4/10 when

monitor override

Signal give to

3/11

Via I1-5(20)

to VM(2)

Monitor or

external

fault

3/12 Ext. OEL.

Amp

Not used on

single system ±

10v D.C. w.r.t. to

4/10 -on twin

system

Via I1-5(51)

to EL(18)

Other AVR

fault


35�

3/13 OEL Temp

Comp 3.

Zero voltage

w.r.t. 1/14 if E.L

fitted

Via I1-5(48)

to EL(10)

Mainframe

faulty or EL

faulty

3/14

3/15

DFI Relay

DFI Relay

N/C if link LK27 fitted to RL5

via LK26

N/O if link LK26 fitted to LK27

Link missing

or RL5

faulty


SKT

No. Title Require Signal Path Possible Fault

4/1 Remote PFC

pot. L

5 kohms w.r.t. 4/4

with PFC card

removed

Via I1-5(7) to

PFC(6)

External

faulty

4/2 Remote PFC

pot. A

0-5 kohms w.r.t. 4/4

with PFC card

removed

Via I1-5(5) to

PFC(5) External fault

4/3 Common

SCO selector

+15v D.C. w.r.t.

1/14 when other

AVR selected twin

system only

Via I1-5(19)

to PFC(13) &

EL(13)

External fault

4/4 Remote PFC

pot.H. See 4/1

Via I1-5(4) to

PFC(4) External fault

4/5 Pulse cct.

O/R

± 0.7v D.C. w.r.t.

1/14

Via LK22 &

L1-5(27) to

C15

Control card

fault. LK22

not normally

fitted

4/6 AVR amp. i/p Zero w.r.t. 1/14 Via LK23 &

I1-5(3) to C2

Control card

fault. LK23

not normally

fitted


36�

4/7 External

MVSR2

500 ohms w.r.t. 4/8

at minimum volts

set & external

wiring removed

Via I1-5(30)

to MVSR

Mainframe

fault

4/8 External

MVSR1

500 ohms w.r.t. 4/7

at minimum volts

set & external

wiring removed

Via I1-5(31)

to MVSR

Mainframe

fault

4/9 Incoming

B105v

105v a.c. w.r.t. 2/9

& 2/8 when 3-c

sensing fitted.

Via I1-5(33)

to FS5 External fault

4/10 AVR Amp.

Com. Zero w.r.t. 1/14

Via I1-5(42)

to C(22)

Mainframe

fault.

4/11 Internal

MVSR2

500 ohms w.r.t. 4/10

at minimum volts

set & control card

removed

Via I1-5(43)

to C(23)

Mainframe

fault.

4/12 OEL temp.

Comp.2

Zero volts w.r.t.

1/14 if E.L. fitted.

Via I1-5(53)

to EL(24)

Main frame or

E.L. frame

fault

4/13 OEL Temp.

Comp.1

1v to 5v D.C. w.r.t.

1/14 when temp

comp. connected

externally.

Via I1-5(54)

to EL(26) External fault


37�


38�


39�


40�

4. CONTROL CARD

4.1 SPECIFICATION

4.1.1 Steady State Voltage Regulation

The generator voltage is maintained within ±1% of the selected

operation voltage subject to the following conditions:

1) The ambient temperature must not deviate by more than ±15℃

from that temperature at which nominal voltage is first set.

2) The frequency deviation must not exceed ±10% of the nominal

frequency (50 or 60Hz).

3) The sensing voltage supplied to the unit must be a constant

proportion of the generator output.

4) The current limit circuit is not operating.

The generator voltage will be maintained within ±0.5% of the

selected operating voltage when the generator load is switched from

no-load to full-load provided there is zero quadrature current

compensation.

4.1.2 Nominal Detector Supply Voltage

Within the range 100~120 volts.

4.1.3 Operating Voltage Range

An adjustment of ±10% on nominal voltage is provided by the

voltage setting rheostat which is controlled either manually or remotely.

A larger voltage setting range is available but is non-standard.

4.1.4 Parallel Operation

An internal current transformer is provided, an isolated primary

winding of which is supplied from the 5 amp. Secondary winding of an

instrument current transformer in the generator output. The internal

current transformer and its load represents a burden of less than 1 VA.

Two modes of parallel operation of the generator are normally available;

the quadrature current compensation and astatic compensation, and


41�

the degree of stability of reactive current is determined by the setting of

a rheostat in the AVR.

To convert to astatic compensation, a third winding is provided on

the AVR internal current transformer and these should be connected in

a operated in parallel.

In the quadrature current compensation mode 15% droop at full

load zero power factor is available. For compensation of external

reactance the droop can be inverted by internal links to give up to

15% external reactance compensation.

If the nominal CT current is less than 5 amps, the amount of

compensation will be reduced in proportion.

4.1.5 Frequency Fall Off

1) The fall off frequency is set to:

42.5 Hz on a 50 Hz system ) selected by

51 Hz on a 60 Hz system ) internal links

2) The fall off frequency does not vary by more than 2% of the setting

provided the temperature variation is less than ±15℃ from

ambient and the pilot exciter output voltage is within ±25% of

nominal voltage tap selected on power transformer.

3) The generator output will be linearly reduced to between 50% and

30% of nominal at 50% of the falling frequency set point.

4) Below 50% speed the characteristic is less predictable but over

fluxing will be prevented.

4.1.6 Diode Failure Indicator

1) This unit detects field current ripple and gives an output signal to a

relay mounted in the mainframe and also gives local indication

when the ripple exceeds a preset proportion of the field current.

2) Normal Sensitivity (with link 12 and 13 omitted). The relay will

operate when the negative peak of ripple in exciter field current

exceeds 20% of the d. c. level.


42�

3) Increased sensitivity (link 12 fitted and 13 omitted). The ripple to operate

the relay is adjustable using RV6 from 20% to 12% of the d. c. level.

4) Reduced sensitivity (link 12 omitted and 13 fitted). The ripple to operate the

relay is adjustable using RV6 from 20% to 40% of the d. c. level.

4.1.7 Current Limiter

1) This circuit is incorporated to limit the maximum continuous field

current, and has a quick acting inverse timer delay characteristic

for short circuit current limiting.

2) The field current limit can be set within the range 5 to 25 A; the

time delay is fixed at 20% second ±10%.

3) A link can be changed to increase the sensitivity by a factor of 10 (±

0.5) as a commissioning aid.

4.1.8 Soft Start Circuit

This circuit uses an external ‘Field Application Contractor’

auxiliary contact to detect excitation build up and utilizes this to slowly

ramp up the voltage reference to minimize over shoot on build up.

4.1.9 Ambient Temperature Range

Operating: -25℃ to 65℃

Storage : -40℃ to 100℃

4.1.10 Power Supply Requirements

The card draws its ±15volt power supplies from the mainframe.

The power supplies are adequate from 120% to50% of nominal

frequency and nominal pilot exciter voltage range of 120% to 40%.

4.1.11 Input Signals

The unit requires a single phase, 100 to 120 volts, B to A phase

supply of 2 VA rating. It also requires a 5A current transformer input of

1VA rating in the C phase.

4.1.12 Remote Voltage Setting Potentiometer

Fine adjustment (±10%) on the nominal voltage is provided by a


43�

500 ohms 1W potentiometer that is either mounted in the mainframe or

mounted externally.

4.1.13 Controls and Indications

1) Set V: A front access multi-turn potentiometer to set the nominal

voltage.

2) Q.C.C. A front mounted single turn potentiometer with a calibrated

dial scaled 0 ~ 10 which sets the level of quadrature current

compensation.

3) Set Q: A front access multi-turn potentiometer that adjusts the

stabilizing signal magnitude.

4) Set P: A front access multi-turn potentiometer that adjusts the

stabilizing signal phase.

5) Test DF: A front mounted pushbutton to test the ‘Diode Failure

Indicator’ circuit operation.

6) D.F.I.: A front mounted ‘Light Emitting Diode’ to give indication

of rotating diode failure.

7) Set DF: A front access multi-turn potentiometer to set the sensitivity

of the ‘Diode Failure Indicator’.

8) If LIM: A front access multi-turn potentiometer to set the maximum

continuous field current controlled by the ‘Current Limit’.

9) Step: A pushbutton mounted on the printed circuit board that can

be used to provide a 10% step to AVR reference.

Can be used when setting up response during commissioning.


(Numbers in brackets ( ) refer to printed circuit board edge

connections, and all voltage levels are relative to TP1.)

The unit is supplied with –15V(21), 0V(29), +15V(7) stabilized rails

derived from Z1, Z2, C3, C4, on the backboard. When the control

card is inserted in the rack, R1, R2, R5, R6 supply current to the power


44�

supply zeners on the backboard.

4.2.1 The Detector and Amplifier

Sensing voltage is supplied to DB1 at (3) (4) (6) from T1 and T6

mounted on the back panel. RV1 adjusts the voltage across (3) and (6)

and the amount of quadrature current (or external reactance)

compensation, i.e. drooping (or rising) voltage with increasing lagging

vars.

The sensing voltage is attenuated, smoothed and compared with a

reference signal produced by Z1 and R14, and the resultant error

supplied to the AVR amplifier, IC1, which is gain stabilized by R16.

RV2 provides coarse voltage adjustment and RV1 on the fixed front

panel connected across (22) and (23), the fine adjustment.

4.2.2 Auxiliary Control Signals

Auxiliary control signals can also be supplied to the input to the

voltage error amplifier via (2). If this facility is utilized the signal,

which should be isolated, should be supplied to the multi-core 4/10 and

4/6, and link LK23 on the back panel fitted.

4.2.3 Pulse Circuit

VT1, 2, 3, PUT1, T1 and associated components form the pulse

circuit.

At the beginning of each half cycle of the permanent magnet

generator (PMG) output waveform, the voltage TP3 to TP1 is

approximately 0.5 volts negative due to D6 and D7 being forward

biased by R22. When the PMG voltage increases from zero, D8 is

forward biased by R21 and D9 or D10 and D6 is charged from –0.5

volts towards the amplifier output voltage at TP2, through resistor R17.

After a delay dependant on the voltage at TP2, VT1 will be turned on,

VT2 turned off, causing the voltage at the anode of PUT1 to rise. When

the voltage at the anode of programmable injunction transistor PUT1

reaches a level set by the ratio of R25 and R29, the PUT switches on,


45�

and the voltage across R28 rises rapidly to a level set by R24 and R28.

Transistor VT3 is turned on for a short period by a pulse or current

through R27 and C8 and C9 rapid discharges through the primary

winding of pulse transformer T1 and VT3. A pulse is produced across

each secondary winding of T1 that is connected to SCR1 gate via (13)

and (10) and SCR2 gate via (17) and (18).

At the end of the half cycle of PMG output waveform, D8 becomes

reverse biased and D6 and D7 forward biased by R22, the voltage at

TP3 falling to –0.5 volts. VT1 turns off, VT2 on, and the voltage at the

anode of the PUT falls to a low level, in preparation for the next pulse,

which occurs during the next half cycle. When VT3 ceases conduction,

C9 is charged to approximately +15 volts via R26.

The time taken to charge C6 is dependent on the amplifier output

voltage, which varies according to the firing angle of the thyristors.

Figure 4-1 shows the capacitor and output voltage waveforms for high

and low amplifier output voltage.

An additional feed to C6 via (15) makes it possible for the

excitation limiters to over-ride the amplifier output signal there by

preventing over or under excitation beyond preset limits.

In addition, when LK6 is inserted in the control card, the earliest

possible firing angle can be limited by the output of IC2b, the field

current limit amplifier.

4.2.4 AVR Stabilizing

On a brushless generator the voltage control loop is stabilized by

transient feedback from exciter field current.

The voltage from the stabilizing resistor (R1, R2 on back panel) is

supplied to the input of IC1 via (1), LK1, C1, C2, RV3 and R12. RV4

adjusts the amplitude of the stabilizing signal, and RV3, the phase. LK2

is not fitted:


46�

4.2.5 Field Current Limit

When the current in the exciter field exceeds a level depending on

the setting of RV5, the voltage at the output of IC2b begins of fall.

D17 begins to conduct, and current flows through LK6 and R53,

thereby reducing the rate at which C6 is charged and delaying the

firing angle. The output voltage of IC2b settles at a value whereby the

voltage at the wiper of RV5 is controlled to the voltage at pin 6 of IC2b,

which corresponds to a preset field current.

4.2.6 Falling Frequency (Over Flux) Protection

The output of the supply transformer is fed via R33 and (11) to a

frequency sensitive circuit. On alternate half cycles, C14 is charged to a

positive value via D12, and C13 is charged to a negative value via D11.

As the frequency reduces, the voltage at the anode of D13 becomes most

positive and at the cut off frequency, D13 begins to conduct, tuning off

VT4 for a period that increases as the frequency reduces further.

The collector of VT4 begins to pulse to a negative value, producing

pulses of current through R38, causing the output voltage of IC2a to

become positive. The effect of current flow through D15, D14, R43,

R42 and LK5 to the input of IC1 is to reduce the reference current at

IC1 input, thereby causing a reduction in the level of controlled voltage,

to a value depending on the frequency of the generator. LK3 and LK4

select the knee point (the frequency at which the over. flux circuit

begins to operate). An additional feed is taken from TP4 via R76 and

D25, which is used to inhibit the action of the under voltage monitor

when the over flux protection is operating, and R49 is used to inhibit

the diode failure detector when the over flux protection is operating.

4.2.7 Diode Failure Detector

Diode or fuse failure in the rotating assembly is detected by sensing

ripple induced in the exciter field current, caused by misbalance load

on the exciter output.


47�

The voltage from the stabilizing resistors (R1, R2 on back panel) is

supplied to the diode failure circuit where it is attenuated and smoothed

by R57, RV6 and C16. This signal, which now represents

approximately 80% of the average input, is fed to the inverting input of

IC2c. The input signal is also fed via R55, with minimal smoothing by

C18, to the non-inverting input of IC2c. The output of IC2c is

normally high and goes low only when the negative peaks of the

unsmoothed input fall bellow 80% of the average input signal. The

output of IC2c is fed via D18 and R61 to the input of IC2d that turns on

VT5 after a time delay generated by R64 and C20, zeners Z4 and Z5

clamp the output of IC2d. VT5 turns on VT6 energizing the back panel

mounted diode or fuse failure relay via D21, LED1, LK7 and 28.

Pressing PB1 that injects current via R56 to the input of IC2c tests the

detector. The light emitting diode LED1 provides local indication that

the detector is operating


48�


49�

If local indication only is required, LK7 should be removed and

R69 fitted. In the majority of applications the fixed sensitivity described

above will be suitable. This standard sensitivity will accept a normal

negative going peak ripple of 20% of the D.C. level.

LK12, when fitted, provides adjustable sensitivity from

approximately 20% to 12% of the D.C. level, sensitivity increasing as

RV6 is turned clockwise.

LK13, when fitted, provides adjustable sensitivity from

approximately 20% to 40% of the D.C. level, sensitivity being reduced

by turning RV6 clockwise.

4.2.8. Soft start circuit

When the generator is run up with the excitation switched on,

voltage will build up slowly due to the falling frequency circuit. A

circuit is incorporated which limits the rate of rise of output voltage,

when the excitation is applied suddenly at rated speed by closing the

field contractor or switching on the PMG supply.

Assume that the set is running which the MAVR energized but the

field contractor open. The auxiliary contact on FAC (across 2/5 and

2/11) is open and RL1 is de-energized. The MAVR is energized but

since RL1-1 is open, the voltage across C23 is low, D23 and D24 being

reversed biased. VT7is turned on by R70 and current flows through

R74 and (25) to prevent operation of the under voltage monitor.

RL1-1 closes and the voltage at TP7 become positive, returning to

the negative rail potential as C23 is charged through R73. During the

period that TP7 is positive, a transient current flows through and the

under voltage monitor (if fitted) is inhibited by a transient current

through D24, R75 and (25).

If FAC is initially closed and excitation is applied by switching the

PMG output to the MAVR, the transient feeds through D23 and D24

occur in the same manner since the initial charge on C23 is zero, and


50�

RL1-1 will close, when the MAVR is energized.

In both cases, VT7 is turned off during normal running due to

RL1-1 being closed.

If for any reason, the auxiliary contact on FAC is not used to

provide soft start, multi-cores 2/5 and 2/11 should be linked.

4.2.9. Three Phase Sensing

When this option is included the C phase sensing voltage is

supplied to D1, D2 via (5) and to cater for the increased input voltage,

link LK9 should be removed.

4.2.10. Link Identification

LK1 Selects transient feedback from exciter field current as

used for stabilisation on brushless generators.

When fitted LK2 must be omitted.

LK2

Selects transient feedback from the error amplifier

output as used for stabilisation on statically excited

generators.


LK3 Selects falling frequency knee point at 42.5Hz for 50Hz

generators.


LK4 Selects falling frequency knee point at 51Hz for 60Hz

generators.


LK5 Selects falling frequency circuit operation.

LK6 Selects field current limit circuit operation.

LK7 Selects diode failure detector circuit operation.

LK8 Selects soft start circuit operation.

LK9 Selects single phase sensing. When removed the unit is

suitable for three phase sensing.

LK10 Selects the normal level of field current limit.

LK11 Selects a field current limit level of one tenth of the

normal level (used during commissioning).


51�

LK12

LK13

Not normally Fitted

LK12 brings RV6 into operation to increase sensitivity,

i.e. circuit will operate with a lower level of ripple.

LK13 brings RV6 into operation to decrease sensitivity,

i.e. circuit will operate with a lower level of ripple.


This section describes the commissioning procedure for the control

card and should be read in conjunction with the general commissioning

procedure, section 13 and any specific contract commissioning

instructions.

IMPORTANT:

(1) The short circuit field current limit potentiometer, IFLIM, has

been set to the correct level at the factory and should not require

any on-site adjustment.

(2) Check that the correct links are fitted as detailed in the Setting

Records for MAVR tested with test generator (sub-section 6).

(3) Check operation on hand control prior to operation in auto

control.

4.3.1 Basic voltage control and soft start circuits

Set the mainframe front mounted motorized voltage setting

potentiometer to mid rang and the control card ‘Set V’ control fully

anti-clockwise.

Run the generator up to rated speed and switch the excitation to

‘auto’ control. The generator voltage should up slowly, due to the soft

start circuit action, to a stable voltage below nominal.

If the generator voltage is unstable the stabilizing controls should

be adjusted as described in sub-section 4.3.6. Adjust the ‘set V’

control to bring the generator voltage to its nominal value. Check by


52�

rotation of the motorized voltage setting potentiometer that the

generator voltage can be varied by ±10% from its nominal value and

reset it to this value.

Switch off the excitation for 2 minutes to allow the soft start circuit

to reset. Check that on re-selecting ‘auto’ excitation control the

generator voltage builds up slowly to nominal with minimal overshoot.

4.3.2. Falling Frequency Circuit

Inhibit any speed switch signal, where applicable, to maintain

‘auto’ excitation control at reduced frequency.

Reduce the generator speed and check that line voltage is reduced

in sympathy with the generator frequency below 85% of nominal

frequency. Run up set from low speed with the excitation switched on.

Check voltage builds up at approximately 40% speed and increases

gradually to nominal when 85% speed is reached.

4.3.3. Parallel Operation

To ensure reactive load sharing between AVR controlled generators

operating in parallel and to ensure stable control when paralleled to a

large supply system, it is necessary to provide quadrature current

compensation (Q.C.C.). Q.C.C. is phase sensitive and it is necessary to

carefully check the phasing of the sensing voltage and current to the

contract schematic diagram.

When synchronizing the generator for the first time the procedure

shown below should be followed: -

1) Synchronizing to a large supply system:

Set the Q.C.C. (RV1) control fully clockwise and carefully

synchronies are ensuring minimal mismatch in system and

generator voltage. Increase the motorized voltage setting

potentiometer and check that a lagging KVAR load is taken on the

generator.

2) Synchronizing to another generator:-


53�

Connect the other generator to the bus-bars with hand controlled

excitation and synchronies to it the set being commissioned with

‘auto’ excitation to give 25% reactive circulating KVAR. The

bus-bar voltage should reduce by approximately 4%.

3) Set the Q.C.C. control, i.e. RV1, to give the required droop.

4.3.4. Diode Failure Circuit

1) Check that the diode failure test pushbutton gives local LED

indication after approximately 2 seconds delay. The generator

should be operating on no load, with MAVR operation. If possible,

fully load generator at rated power factor and check that no diode

failure indication is given.

2) To be certain that the diode failure relay operates. When a rotating

diode failure occurs the most appropriate test is to temporarily

replace one of the brushless rectifier fuses by an open circuit (blown)

fuse (N.B. it is essential on high-speed machines to maintain

mechanical balance by fitting an equivalent fuse). Run the

machine and excite an open circuit at nominal volts. Indication of

diode failure should be given. On identical machines it is

acceptable to perform this test on one machine only. Do not

attempt this test unless the blown fuse is a direct mechanical

replacement to the healthy one.

3) In unusual cases, the inherent ripple in exciter field current may be

too high under healthy conditions, and the relay may operate

continuously, In this case fit LK13 and rotate RV6 clockwise from

the fully anti-clockwise position until the relay de-energizes.

Rotate RV6 two further turns clockwise. In this case it is

recommended that the test in (2) above be performed to confirm

relay operation on an actual fault.

4) In the unlikely event of the test in (2) above not resulting in

operation of the relay, fit LK12 and increase the sensitivity of the


54�

relay by rotating RV6 clockwise from the fully anti-clockwise

position until the relay operates, then rotate RV6 two turns further.

4.3.5 Field Current Limit Circuit

This circuit is incorporated to limit the steady state short circuit

fault current to a defined safe level and has been preset at the factory to

be required level. It should not be altered unless absolutely necessary.

If the level needs to be reset or checked this can best be achieved at low

excitation levels on open circuit as follows: -

Remove LK10 and fit LK11. In this state the If limit circuit will

operate at one tenth of its normal level. Set RV5 to give a limiting

excitation level one tenth of the desired level and finally remove LK11

and replace LK10.

4.3.6. Stabilizing Circuit Adjustment

The stabilizing controls are: -

Set Q – Quantity or magnitude of stabilizing signal (RV4)

Set P – Phase of stabilizing signal (RV3).

If it is necessary to adjust the stabilizing the following procedure

should be carried out:

1) Adjust ‘set P’ to 10 turns clockwise and ‘Set Q’ to 15 turns

clockwise.

2) With the generator running at rated speed, select ‘auto’ excitation.

The voltage should build up and stabilize.

The generator voltage must now be disturbed by means of suddenly

changing the setting of the motorized voltage setting potentiometer or

operating PB2 the ‘STEP’ pushbutton after fitting the control card

into the rack using the extender card.

3) If the voltage recovery is sluggish, turn ‘Set P’ anti-clockwise by a

small amount. Reset ‘Set q’ by turning it anti-clockwise until the

voltage becomes unstable and then clockwise until just stable.

4) If the voltage recovery is oscillatory, turn ‘Set P’ clockwise by a


55�

small amount. Reset ‘Set Q’ as in (4).

5) Having optimized the stability to voltage reference changes it

remains to finally optimize the response by load application and

rejection. Repeat step (4) and (5) using load changes until the

optimum is reached.

Optimum stabilizing is achieved when the voltage overshoots the

final steady value once following load application.

The response as indicated by the generator output voltmeter would

be affected by the damping of the meter movement. A more

accurate indication can be obtained from a multi-meter connected

across the exciter field.

If definite recovery time following a particular load change should

not be exceeded, an oscillogram of generator output voltage should be

taken on a suitable recorder having a high frequency response.


This section describes the faultfinding procedure for the Control

Card and should be read in conjunction with the general fault finding

section 14.

IMPORTANT

1) The majority of excitation faults are caused by incorrect

connections – thoroughly check all connections are correct to

0NQ.359.019 Excitation System Circuit Diagram.

2) Check that the correct links are fitted as detailed in the setting

records for MAVR tested with test generator, sub-section 6.

In general faults associated with the Control card can be separated

into four categories, viz.

1. Over Excitation (Table 4-1)

2. Under Excitation (Table 4-2)

3. Instability (Table 4-3)


56�

4. Operational Faults (Table 4-4)

Refer to the appropriate section for corrective action.

Table 4-1 Over excitation Faults

No. Possible Fault Test Remedial Action

1 Loss of voltage

sensing

Check FS3,4(&5)

and all external

fuses and wiring

Measure sensing

voltage (2/7 to 2/9)

on hand control

Replace blown fuses or

correct as necessary.

2 Q.C.C. Circuit

Failure

Check Q.C.C. feed

to 1/13 & 1/15

Correct as necessary

3 Mainframe

Failure

See mainframe

failure finding

procedure.

See section 2.4

4 Limiter Card

Failure

Remove Limiter

Card

See excitation limiter

card failure finding

procedure.

5 Auto Power

Card Failure

See Auto power

card failure

finding procedure.

See Auto power card

failure finding

procedure.

6 Control Card

Failure

Interchange

Control Card with

a spare

Replace Control Card

and return faulty card

to the Works for repair

Table 4-2 Under Excitation


1 Wiring Fault Check all external

wiring


2 Q.C.C. Circuit

Failure

Check Q.C.C. feed

to 1/13 & 1/15



57�

3 Loss of

Auxiliary

Power Supply

Check FS1&2 and

any external fuses

and wiring to

auxiliary supply.

Replace blown fuses or

correct as necessary.

4 Mainframe

Failure

See mainframe

failure finding

procedure.

See Section 2.4

5 Limiter Card

Failure

Remove Limiter

Card

See Section 6.4

6 Auto Power

Card Failure

See Auto power

card failure

finding procedure.

See Section 5.4

7 If Limit too

low/faulty

Remove link 6 Reset as in Section 4.3.5

or if faulty repair

Control Card

8 ‘Frequency Fall

Off’ circuit

operating

Remove link LK5 Check correct links

fitted, if faulty repair

Control Card. Check

capacitors C11&12 on

Control Card are

correct.

9 ‘Soft Start’

Circuit faulty.

Remove Link LK8 If correct with LK8

removed, repair control

card.

⒑ Pilot exciter

faulty

Check Pilot exciter

output

Check and repair pilot

exciter

⒒ Control Card

Failure

Interchange

Control Card with

a spare

Replace Control Card

and return faulty card

to the Works for repair

Table 4-3 Instability



58�

1 Incorrect

stabilizing

circuit link

selected.

Check LK1 is

fitted for Brushless

generators, or LK2

fitted for directly

excited generators.

Select correct link.

2 Incorrectly set

Stability

controls.

See Section 4.3 See Section 4.3

3 Main-frame

faulty

No field current

pick up signal to

control card

(1)&(29)-should be

150 mV to 1V 0n

no-load.

See Section 2.4 & 3.4

4 Power System

instability

Refer to operating

chart to ensure

stability limits are

not exceeded.

Check stability of

excitation limiters if

operating.

5 Governor

instability

Check excitation

stable on hand

control

Reset governor

stabilizing…

Table 4-4 Operational Faults

No. Symptom Possible Fault Test Remedial

Action

1 Over fluxing at

reduced speeds

Frequency

Fall Off

Circuit faulty

or link LK5

omitted/incor

rect Lk3/4

fitted

Check LK5

is fitted and

LK3 for

50Hz or

LK4 for

60Hz set.

Fit Link 5, if

omitted or

repair

control card


59�

2 Limited lagging

capability or

sluggish

on-load

response

If limit set too

low or faulty

Check again

after

removing

LK6

Reset level

as in Section

4.3 or if

faulty repair

Control

card.

3 Diode failure

indication

permanent-ly on

Diode has

failed DFI too

sensitive or

faulty

Check

rotating

diodes or

DFI

sensitivity

Refer to

Section 4.3

Replace

faulty diode,

reset DFI

sensitivity or

repair

control card

if faulty

4 Diode failure

circuit in

operative

LK7 is

omitted or

R65 is not

fitted. DF1

not sensitive

enough.

Check LK7

or R65 is

fitted

Fit LK7or

R65. If still

faulty repair

control card

5 Excessive

overshoot on

excitation

build-up

Soft Start

Circuit is

faulty, LK8 is

omitted, or

external

wiring is

incorrect

between 2/5

and 2/11.

Incorrect

stabilizing

adjustment.

Check as

necessary

Correct as

necessary


60�


61�

5. AUTO POWER CARD

5.1 SPECIFICATION

5.1.1 Maximum continuous ratings within the temperature range : 25℃ to

+50℃:

(1) 50 Hz to 576 Hz (i.e. to 480 Hz +20% over speed).

(2) 15A D.C. output (12.5A at 65℃).

(3) 350 volts RMS input at +20% over speed, open circuit.

5.1.2 In addition, to meet short circuit excitation levels, the following rating

applies for 3 seconds maximum: 25A D.C. output.

5.1.3 Storage temperature range: -40℃ to +100℃

5.1.4 Maximum (D.C.) output volts =RMS input volts ×0.9.



connections).

The PMG excitation source is supplied to the half controlled

thyristor bridge, THB1, via the fuse, FS1, at (6)(7)(8)(9)(10) and

(20)(21)(22)(23)(24).

The thyristor control signals, coming from the control card, are

supplied to (12) (13) for SCR1 and (14) (15) for SCR2. The phasing of

these control signals with respect to the PMG voltage varies the mean

D.C. output of the bridge which appears at (1) (2) (3) (4) (5) positive

and (25) (26) (27) (28) (29) negative.

The two resistors R1, R2, are incorporated to ensure a low

impedance gate circuit to avoid false thyristor triggering due to pick-up.

The suppressor, CL1, is fitted to protect the bridge against spurious

voltage transients.


This section describes the commissioning procedure for the auto


62�

power card and should be read in conjunction with the general

commissioning procedure, section 11 and any specific contract

commissioning instructions.

As the auto power card converts the output of control card into the

required generator excitation the commissioning procedure follows that

of the control card. As a precautionary measure check that the fuse,

FS1, and the half-controlled thyristor bridge, TM1, DM1, connections

are physically sound.

5.4 FAULT FINDING PROCEDURE LT

This section describes the faultfinding procedure for the Auto

Power Card and should be read in conjunction with the general fault

finding section 12.

IMPORTANT:

(1) The majority of excitation faults are caused by incorrect

connections – thoroughly check all connections are correct to

the 0NQ.359.019 Excitation System Circuit Diagram.

(2) To reduce electrical stress on the edge connectors, if at all

possible the power cards should only be withdrawn with the

generator unexcited, or being controlled by a standby AVR.

If it is absolutely necessary to remove an auto or hand power card from

a MAVR, which is in use, first select the alternative card.

Never withdraw a card that is supplying excitation since this may

damage the connections.

Table 5-1 AUTO POWER CARD FAULTS

No Symptom Possible Fault Test Remedial

Action

1 No

excitation

a) Control Card

Fault

b) FS1 failure

c) External fuse

See section 4.

Check FS1.

Check

external fuses,

See section 4

Replace, if

necessary, with

20ET fuse


63�

failure, wiring

fault, or pilot

exciter failure.

d)Field circuit

incomplete

e)Thyristor bridge

failure

wiring and

pilot.

Check field

continuity.

Check TM1 &

DM1 bridge as

detailed below.

link.

Replace/correc

t as necessary.

Correct as

necessary.

Replace card if

faulty

2 Over

excitation

a) Control Card

Fault

b) Thyristor

bridge failure

c) Wiring fault

See section 4

Check

thyristor

bridge as

detailed below.

Check wiring

See section 4

Replace card if

faulty

Correct as

necessary

THYRISTOR BRIDGE TESTS

The thyristor bridge consists of TM1 thyristors and DM1 diodes

mounted in an encapsulated module. The drives can be individually

checked however with the unit assembled on the card (withdrawn from

the mainframe) as described below.

1) Thyristors

Connect the circuit as shown:

(1) Initially, with the switch S open and not having previously been

closed, ensure that the ammeter registers zero current.C

(2) lose S and observe that the ammeter now registers

approximately 3/4 amp.

(3) Re-open S and observe that the ammeter continues to register

–ideally as in (b) above.


64�

Figure 5-1 thyrisistor Test Circuit

If any one of these three tests is not satisfied for the thyristor,

the Auto Power Card should be replaced.

N.B. To reduce the current to zero after the thyristor has been

triggered-as in (b) above – the battery circuit must be disconnected.

2) Diodes

The diodes can easily be checked by measuring the forward

and reverse resistance, with an ohmmeter e.g. AVO meter model 8

etc.

Each diode should exhibit a low resistance in the forward

direction, typically 20-50 ohms, and a very high resistance in the

reverse direction.

If either diode has zero or wary low resistance in both

directions or infinite or very high resistance in both directions, it is

faulty and the Auto Power Card should be replaced.


65�


66�

6. EXCITATION LIMITER CARD.

6.1 SPECIFICATION

6.1.1 Over Excitation Limiter

1) Limiting level

The limiting level is adjustable within the range 5 to 15 A in the

brushless system or an input voltage of between 0.8 and 2.5 volts in the

case of a static excitation scheme.

2) Increased Sensitivity feature

An internal link enables the sensitivity to be increased by a factor of

4 (±2.5%) to allow setting up without overexciting the generator.

3) Temperature Compensation Facility

By use of an external 100 ohm or 130 ohm Resistance Temperature

Detector (RTD) situated in the machine air inlet, temperature

compensation may be achieved.

Compensation temperature range –25 ℃ to +55 ℃ (RTD

temperature).

Compensation level –0.2 to –1% of O.E.L. level/℃ rise.

Compensation Characteristic ±1% linearity.

Providing that.

(1) The local ambient temperature is within 15℃ of that at which

the unit was set.

(2) The ideal RTD characteristic i.e. linear and having a

39.2x0.0001 p.u/℃ temperature coefficient.

(3) The RTD has 3 lead termination, the individual lead resistance

being less than 50 ohm.

4) Differential Feature

Two links can be selected: one selects 80% (±2.5%)differential, the

other 70%(±2.5%) differential. Dependent upon which link is selected,

the limiter will control excitation to 70% (or 80%) of nominal limiting


67�

level and only reset when excitation reduces below the controlled level.

The feature will normally be inhibited by an internal link.(100%

differential).

5) Time Delay

An adjustable ‘integrating delay’ is incorporated giving delays from

1000%-seconds to 100%seconds. This corresponds to a range of 10 to 1

seconds for a 100% error, i.e. excitation twice the nominal limiting level.

6) Temperature Range

-25℃ to +65℃: Operating

-40℃ to +100℃: Storage

7) Accuracy

Limiting level ± 2%

repeatability

Time delay ± 5%

repeatability

Provided temperature is within ±15℃

of the temperature at which the unit

was set, and with no temperature

compensation.

6.1.2 Under excitation limiter.

1) Characteristic

(1) MVAr limit at Zero power, this is set by the ‘Xd’ control. When

the input voltage and current supplied to unit are nominally

105V and 5A the ‘Xd’ control gives a MVAr limit ranging from

12.5% to 100% of the rated MVA. This is equivalent to a

generator reactance range from 8 to 1 p.u.

(2) Limiting Level Curvature, this is set by the ‘Xe’ control. When

the input voltage and current supplied to the unit are nominally

105V and 5A the ‘Xe’ control compensates for external

reactance effects (e.g. unit transformers) in the range 0 to 0.8

p.u.

2) Stabilization

Two controls are incorporated for stabilizing : quantity and phase


68�

For a brushless generator the limiter is stabilized from exciter field

current whilst for

a static excitation system stabilizing is obtained from the error

amplifier output.


-25℃ to +65℃: Operating

-40℃ to +100℃: Storage

4) Accuracy

Limiting level: ± 2%

repeatability

Provided temperature is within

±15℃ of that at which the

unit was set.

5) Input Signals

6) It requires a 5A current transformer input of 1 VA rating in the

blue phase. The voltage sensing is derived from the red to yellow

sensing signal.


1) Set Q: A front access multi-turn potentiometer which adjusts the

stabilizing signal magnitude of the under excitation limiter.

2) Set P: A front access multi-turn potentiometer which adjusts the

stabilizing signal phase of the under excitation limiter.

3) OE Delay: A front mounted, single turn potentiometer with a

calibrated dial scaled 0 to 10 which adjusts the time delay of the

over excitation limiter.

4) Set Xd: A front mounted, single turn potentiometer with a

calibrated dial scaled 0 to 10 which adjusts the operating level of the

unit at zero power.

5) Set Xe: A front mounted, single turn potentiometer with a

calibrated dial scaled 0 to 10 which adjusts the curvature of the

limiter characteristic.


69�

6) Set If: A front access multi-turn potentiometer which adjusts the

over excitation limiter field current limit.

7) Set Bal.: An internal access multi-turn potentiometer which

adjusts the temperature compensation bridge balance point.

8) Set T.C.: An internal access multi-turn potentiometer which

adjusts the temperature compensation range.(i.e. effective

compensation achieved in %/℃)

9) OE On: A front mounted ‘Light Emitting Diode’ to give

indication of the over excitation limiter.

10) UE On: A front mounted ‘Light Emitting Diode’ to give indication

of operation of the over excitation limiter.

11) Relay output: For remote indication of an over or under excitation

limiter operating condition a common relay mounted in the

Mainframe in energized.


(Number in brackets ( ) refer to p.c.b. edge connections, and all

voltage levels are relative to TP1.)

6.2.1 Over Excitation Limiter

(This is shown on the lower half of the Schematic Diagram Fig 6.4)

On a brushless excitation system field current is sensed across the

MAVR stabilizing resister, R1, R2 mounted on the back panel, and the

signal is supplied to the limiter at (2) and (29).

On a static excitation system the signal is derived from a DC

current transformer measuring rotor current.

A current proportional to the field current is compared to the

stabilized reference current flowing through R56. When the field

current exceeds a preset level determined by the reference current and

the setting of RV5, the output voltage of IC3b begins to fall, and when it

becomes negative current flows through R65, D20, LK12 and (15),


70�

reducing the change rate of C6 on the control card thereby reducing the

excitation.

IC3a and associated components provide the temperature

compensation facility. The external RTD is the temperature sensor in a

detector bridge (comprising R39, R42, R43, R70 and RV8) RV8

adjusting the balance points of the bridge. Components Z4, R40, R41,

FS1 and D26 are the stabilized power supply for the detector bridge.

The misbalance of the bridge, which bears a direct relation to the

temperature change, is amplified by IC3a and effects the limiter

reference current via RV7, R55 and LK5. Adjustment of RV7 alters the

degree of compensation achieved. To facilitate commissioning of the

unit links I3, I4, I5, I6, I7 are used to test the temperature compensation,

catering for both 100 ohm and 130 ohm RTD’s at both 0℃ and 40℃.

Removal of LK5 inhibits the temperature compensation circuit effect.

IC3a output is routed to the excitation monitor card via (25) to provide

temperature compensation on that card if required. In general in the

generator with closed cycle ventilation system, the temperature

compensation unit should not be used.

If the RTD fails and shorts to earth, to protect the operation of the

limiter THY1 is ‘fired’ by D31, D30, D29 (depending on Fault location),

Z9 and R86, This momentarily shorts the supply rail rupturing FS1,

therefore disconnecting the supply to the detector bridge. IC3a output

rises to 6.2V. It is clamped by Z8 which corresponds to an RTD

temperature of about 55℃.

When the voltage at TP6 become negative transistor VT6 is turned

on via R45, and if LK9 or LK10 is fitted, part of the reference current is

diverted through VT6. Thus, the field current can be limited to a level

lower than that required to cause the limiter to operate.

Either LK11, LK10 or LK9 may be fitted (one link only) which will

make the limiting level 100%, 80% or 70% of the operating level


71�

respectively.

As a commissioning aid the sensitivity of the limiter can be

increased by fitting LK7, which reduces the reference current and the

operating level of the limiter by a factor of four. The differential links

LK9 or LK10 should be removed when using this facility, as should the

temperature compensation link LK5.

Indication of limiter operation is provided by IC3c output going

positive. TP6 voltage becomes negative .VT3 and VT4 are switched on

and an output signal via LED2 and D23 provides local indication and

energizes RL1 in the back panel via(17) providing remote indication of

limiter operation. The integrating time delay is provided by C10 and

RV6.

On the standby AVR of a twin AVR system the output of the OEL

amplifier TP6 is disconnected from the OE delay control by RL1-1, and

the voltage on the delay circuit is linked via RL1-1, (18) on the standby,

to the output of the controlled limiter via the back board and (23) on

the controlling limiter. This is to prevent surges in excitation due to the

high gain of standby and controlling limiters when control is switched

to the standby unit.

Twin System with Differential Facility

When transferring control to a standby AVR from a unit with its

over excitation limiter operating, a transient surge in excitation may

occur since it may be necessary to allow the excitation to reach the

standby limited operating level, prior to excitation being reduced to the

controlling level.

6.2.2 Under Excitation Limiter

This is shown on the upper half of the schematic diagram. Fig 6.4.

The under excitation limit of a generator operating in parallel with a

system is determined by the generator and system reactance, and can be

represented on the generator operating chart. Figure 6.1 shows a typical


72�

operating chart and the effect of differing external reactance between

the generator and the infinite systems. Such a system could be due to

transformers

Figure 6-1. Generator Operating Chart

If the excitation is reduced to a level that wound cause the

generator to operate at a power factor more leading than is shown on

the chart, the angle by which the internal emf of the generator leads the

system voltage will exceed 90°and loss of synchronism may occur.

So that the operation of the limiter can be understood, it is necessary to

be aware of the relationship between the simplified vector diagram of

the generator and the generator operating chart.Figure 6-2 below shows

the equivalent circuit and vector diagram of the generator paralleled to

an infinite system.

I = generator current

Et = generator terminal emf

Vt = generator terminal voltage

eIXIXtEV d


73�

V∞ = system voltage

Xd = generator synchronous

Xe =external reactance

Fig 6-2 The simplified Vector Diagram

The condition is drawn for line current Ⅰ，at Φ leading. The

under excited limiter occur when the internal Emf, Et. Leads the

voltage of the infinite system by 90°。

It can be seen that when Xe=0, the limit is a straight line

corresponding to constant leading VAr’s of 1/Xd per unit, and that as

Xe increases the MVAr limit reduces with increasing power.

The under excitation limiter incorporates circuits in which the

internal emf of the generator and the system voltage， are simulated

and a control signal is produced to maintain the excitation above a level

that would cause the 90° load angle to be exceeded.

Operation

(All voltage levels are relative to TP1).

The unit senses line voltage at (21) (29) which is nominally 2.5 volts

rms supplied from T1 on the back panel, and line current at (28) (27)

nominally 28mA supplied by T5 on the back panel. The phasing of these

signals is such that the current leads the voltages by 90°when


74�

generating at unity power factor.

The input circuit compressing R1, R5, R9, RV1, RV2, is arranged

so that voltages corresponding in phase and amplitude to the internal

emf of the generator, and the system voltage are produced at TP3 and

TP4 respectively. IC1a, IC1b, IC1c, and IC2 form a circuit which

produces a mean positive voltage across C3 when the voltage at TP3

leads that at TP4 less than 90℃, and a mean negative voltage when

the voltage at TP3 leads that at TP4 by more than 90°.

The latter case corresponds to an under excited condition, current

through R19, causing the output of IC1d to rise producing a signal

which is fed to (15) on the control card via D9, R25, LK6 and (15). The

operation of the limiter is to ensure that C6 on the control card is

changed fast enough to prevent the field voltage from being reduced a

level that would correspond a load angle in excess of 90°.

It is necessary for the limiter to respond rapidly to an under excited

condition and therefore stabilizing is required which is achieved by

transient feedback via R22, RV3, RV4, and C6. The stabilizing signal is

obtained from exciter field current (via LK4 and (2)) on a brushless

AVR, and from the output of IC1d (via LK3) on a static excitation

system. Local indication of limiter operation is provided by LED1 and

RL1 on the back panel (via 17) which operate when VT1 and VT2 are

turned on by the output of IC1d.

CMOS QUAD Solid State Switch (4016) IC2

This is a 14 pin package which contains four solid state switches.

Consider one switch; when a positive voltage is applied to say pin 5, the

signal present at pin 4 is internally connected to pin 3. Thus, with pin 5

positive, 4 and 3 can be considered as a closed switch, and with pin 5

negative, 4 and 3 can be considered as an open switch.

6.2.3 Link Identification

Link LK1 Fitted for 100 ohm RTD. When fitted omit LK2


75�

Link LK2 Fitted for 130 ohm RTD. When fitted omit LK1

Link LK3 Selects transient feedback for the under excitation limiter

from the amplifier output. This is used for stabilization on statically

excited generators. When fitted LK4 must be omitted.

Link LK4 Selects transient feedback for the under excitation

limiter from exciter field current as used for

stabilization on brushless generators. When fitted LK3

must be omitted.

Link LK5 Selects temperature compensation on the over

excitation limiter.

Link LK6 Selects the under excitation limiter relay outputs.

When fitted LK6A must be omitted.

Link LK6A Inhibits the under excitation limiter relay outputs.


Link LK7 Selects an increase of sensitivity by a factor of 4 on the

over excitation limiter for commissioning purposes

only.


Link LK8 Selects the normal operating sensitivity of the over

excitation limiter. When fitted LK7 must be omitted.

Link LK9 Selects 70% differential on the over excitation limiter.

When fitted LK10 and LK11 must be omitted.


When fitted LK9 and LK11 must be omitted


When fitted LK9 and LK10 must be omitted

Link LK12 Selects the over excitation limiter relay outputs. When

fitted LK12A must be omitted.

Link

LK12A

Selects the over excitation limiter relay outputs. When

fitted LK12 must be omitted.

Link LK13 Test facility for 130 ohm RTD at 0℃.Not normally

fitted.


76�


fitted.


fitted.


fitted.

Link LK17 Test facility for temperature compensation. Not

normally fitted.

Link LK18 Fitted for normal operation.

6.3 COMMISSIONING PROCEDUCE


excitation limiter card and should be read in conjunction with the

general commissioning procedure, section 9, and any specific contract

commissioning procedure.

IMPORTANT

(1) The potentiometers, ‘OE Delay’, ‘Set If’, ‘Set Xd’, ‘Set Xe’, ‘Set

TC’ have been set to the correct level at the factory and should not

require any on site adjustment.

(2) Check that the correct links are fitted as detailed in the setting

record for MAVR testing with test generator sub-section 6.

(3) Complete commissioning of the control card prior to commissioning

the excitation limiter card. Temporarily remove the Excitation

Monitor card, if fitted, to avoid transfer of excitation to another

source.

6.3.1 Over Excitation Limiter –X4 Level

(1) Determine the limiter parameters, (over excitation limit X1 and

X4, differential, delay and temperature compensation) from

setting record for MAVR testing with test generator sub-section

2. In the absence of these, typical settings are the X1 limit 10%


77�

higher than the continuous full load rating of the exciter : the

differential to 100% (link 11): the time delay to 400% seconds:

and the temperature compensation to 80% of the 0℃ level for a

temperature rise of 40℃.

(2) Remove limiter card and re-insert together with the extension

card, Fit link LK11 and remove LK9 or LK10 if applicable, and

LK5.

(3) Select the X4 increased sensitivity feature by removing link LK8

and fitting LK7, thereby enabling the approximate operating

level of the unit to be checked at a low excitation level. Insert a

suitable ammeter in the field circuit if one is not already

available.

(4) Run the generator up to rated speed, unparalleled, and on

no-load with ‘auto’ excitation selected.

(5) Check that no external limiter operation signal is given(i.e. an

open circuit between outgoing multicore 2 wires 8 and 10) and

the ‘OE On’ LED is off. This assumes that the no-load excitation

is less than 25% of the preset over excitation limit.

(6) Increase the excitation to above the preset 0℃ over excitation

limit divided by 4 (to allow for the X4 increase in sensitivity) by

adjusting the motorized voltage setting potentiometer fully

clockwise and if necessary the ‘Set V’ potentiometer on the

control card. The over excitation limit should operate (i.e. a

short circuit between outgoing multicore 2 wires 8 and 10,

together with the ‘OE On’ LED coming on), and control the

excitation to the required 0℃ limit divided by 4, after a

significant time delay - approximately 160 seconds for a 10%

error in field current or 4 times the required percentage -

seconds delay. Note the operation of the limiter will be

accompanied by a reduction in line voltage.


78�

NOTE:

If the no - load excitation is greater than 25% of the 0℃ over

excitation limit, the limiter will operate to reduce line voltage

below nominal. If this is the case check that the field current is

controlled to 25% of the required limit ±2.5%, and that the

'OE On' LED is illuminated and the appropriate external signal

given.

(7) If the controlled level is incorrect by more than ±2.5 then the

'Set If' potentiometer has been reset since the unit left the

factory and requires readjustment, To increase the over

excitation limit rotate the 'Set If' potentiometer clockwise and

vice versa.

(8) The over excitation limiter is now set to limit field current to

approximately the required level when the X1 sensitivity is

reselected by removing link LK7 and fitting LK8. This will

allow the control card to control the generator voltage which

can be reset by setting the motorized voltage setting

potentiometer to mid-range and adjusting the control card 'Set

V' potentiometer to give nominal line voltage.

1) Over excitation Limiter. Check on Temperature Compensation

Facility X4 Sensitivity.

When the temperature compensation facility provided on the

over excitation limiter is utilized the preliminary checks outlined

below should be carried out.

(1) Perform tests AI) to VIII) above.

(2) Remove links 1,2,18.Fit link 17.

Fit link 15 if the RTD resistance is 100 ohms at 0℃ or Fit link

13 if the RTD resistance is 130 ohms at 0℃.

(3) Connect a dc. voltmeter across TP16 (+ve) and TP1 and check


79�

that the meter indicates 0 volts ±0.25 volts, adjusting RV8

(set bal.) if necessary to obtain correct reading.

(4) Fit link 16 if the RTD resistance is 100 ohms at 0℃.

Fit link 14 if the RTD resistance is 130 ohms at 0℃.

(5) Determine from the setting record for MAVR testing with test

generator the percentage reduction in excitation for a 40℃ rise

(typically a 20% reduction) and check that the voltage

measured at TP16 (+ve) w.r.t. TP1 is equal to (% reduction in

excitation x 0.22) volts dc. ±15%. i.e. if the 40 ℃ limiter

setting is to be 80% of the 0℃ setting the reduction is 20% and

the voltmeter should read

(20 x 0.22) = 4.4 ± 0.66 volts dc.

Adjust RV7 if necessary to obtain the required reading .

(6) Remove links 17, 13, 14, 15, 16

Fit links 18 and 1 for a 100 ohm RTD

Or 2 for a 130 ohm RTD

(7) Check that the reading obtained on the dc. voltmeter connected

across TP16 (+ve) and TP1 corresponds to the ambient

temperature at location of the RTD.

The voltmeter should indicate

ambient temperature (℃) X Voltmeter reading in test (V)

40

(This test is not applicable at temperature below zero).

Fit link LK5.

6.3.2 Over Excitation Limiter -X1 Level

1) Synchronize the generator to the system and lightly load the

generator (5-10% of rated power). Connect a 10 volt dc voltmeter

(20 kohm per volt or more) across TP6 (+ve) and TP1, and check it

registers greater than 9 volts.

2) Gradually increase the excitation by clockwise adjustment of the


80�

motorized voltage setting potentiometer to an excitation level

approximately 5% over the recommended over excitation limit. The

voltmeter should indicate a slowly falling reading. When the meter

starts to read negative (approximately - 1 volt) the limiter should

come into operation and give local and remote indication. If

difficulty is encountered in reaching the required excitation level

rotate the control card 'Q.C.C.' potentiometer anti-clockwise.

3) If necessary trim the 'Set If' control to give the required excitation

limiting level; clockwise rotating increasing the limit and vice versa.

Reduce the excitation level to nominal.

6.3.3 Over Excitation Limiter - Differential

1) If 100% differential is required omit this section and proceed to

subsection 6.3.4.

2) Whilst still in parallel with the system and on the over excitation

limit select the appropriate differential link - LK9 for 70% and

LK10 for 80% (±2.5%) of the previous limiting level depending on

link selection- LK9 or LK10 respectively.

6.3.4 Over Excitation Limiter - Temperature Compensation (if applicable)

1) Leave RV7 (set TC) as set at the works and select or omit links as

follows:

100 ohm RTD fit LK15 & 17 omit LK1,2,13,14,16,18

130 ohm RTD fit LK13 & 17 omit LK1,2,14,15,16,18

Leave all other links as selected. Check RTD connections are

correct. Connect a 10V dc. voltmeter (20 kohm/v or more) between

TP15 (+ve) and TP1.

2) If necessary adjust RX8 (Set Bal.) to bring the voltmeter reading to

zero. Reconnect the multimeter to TP6 (+ve) and TP1.

3) Synchronize and lightly load the generator, increase the excitation

and check that the limiter operates as in section BII. Check that this


81�

limit is within ±1% of the required 0℃ over excitation limit.

4) Reduce the excitation to nominal and reselect links as follows:

100 ohm RTD Remove LK15 and fit LK16

130 ohm RTD Remove LK13 and fit LK14

5) Increase the excitation and check that the limiter now operates at a

lower level corresponding to the 40V over excitation limit ±2%, If

necessary adjust RV7 (Set TC) to achieve this, If no figure is

available for this limit assume a value of 0.8 x 0℃ Limit. Clockwise

rotation of RV7 increases the temperature compensation, i.e. reduce

the 40V Limit.

6) Reduce the excitation to nominal and reselect links as follows:

100 ohm RTD Remove Links 16&17 and fit Links 1&18

130 ohm RTD Remove Links 14&17 and fit Links 2&18

7) Increase the excitation and check that the limiter operates at a new

level dependant the external RTD temperature, 't'. Knowing this

temperature check that the limiter 'I' is

Where I0 = 0℃ limit I40 = 40℃ limit

If incorrect check the nominal RTD resistance and its connections

are correct.

6.3.5 Over Excitation Limiter - Time Delay

1) Whilst still in parallel with the system and on the over excitation

limit short out TP8 to TP1. This shorts out the over excitation

limiter sensing input so that the limiter resets - indicated by the

voltmeter resetting to above 9 volts - and excitation reverts to its set

level. Remove link LK9 or LK10, if fitted, and fit LK11.

2) Set the excitation to 'X%' above the over excitation limit

(preferably 10% or more - but at least 5%), Time the period taken,

't seconds', between removing the short between TP8 to TP1 and

%2}40

)({ 400

0

tII

II


82�

the unit limiting excitation. The product, 'X'x't', gives the over

excitation limiter time delay expressed in %-secs.

3) If necessary trim the 'OE Delay' control to give the required %-secs

delay; clockwise rotation increasing the delay and vice versa. When

rechecking the time delay allow the limiter to fully reset, i.e. the

voltmeter reading above 9 volts, before removing the shorting link

and retiming.

4) Refit the appropriate differential link LK9, 10 or 11.Rest the Q.C.C.

potentiometer to the required setting if it was adjusted. Reduce

excitation by turning the motorized voltage setting potentiometer

anti-clockwise to give unity power factor. Remove the voltmeter

between TP6 and TP1.

6.3.6 Under Excitation Limiter - zero Power Limit

1) Determine the under excitation limiter parameters ('Xd' And 'Xe'

levels) from the setting record for MAVR Testing with Test

Generator sub-section 2. In the absence of these reference should be

made to the generator operating chart, the 'Xd' control should be

set to 10% less leading VAr's than the machine capability and the

'Xe' control to any quoted external reactance figure or a safe level -

say 0.1 p.u. reactance, 'Xe' can also be measured by synchronizing

the generator to the system and adjusting the power to zero; by

nothing the per unit change in reactive loads (Q) for a given change

in system voltage (V p.u.) of say 0.05 p.u. caused by changing the

motorized voltage setting potentiometer, Xe can be calculated as:

To simulate an exact under excitation limit reference should be

made to Fig. 6-3 below. The limiting level is given by a circle:

..upQ

VXe


83�

Thus knowing the required circular characteristics center and

radius the two parameters 'Xd' and 'Xe' can be deduced.

Fig. 6-3 Under Excitation Limit Characteristic

2) With the machine running in parallel with the system on 'auto'

excitation, set the generator output power to zero. Reduce the

excitation by slowly rotating the motorized voltage setting

potentiometer anti-clockwise and check that the limiter operates

when the generator leading reactive power reaches the required set

level. Operation is indicated by the 'UE On' LED coming on and a

short circuit between multicore 2 wires 8 and 10. Check that the

limiter operation is stable and that a further reduction of the

motorized voltage setting potentiometer does not increase the

generator leading reactive power beyond the required limiting level.

Adjust if necessary the limiting level by adjustment of the 'Xd'

potentiometer, clockwise rotation decreasing the limiting level and

vice versa.

upXdXe

center

upXdXe

redius

.}}

11{

2

1

..}}

11{

2

1


84�

3) If the limit is unstable adjust the two stabilizing controls 'Set Q' and

'Set P' as necessary, but first ensure that the limiting level is within

the generators capability as this can give rise to apparent

instability (actually pole swinging) when the machines limit is

exceeded or even reached. In generator to stabilize the limiter

increase clockwise the 'Set Q' control and if still unstable turn the

'Set Q' control anti-clockwise.

To check the response turn the motorized voltage setting

potentiometer first clockwise (off the limit) and then quickly

anti-clockwise (onto the limit). The limiter should quickly come into

operation and settle with minimal oscillatory action.

6.3.7 Under Excitation Limiter -'Xe' Control

1) Take the generator off its under excitation limit and set to unity

power factor by clockwise rotation of the motorized voltage setting

potentiometer. Remove the excitation limiter card from the rack.

2) Knowing the required external reactance, Xe, calculate from the

following the required resistance of the 'Xe' potentiometer

R = 60 x 5(Xe p.u)/(1 p.u Sensing CT current)ohms

Where 1 p.u sensing CT current = rated current/Sensing CT ratio

(nominally 5A)

3) Check using a digital ohm-meter that the resistance between TP2

and TP4 agrees with that calculated. If it is 'incorrect adjust the

'Xe' control, clockwise rotation will increase the resistance and vice

versa. Replace the excitation limiter card after first removing the

extender card.

6.3.8 Under Excitation Limiter - Operating Characteristic

1) To check the operating characteristic throughout its range bring the

limiter into operation by turning the motorized voltage setting

potentiometer fully anti-clockwise and check the under excitation

limiter is operating. Increase the generators output power from


85�

zero to maximum and check that the reactive power is varied in

sympathy with power as indicated on the generator operating chart.

2) If the operating chart is not available or 'Xe' could not be check as

detailed in sub-section 6.3.7 the following procedure should be

adopted. Knowing 'Xd' and 'Xe' per unit values, calculate the

radius and center of the limiter circular characteristic as shown in

Fig. 6.3. Referring to figure 6.3 for any generator output power

'OX', the corresponding limiter reactive power 'XY', can be

calculated as follows:

Reactive power 'XY' p.u =

3) From the above calculations the theoretical and practical limiting

curves can be compared and errors compensated for by

appropriate adjustment of the 'Xd' and 'Xe' potentiometers.

In general the 'Xd' control sets the zero power limit and the 'Xe'

control the curvature of the characteristic.

NOTE: The generator operating chart is normally drawn for

operation, at nominal voltage, although the actual limiting curve of

the generator and system reduces in proportion to the square of line

voltage, and the limiter incorporates this characteristic.

If the limiter characteristic is being checked, the readings of MVAr

should be divided by (per unit volts) squared, at line voltages other

than nominal.


This section describes the fault finding procedure for the Excitation

Limiter card and should be read in conjunction with the general fault

finding section 10.

IMPORTANT

)().()( 22 CenterOApowerOXpurediusAC


86�


connections -thoroughly check all connections are correct to

0NQ.359.019 excitation system circuit diagram.


record for 'MAVR Testing with Test Generator', sub-section6.

In general faults associated with the Excitation Limiter Card can be

separated into two main categories (Over and Under Excitation Limiter)

viz:

Over Excitation Limiter - Inoperative (Table 6.4.1)

- Continuous operation (Table 6.4.2)

- Operational Faults (Table 6.4.3)

Under Excitation Limiter - Inoperative (Table 6.4.4)

-Continuous operation (Table 6.4.5)

-Operational Faults (Table 6.4.6)


Table 6.4.1 Over Excitation Limiter Inoperative

No Possible Fault Test Remedial Action

1 Incorrect output

link selected

Check link LK12 if

fitted and LK12A

omitted

Correct as

necessary

2 Loss of power

supply

Check FS1&2 and any

external fuses and

wiring to auxiliary

supply.

Replace blown

fuse or correct as

necessary

3 RTD short circuit

or associated

wiring fault

Remove LK1 or 2 and

check correct

operation. Check RTD

and wiring.

Correct as

necessary


87�

4 Mainframe failure No fired current

pick-up signal to

limiter cards(2)&(29) -

should be 0.165V/A -

sensing current - or

internal power supply

failure.

See 6

5 'Set If' control set

too high

Check level as in 6.3.2 Reset level, if

necessary, as in

6.3.2

6 Limiter card faulty Interchange Limiter

card with a spare

Replace limiter

card and return

to the works for

repair

Table 6.4.2 Over Excitation Limiter-Continuous Operation


1 Increased

sensitivity link

selected

Check link LK8 if

fitted and LK7

omitted

Correct as

necessary

2 'Set If' control set

too low

Check level as in 6.3.2 Reset level, if

necessary, as in

6.3.2

3 RTD open circuit

or an associated

wiring fault

Remove LK5 & check

correct operation.

Check RTD and

wiring.

Correct as

necessary

4 Control

card/sensing

failure saving rise

to an over excited

condition

See 4 See 4


88�

5 Mainframe failure Field current pick-up

signal excessive

(should be nominally

0.165V between (2)

and (29 ) per amp of

excitation).

See 3

6 Limiter card

failure

Interchange Limiter

card with a spare

Replace limiter

card and return

to the works for

repair

Table 6.4.3 Over Excitation Limiter - Operational Faults

No symptom Possible Fault Test Remedial

Action

1 Limiter

operates when

machine on

load

'Set If'

control set too

low

Check level as

in 6.3.2

Reset level, if

necessary, as

in 6.3.2

2 Limiter

operates

transiently on

load application

'OE Delay'

set too short.

Check level as

in 6.3.5

Reset delay,

if necessary,

as in 6.3.5

3 Operation at

high loads

causes leading

power factor

operation on

limiter

operation

'Set If' level

too low or

differential

link(LK9,10

or 11)

incorrect or

excessive

temperature

compensation

Check level,

temperature

compensation

and

differential

required as

detailed in.

Correct as

necessary


89�

4 Limiter

operates but

does not give

indication

Mainframe

failure

Limiter relay

faulty (RL1

on

mainframe)

Replace

relay RL1

5 Time delay can

not be

lengthened

Smooth

change over

circuit

permanently

energized

Check

external

wiring to 2/3

to 2/5

Correct as

necessary

6 Limiter level

too low at high

ambient.

Excessive

temperature

compensation

.

Check as

detailed in

6.3.4

Correct as

necessary

Table 6.4.4 Under Excitation Limiter - Inoperative


1 Incorrect output

link selected

Check link LK6 is

fitted and LK6A

omitted

Correct as

necessary

2 Loss of power

supply

Check FS1&2 and

any external fuses and

wiring to auxiliary

supply.

Replace blown

fuse or correct as

necessary

3 Mainframe failure Loss of sensing

signals(sensing volts,

2.5V,(21) to (29) and

sensing current, 22.5V

at 5A (27) to (28).

See 3

4 'Xd' and 'Xe'

controls set too low

Check level as in

6.3.6/7

Reset level, if

necessary, as in

6.3.6/7


90�


card with a spare

Replace limiter

card and return

to works for

repair

Table 6.4.5 Over Excitation Limiter-Continuous Operation


1 CT and/or PT

sensing phasing

incorrect.

Check to contract

circuit diagram.

Correct as

necessary

2 Control card

failure giving rise

to an under excited

condition

See 4 See 4


card with a spare

Replace limiter

card and return

to the works for

repair

4 Mainframe failure All other tests fail to

clear fault.

See 3

Table 6.4.6 Under Excitation Limiter - Operational Faults

No symptom Possible Fault Test Remedial

Action

1 Generator

loses

stability

before

limiter

operation.

Limiter level

set too high.

Check

operation level

as detailed in

6.3.6/7

Reset levels, if

necessary, as in

6.3.6/7


91�

2 Generator

unstable

on Under

Excitation

Limiter

operation

Stabilizing

controls

incorrectly set,

or too close to

stability limit

(pole swinging)

Check

stabilizing

controls and

correct link

fitted(LK4 for

Brushless, LK3

for Direct

excitation) or

check operating

level.

Reset

stabilizing

controls or

level.

3 UEL

operates

briefly

during run

up or

when

excitation

switched

on

Incorrect

settings of

UEL stability

controls

Reduce stab Q

setting &

increase stab P

setting

4 Under

Excitation

Limiter

gives

spurious

indication

on load

changes.

Stability

control not

optimized.

Check

stabilizing

control as in

6.3.6

In general

decrease

stabilizing Q

and increase P

consistent with

stability

5 Limiter

operates

but does

not give

indication

Mainframe

failure

Limiter relay

faulty (RL1 on

mainframe)

Replace relay

RL1


92�


93�

7. POWER FACTOR CONTROL CARD

7.1 SPECIFICATIONS

7.1.1 Range of Control

1) Power Factor Control:

0.6 PF lagging to 0.9 PF leading

2) Reactive Current Control;

100% rated current lagging to 50% leading

(rated current =5A)

7.1.2 Accuracy of Power Factor Control

The phase angle is controlled to within ±1°at full load current (5A)

and ± 5 ° at 20% rated current (accuracy being approximately

inversely proportional to current) provided:

1) The frequency is within ±10% of nominal.

2) The line voltage is within ±20% nominal.

3) The temperature is within ±15℃ of initial value.

4) The line current does not contain more than 2% harmonics.

5) The line voltage is free of even harmonics and does not contain more

than 10% required power factor.

6) Odd harmonics.

7.1.3 Accuracy of reactive current control

The reactive current is controlled to within ±2% of rated current

provided:

1) The frequency is within ±10% of nominal.

2) The line voltage is within ±20% of nominal.

3) The temperature is within ±15℃ of initial value.

4) The line current does not contain more than 2% harmonics.

5) The line voltage is free from even harmonics and does not contain

more than 10% odd harmonics.

6) The 'Motorized Volts Setting Rheostat' has sufficient range to give


94�

the required reactive current.

7) The line current is in excess of 10% rated.

7.1.4 Temperature Range:

-25℃ to +65℃ :operating

-40℃ to +100℃ :storage

7.1.5 Input Signals

The unit require a 5A current transformer input of 1VA rating in

the C phase. The voltage sensing is common to the 'Control Card' B to

A voltage sensing signal.

A normally open contact is required to bring the unit into operation

when the generator is parallel, and another to give a VAr shed signal (i.e.

control to unity power factor).

7.1.6 Operation Indication

Local Indication is given when the unit is in operation and when in

the VAr shed mode.

7.1.7 Mode Selection

Selection of 'Power Factor' Or 'Reactive Current' mode of

operation is made by selection of internal links.

7.1.8 Remote Level Control

The operation level in either mode can be controlled by an

externally mounted 5k.ohm,1watt potentiometer. Internal/external

control is selected by internal links.

When a remote potentiometer is used to set the operating level, the

internally mounted potentiometer acts a fine trim on the level set by the

remote potentiometer. This facility is used on twin AVR systems to

equalize the controlling point of standby and main power factor cards.


1) Level: A front mounted single turn potentiometer with a

calibrated dial scaled 0 to 10 which adjusts cosφ or Isinφ

(dependent upon the internal links selected).


95�

2) Slug : A front access multi-turn potentiometer which adjusts the

period between MVSR pulses.

3) PFC on: A front mounted 'Light Emitting Diode' to give indication

that the circuit is operating.

4) VAr shed: A front mounted 'Light Emitting Diode' to give indication

that the circuit is operating in the VAr shed mode.

5) Gain: A front access multi-turn potentiometer which adjusts

the pulse width to the MVSR.


(Number in brackets ( ) refer to printed circuit board edge

connections and voltage levels are relative to TP1).



nominally 28 mA supplied from T3 on the back panel.

The phasing of these signals is such that the current lag the voltage

by 90°when generating at unit power factor.

7.2.1 COMS QUAD Solid State Switch (4016,IC1,IC2)

This is a 14 pin package which contain 4 solid state switches.

Consider one switch, when a positive voltage is applied to pin 5, the

signal present at pin 4 is internally connected to pin 3.Thus with pin 5

positive, 4 and 3 can be regarded as a closed switch, and with pin 5

negative, 4 and 3 can be regarded as an open switch.

VT1 and 2 are switched on by alternate half cycles of the sensing

voltage producing gating signals at pin 5 and pin 6 of IC2. The switch

associated with pin 6 (IC2) is arranged to produce a gating signal to pin

13 (IC2) in antiphase to that at pin 5 (IC2).

The output of the detector at TP4 is proportional to Isinφ and is

zero at unity, negative at lagging, and positive at leading power factor.

This signal is smoothed by R23, C6 and R24, and compared to a


96�

reference current flowing through R25. The difference between the

detector output and the reference signal is amplified by IC3 whose

output is a d.c.. level which may be positive ,negative, or zero.

Consider an under excited condition where the output of the

detector exceeds the reference current through R25. The voltage at TP5

becomes negative reaching a level determined by R39,R41,R43, when

VT7,VT8 and RL4 are switched on. PFC card(1) (7) are linked

applying auxiliary d.c.. supplied to multicore 3/9 to the voltage setting

potentiometer motor via LK20 on the back panel.

When RL4 is energized, D13 becomes forward biased and a current,

dependent on the setting of RV3,flows through R30, If this current

exceeds the error signal, the voltage at TP5 will rise until VT7,VT8 and

RL4 turn off, at a point determined by R39,R41 and R42, and the

feedback through R30 is removed.

The overall effect is to produce a series of pulses which drive the

potentiometer motor to its optimum position with the minimum of

overshoot.

For a particular error,RV2 and C10 determine the delay before a

motor pulse is given and RV3 sets the pulse width for a certain setting

of RV2.

When an over excited condition exists the voltage at TP4 becomes

negative the output of IC3 becomes positive and the circuit associated

with VT5, VT6 and RL3 operates to pulse the potentiometer motor to a

lower position through PFC card (1) (7) and LK21 on the back panel.

The VAr shed facility is initiated by linking multicores 2/5 and 2/3 thus

applying the +15V supply to RL2 to RL2 via (10) and LED2 which

provides local indication.

RL2-2 close which reduces the referenced current to zero, which

corresponds to zero VAr’s. This facility can be used as a means of

reducing line current to zero prior to shutting down a set.


97�

The power factor controller is switched into operation by linking

multicore 2/5 and 2/1. This energizes RL1 on the power factor

controller via (9) and LED1 which provides local indication.

7.2.2 Remote Latch and Reset Facility

By fitting the appropriate links and external connections, the power

factor controller can be switched out of service an operator attempts to

adjust the voltage setting control during parallel operation.

Back panel relay RL4 is energized via D11 or D12 when a voltage

raise/lower signal is applied to multicores 1/9 or 1/12.

RL4-1 closes latching RL4 energized via a normally closed external

contact connected between the 125 volt positive supply and multicore

3/2.

RL4-3 opens and, provided LK19 is omitted, the power factor

controller is switched out of operation for the period that RL4 remains

energized. Figure 7-2 shows the simplified arrangement.

Power factor control can be re-selected by disconnecting the d.c..

supply from multicore 3/2.

Figure.7-1 Simplified PFC Latch Circuity


98�

7.2.3 Link Identifications

LK1 &

LK4

Selects the ‘power factor’ mode of operation.

When fitted LK2 and 3 should be omitted.

LK2 &

LK3

Selects the ‘reactive current’ mode of operation. When

and 4 should be omitted.

LK5 &

LK7

Selects the remote ’level’ potentiometer. When fitted

LK6 and 8 should be omitted.

LK6 &LK8 Selects the internal ‘level’ potentiometer. When fitted

LK5 and 7 should be omitted.

LK9 Selects the output to pulse the motorized voltage setting

potentiometer.

7.3 COMISSIONING PROCEDURE

This selection describe the commissioning procedure for the power

factor control card and should be read in conjunction with the general

commissioning procedure, section 11, and any specific contract


IMPORTANT

1) Check the correct links are fitted as detailed ‘a setting record for

MAVR

testing with test generator’.

2) Complete commissioning of the control card prior to commissioning

the power factor card.

3) Check External Connections according to “0NQ.359.019 MAVR

Circuit diagram” and “0NQ.162.118 MAVR back panel scheme”

7.3.1 Open loop operational checks

1) Remove the power factor controls card from the rack and refit

together with the extension card. Remove LK9 and connect a d.c..

voltmeter (20 kohms per volt or more) on the 10V d.c.. range

between TP5 (-Ve) and TP1. Remove LK2 and LK3. Fit LK1and


99�

LK4.

2) Run the generator up to speed, synchronism with the system and set

the output power to approximately 20% of rated power. Set the

generator power factor to unity by adjustment of the motorized

voltage setting potentiometer if necessary.

3) Turn either the local or remote ‘level’ potentiometer, whichever is

applicable, fully clockwise and check that the voltmeter registers

between 6 and 8 volts positive.

4) Reverse the voltmeter connections and turn the level potentiometer

fully anti-clockwise. Check that the voltmeter registers between 6

and 8 volts positive.

7.3.2 Power Factor control mode of operation checks (if applicable)

1) Adjust the ‘level’ potentiometer to bring the voltmeter reading

down to zero –a slight drift is unavoidable duo to an integrating

action. Refit lK9.

2) Select power factor control operation if not already selected,

(shorting multicore 2 wires 1 and 5 together) by the appropriate

selector switch or breaker auxiliaries and note the ‘PFC On’ LED

on.

Manually adjust the motorized voltage setting potentiometer and

check the power factor is controlled to unity by the motorized

voltage setting potentiometer being pulsed back to its original

position. Any overshoot or slow response indicates the stabilizing

controls need optimizing as detailed below in sub-section 7.3.4.

3) It is normally to latch off the power factor control circuit following a

remote raise or lower signal to the motorized voltage setting

potentiometer, thereby reverting to manually power factor

adjustment. During the commissioning procedure this should be

avoided by disconnection of external wiring to multicore 3/2 and

multicore 1/9 & 1/12 until required in sub-section 7.3.5.


100�

4) Adjust the ‘level’ potentiometer to give the required power factor.

Vary the generator output power from 10% to full power and check

that the steady state power factor is kept constant. Note that if the

motorized voltage setting potentiometer reached an end stop, power

factor can no longer be maintained.

7.3.3 Reactive Current Control mode of operation checks (if applicable).

1) Adjust the 'level' potentiometer to bring the voltmeter reading

down to zero --a slight drift is unavoidable due to an integrating

action. Refit LK9, remove LK1 and LK4 .Fit LK2,LK3.

2) Select power factor control operation if not already selected,

(shorting multicore 2 wires 1 and 5 together) by the appropriate

selector switch or breaker auxiliaries and note the ‘PFC On’ LED on.

Manually adjust the motorized voltage setting potentiometer and

check the reactive current is controlled to zero by the motorized

voltage setting potentiometer being pulsed back to its original

position. Any overshoot or slow response indicates the stabilizing

controls need optimizing as detailed below in sub-section 7.3.4.

3) It is normal to latch off the power factor control circuit following a

remote raise or lower signal to the motorized voltage setting

potentiometer, thereby reverting to manually reactive current

adjustment. During the commissioning procedure this should be

avoided by disconnection of external wiring to multicore 3/2 and

multicore 1/9 & 1/12 until required in sub-section 7.3.5.

4) Adjust the ‘level’ potentiometer to give the required power factor.

Vary the generator output power from zero to full power and check

that the steady state power factor is kept constant. Note that if the

motorized voltage setting potentiometer reached an end stop then

the reactive current control can no longer be maintained.

7.3.4 Optimization of response

1) Two controls('Slug' and 'gain') are incorporated on the unit to allow


101�

response optimization. The 'slug' potentiometer slows the response

of the unit to system transients whilst the 'gain' potentiometer

adjusts the width of the output pulse for a given error. By

adjustment of these two controls the motorized voltage getting

potentiometer can be made to quickly close-in the final position by

continuous movement finally being 'inched' in with shorter duration

pulses thereby avoiding overshoot or excessive pulsing.

2) To check the response turn the motorized voltage setting

potentiometer approximately 1 quarter of a turn away from its

initial position and watch the response in returning to the final

position. The initial movement should be continuous until nearly

back to its final position when it should be pulsed, the length of

pulses getting shorter as the final position is reached. If the pulses

are too short turn the 'gain' potentiometer clockwise and vice versa.

If frequent correction pulse are being given once the initial error

has been overcome this could indicate too long a pulse or

insufficient slug, in this case first decrease the 'gain' and then

increase (turn clockwise) the 'slug'. If the overall response is very

slow decrease the 'slug' by turning the potentiometer anti-clockwise.

It is important that excessive pulsing is avoided as this will

inherently reduce the system reliability.

7.3.5 Power Factor Control Inhibit Latch(if applicable)

1) As already described this circuit is included to enable cancellation of

the power factor control circuit by operator intervention. The

circuit detects either an external raise or lower pulse given to the

motorized voltage setting potentiometer which latches a relay to

inhibit the power factor control card. Return to automatic operation

is achieved by breaking the external latching path. This circuit is

incorporated on the 'back panel '.

2) Reconnect the external wiring to multicore 3/2 and multicore 1/9


102�

and 1/12. Select power factor control operation and verify correct

operation. Give an external raise signal to the motorized voltage

setting potentiometer (i.e. auxiliary d.c. positive to multicore 1/9)

and check no corrective action is initiated by the power factor

control card until the latching circuit is broken by the appropriate

external logic (i.e. breaking the auxiliary D.C.. positive feed to

multicore 3/2). Repeat this procedure but with an external lower

signal to the motorized voltage setting potentiometer (i.e. auxiliary

d.c.. positive to multicore 1/12).

7.3.6 VAr shed operational check (if applicable)

1) With the generator in parallel with the system and power factor

control operation selected (either in power factor or reactive current

control mode) takes up 20% to 50% of rated load.

2) Select 'VAr shed' (shorting multicore 2/3 and 2/5 together) by the

appropriate selector switch or control logic and note that 'VAr shed'

LED comes on simulations with a reduction of generator output

VArs to zero, i.e. unity power factor.

3) Vary the generator output power from zero to full load and check

that the VArs are controlled to zero, or power factor to unity. Switch

off the VAr shed signal and check return to normal operation.

7.3.7 Remote Level control on twin systems (if applicable)

1) When the remote 'level' potentiometer is selected the internal 'level'

potentiometer is connected across it via series resistors. This feature

enables any mismatch between the two MAVR units 'level'

potentiometers to be compensated for. To minimize this error run the

generator in parallel with the system with power factor control

selected and local 'level' potentiometers set to 5.0 both MAVR's.

2) Set the remote 'level' potentiometer to the normal operating level

and note the controlled power factor or reactive current. Select the

other MAVR unit and check its quiescent controlled power factor or


103�

reactive current . If the latter controls to a more lagging level turn its

local 'level' potentiometer say 1.0 division clockwise, and if to a more

leading power factor in the opposite direction. Repeat the transfer

between MAVR units and again check the quiescent controlled levels,

minimizing any mismatch by adjusting the local 'level'

potentiometers as described.


This section describes the fault finding procedure for the power

factor control card and should be read in conjunction with the general

fault finding section 10.

IMPORTANT


connections -thoroughly check all connections are correct to the

0NQ.359.019 MAVR circuit diagram.


record for 6.

In general faults associated with the power factor control card can

be separated into two categories:

Non-operation (Table 7)

Mal-operation (Table7)

Table 7-4.1 Non-operation


1.Output not selected CheckLK9 is fitted Correct

2.External signal to

select operation not

given

Check external wiring

between 2/1 and 2/5

should be shorted for

PFC unit operation.

Correct as

necessary

3.Positive of auxiliary

D.C.. not connected to

card.

Check positive of

auxiliary D.C.. is

connected to 3/9.

Correct as

necessary.


104�

4. Card latched out of

operation by external

signal.

Break latching path to

3/2 and check RL4 is

de-energized.

Check external

logic and correct as

necessary.

5.Links selecting

mode of operation

(power factor or

reactive current) &/or

local remote

adjustment links

missing.

Check links fitted as

detailed in section 7.3.2

& 7.3.3

Correct as

necessary

6.insufficient output

pulse duration to

MVSR.

Check 'gain' control

setting

Correct as detailed

in 7.3.4

7.Loss of power

supply

Check FS1 & 2 and any

external fuses and

wiring to he auxiliary

supply.

Replace blown fuse

or correct as

necessary.

8.PF Control card

faulty.

Interchange card with a

spare

Replace card and

return to the Works

for repair.

9. Main frame failure Loss of sensing signals

(Sensing volts,2.5V a.c.

(21) to (29) & sensing

current,30V @5A,(11)

to (12), Loss of power

supplies.

See 3.

Table 7-4.2 Non-Operation

No. System Possible Fault Test Remedial

Action


105�

1. Control is to

unity power factor

only

a. VAR shed

selected

(VAR shed

LED is on)

b. Incorrect links

selected

c. External

wiring fault.

Check external

wiring between

2/3 &2/5

should be open

circuit

Check links

7.3.2 & 7.3.3

Check wiring

to 4/1,4/2,4/4

Correct as

necessary

Correct as

necessary

Correct as

necessary

2.Control is to

extend units range

a. C.T and /or

P.T sensing

phasing

incorrect

b. External

'level' pot.

Connections

incorrect

remote control

only

c. Incorrect links

selected.

Check to

MAVR circuit

diagram.

Check to

MAVR circuit

diagram.

See section

7.3.2 & 7.3.3

Correct as

necessary

Correct as

necessary

Correct as

necessary

3.Response very

slow or unstable

'Slug & gain'

control

incorrectly

crossed.

Check links

7.3.3 & 7.3.2

See section

7..3.4

Correct as

necessary

4. Unit has wrong

range of control.

Power factor

/reactive current

links crossed.

Check links

7.3.2 & 7.3.3

Correct as

necessary

5. 'Remote' or

'Local'

potentiometer

ineffective.

Local/Remote

links missing or

crossed.

Check links

7.2.2

Correct as

necessary


106�

6. 'Volts Set'

potentiometer

motored prior to

synchronous to

system

PF Control

operation

permanently

selected.

Check external

wiring between

2/1 & 2/5

should be open

circuit during

single running

Correct as

necessary

7. Manual

intervention does

not cause PF

Control lockout.

PF Control

latching path

open circuit

Check external

wiring between

3/2 & auxiliary

d.c. positive

should be short

circuit.

Correct as

necessary


107�


108�

8. EXCITATION MONITOR CARD TYPE A

8.1 SPECIFICATION

8.1.1 Over Excitation Monitor

1) Tripping Level

The tripping level is adjustable within the range 5 to 15A, or an

input voltage of between 0.8 and 2.5 volts in the case of a static

excitation scheme.

2) Increased Sensitivity Feature

An internal link enables the sensitivity to be increased by a

factor of 4(±2.5%) to allow setting up without overexciting the

generator.

3) Temperature Compensation Facility

Temperature compensation of the monitor tripping level can be

achieved from the ‘Excitation Limiter’ card, the level of

compensation being independently controllable. The specification

of this facility is identical to the ‘Excitation Limiter’, see section

3.5.1.3.

4) Time Delay

An adjustable ‘integrating delay’ is incorporated giving delays

from 1000%-seconds to 100%-seconds. This corresponds to a range

of 10 to 1 seconds for a 100% error, i.e. excitation twice the nominal

tripping level.


-25℃ to +65℃ : Operating

-40℃ to +100℃ : Storage

6) Accuracy

Tripping level ±2% repeatability provided the temperature is

within ±15℃


109�

Time delay ±5% repeatability of that at which the unit was

set, and with no temperature

compensation.

8.1.2 Under Excitation Monitor

1) Characteristic

(1) MVAr Limit at Zero Power, this is set by the ‘Xd’ control. When

the input voltage and current supplied to unit are nominally

110V and 5A the ‘Xd’ control gives an MVAr trip level ranging

from 12.5% to 100% of the rated MVAr. This is equivalent to a

generator reactance range from 0.8 to 1.0 p.u..

(2) Tripping Level Curvature, this is set by the ‘Xe’ control. When

the input voltage and current supplied to the unit are nominally

110V and 5A the ‘Xe’ control compensates for external reactance

effects (e.g. unit transformers) in the range 0 to 0.4 p.u.

2) Time Delay

An adjustable integrating time delay is incorporated in the unit

for use on monitors to avoid transients causing spurious operations.


-25℃ to +65℃ : Operating

-40℃ to +100℃ : Storage

4) Accuracy

Tripping level ±2% repeatability provided the

temperature is within ±15℃

Monitor Time delay ±5% repeatability of that at which the

unit was set.

5) Input Signals

It requires a 5A current transformer input of 1VA rating in the

yellow phase. The voltage sensing is derived from the red to blue

sensing signal.


110�

8.1.3 Common – Controls and Indications

Slug UE: A front access multi-turn potentiometer which adjusts the

under excitation monitor time delay.

OE Delay: A front mounted, single turn potentiometer with a calibrated

dial scaled 0 to 10 which adjusts the time delay of the over

excitation monitor.

Set Xd: A front mounted, single turn potentiometer with a calibrated

dial scaled 0 to 10 which adjusts the operating level of the

unit at zero power.

Set Xe: A front mounted, single turn potentiometer with a calibrated

dial scaled 0 to 10 which adjusts the curvature of the

monitor characteristic.

Set If: A front access multi-run potentiometer that adjusts the over

excitation monitor field current tripping level.

Set T.C.: An internal access multiturn potentiometer which adjusts

the temperature compensation range (i.e. effective

compensation achieved in %/℃.)

OE Trip: A front mounted ‘Light Emitting Diode’ to give indication of

operation of the over excitation monitor.

UE Trip: A front mounted ‘Light Emitting Diode’ to give indication of

operation of the under excitation monitor.

Relay Output : For remote indication of an over or under excitation

monitor trip Condition a common relay mounted in the

mainframe is energized.


(Number in brackets ( ) refer to printed circuit board edge connections).

8.2.1 Over Excitation Monitor

(This is shown on the lower half of the schematic diagram).


111�

On a brushless excitation system field current is sensed across the

back panel mounted stabilizing resistor R1, R2, and the signal is

supplied to the monitor at (29) and (2).

On a static excitation system the signal is derived from a D.C.

current transformer-measuring rotor current. On the units supplied

before 1981 the output of the C.T. feeds the MAVR at multicore

terminals 1/10 and 1/7 and is routed to monitor (2) (29) via LK16 and

LK7 on the backpanel. On the type A mainframe the C.T. supplies

MAVR terminal 1/14 and 1/10, LK8 being fitted on the backpanel.

A current proportional to the field current is compared to the

stabilized reference current lowing through R56. When the field current

exceeds a preset level determined by the reference current and the

setting of RV5 the output voltage of IC3b begins to fall, causing IC3c to

rise and turning on VT3 and VT4 producing local indication of monitor

operation by LED2, and energizing the common monitor relay, (RL2 on

the back panel) via D23 and (9).

D21 and R67 provide positive feedback that latches VT3 and 4 on,

once the monitor has operated. The output can be reset by removing the

D.C. supply from (24) by depressing the ‘monitor reset’ pushbutton,

which is fitted to the fixed front panel on a MAVR incorporating fault

monitors.

When LK7 is fitted, the sensitivity is increased by a factor of four,

which facilities commissioning of the monitor at reduced levels of

excitation.

RV6 and C10 provide an adjustable integrating time delay, before

the monitor operates.

The temperature compensation signal is derived from the excitation

limiter via (25), potentiometer RV3 providing adjustment of the level of

compensation fed to IC3b via R55 and LK4. LK4 inhibits this signal

when removed.


112�

8.2.2 Under Excitation Monitor

(This is shown on the upper half of the schematic diagram).

The under excitation limit of a generator operating in parallel with

a system is determined by the generator and system reactance, and can

be represented on a generator operating chart.

If the excitation is reduced to a level that would cause the generator

to operate at a power factor more leading than is shown on the chart,

the angle by which the internal emf of the generator leads the system

voltage will extend 90 and loss of synchronism may occur.

Figure 8-1 shows a typical operating chart and the effect of

differing external reactance between the generator and the infinite

system. Such a reactance could be due to transformers.

Figure 8-1 Generator Operating chart

So that the operation of the monitor can be understood it is

necessary to be aware of the relationship between the simplified vector

diagram of the generator and the generator-operating chart.

Figure 8-2 below shows the equivalent circuit and vector diagram of the

generator paralleled to an infinite system.

I = generator current

Et = generator internal emf

Vt = generator terminal voltage


113�

V = system voltage

Xd = generator synchronous reactance

Xe = external reactance

Figure 8—2

Figure 8—3 shows how the vector diagram can be related to the

generator-

operating chart.

The condition is drawn for line current I, at φ leading. The under

excited limit occurs when the internal Emf, Et, leads the voltage of the

infinite system by 90 degree.

It can be seen that when Xe=0, the limit is a straight line

corresponding to constant leading MVAr’s of 1/Xd per unit, and that as

Xe increases the MVAr limit reduce with increasing power.

Figure 8—3

IXe Xd Et V


114�

8.2.3 Operation

(All voltage levels are relative to TP1).



nominally 28mA supplied by T5 on the back panel. Whose center tap

also feeds (21). The phasing of these signals is such that the current lags

the voltage by 90 degree, when generating at unity power factor.

The input circuit comprising R1, R5, R9, RV1, RV2, is arranged so

that voltages corresponding in phase and amplitude to the internal emf

of the generator, and the system voltage, are produced at TP3 and TP4

respectively. IC1a, IC1b, IC1c, and IC2 form a circuit that produces a

mean positive voltage across C3 when the voltage at TP3 leads that at

TP4 by less than 90 degree; and a mean voltage when the voltage at TP3

leads that at TP4 by more than 90 degree. The latter case corresponds

to an under excited condition, current through R19 causing the output

of IC1d to rise, turning on VT1 and VT2 and producing a local

indication of monitor operation by LED1, and energizing the common

monitor relay, RL1 on the back panel, via D14 and (9). D12 and R26

provide positive feedback that latches VT1 and 2 on, once the monitor

has operated. The output can be reset by removing the D.C. supply

from (24) by depressing the ‘monitor reset’ pushbutton that is fitted on

the fixed front panel of a MAVR incorporating fault monitors.

The output of the monitor can be inhabited by linking multicore 2/5

and 3/7 which ensure that the output of IC1d remaining negative due to

a feed through R71 and D25. This facility can be used to inhibit the

monitor under certain single running condition to increase the overall

reliability.

RV4 and C6 provide an adjustable delay that should be set to

prevent the relay tripping due to transient swings in load angle.


115�

8.2.4 Link Identification

Link LK1 Selects the under excitation relay output. When fitted

LK1A must be omitted.

Link LK1A Inhibits the under excitation relay output. When fitted

LK1 must be omitted.

Link LK2 Selects the over excitation relay output. When fitted

LK2A must be omitted.

Link LK2A Inhibits the over excitation relay output. When fitted

LK2 must be omitted.

Link LK3 Selects monitor override on under excitation monitor.

Link LK4 Selects temperature compensation.

Link LK7 Selects an increase of sensitivity by a factor of 4 on the

over excitation monitors for commissioning purposes

only. When fitted LK8 must be omitted.

Link LK8 Selects the normal operating sensitivity of the over

excitation monitor. When fitted LK7 must be omitted.



excitation monitor card and should be read in conjunction with the

general commissioning procedure, Section D, and any specific contract


IMPORTANT

(1) The potentiometers 'OE Delay', 'Set If’, 'Set Xd', 'Set Xe', and 'Set

TC' have been set to correct level at the factory and should not

require site adjustment.

(2) Check that the correct links are fitted as detailed in the test record--

'MAVR Tests with Test Generator' subsection 6, or by reference to

sub-section 8.2 of the handbook.


116�


the excitation monitor card. Temporarily remove the excitation

limiter card during commissioning of the monitor card except when

checking temperature compensation. If applicable, inhibit the

monitor relay from causing transfer to an alternative excitation

source.

8.3.1 Over Excitation Monitor x4 level

(1) Determine the limited parameters. (Over excitation limit x1 and

x4, differential, delay and temperature compensation) from test

record--'MAVR Tests with Test Generator' section. In the

absence of these, typical setting are: the x1 limit 10% higher

than the continuous full load rating of the exciter or main field

of the generator, the differential to 100% (Link 11), the time

delay to 400% seconds, and the temperature compensation to

80% of the 0℃ level for a temperature rise of 40℃.

(2) Remove the monitor card and re-insert together with the

extension card, the latter is behind one of the MAVR blank

front panels. Connect a 10-volt D.C. voltmeter (20 Kohm per

volt or more) across TP6 (+ve) and TP1. Remove LK4 if fitted.

(3) Select the x4 increased sensitivity feature by removing link LK8

and fitting LK7, thereby enabling the approximate operating

level of the monitor to be checked at a low excitation level.

Insert a suitable ammeter in the field circuit if one is not

already available.

(4) Run the generator up to rated speed, single running and on no


117�

load with "auto' excitation selected.

(5) Check that no external monitor operation signal is given (i.e. an

open circuit between multicore 2 wires 4 and 6, and the 'OE

Trip' LED is off). This assumes that the no-load excitation is

less than 25% of the preset over excitation trip level. In the

event of it having tripped reset the circuit by the reset

pushbutton on the left hand side of the mainframe.

(6) ncreases the excitation to above the preset over excitation trip

level divided by 4 (to allow for the x4 increase in sensitivity) by

adjusting the motorized voltage setting potentiometer and if

necessary the ‘set V’ potentiometer on the control card. Note

that the voltmeter reading slowly reduce indicating correct

operation, adjust the excitation as necessary to maintain the

voltmeter reading at zero – a slow drift is unavoidable due to

the integrating acting. The excitation current is then at the x4

trip level.

(7) If this level is incorrect by more than ±2.5% then the ‘Set If’

potentiometer has been reset since the unit left the factory and

requires readjustment. To increase the over excitation trip level

rotate the ‘Set If’ potentiometer clockwise and vice versa. In the

event of a trip signal being given reduce excitation and reset the

unit by the reset pushbutton.

(8) Increase the excitation above the x4 trip level and check that

monitor operating is given, (i.e. a short circuit between

multicore 2 wires 4 and 6, and the ‘OE Trip’ LED on). Reduce

the excitation to below the x4 trip level and check that monitor

operation is still indicated until the reset pushbutton is

depressed.

(9) The over excitation monitor is now set to trip at approximately

the required level when the x1 sensitivity is reselected by


118�

removing link LK7 and fitting link LK8. Readjust the

motorized voltage setting potentiometer to mid-range and

adjust the control card ‘Set V’ potentiometer to give nominal

line voltage.

1) Over excitation Monitor. Check on Temperature Compensation

Facility x4 Sensitivity

When the temperature compensation facility provided on the

over excitation limiter is utilized, the operating level of the over

excitation monitor is also compensated according to temperature.

The compensation circuit fitted to the limiter card feeds into the

monitor card (pin 25).

(1) Perform tests 8.3.1.5 to 8.3.1.9 above.

(2) Confirm that the over excitation limiter has been commissioned

according to section 6-3 parts A and AA.

(3) Determine the dc voltmeter reading obtained in test 6—3 and

check that the voltage measured across TP10 (+ve) and TP1

corresponds to the ambient temperature at the location of the

RTD.

The voltmeter should indicate

Ambient Temperature (℃) X

Voltmeter reading in test C5-3 AA.V

40

(Test not applicable at ambient temperature below zero).

Adjust RV3 to provide required reading if necessary.

3) Refit link LK4.

8.3.2 Over Excitation Monitor - x1 level

1) Synchronize the generator to the system and lightly load the

generator (5 - 10% of rated power).

2) Gradually increase the excitation by clockwise adjustment of the

motorized voltage setting potentiometer to an excitation level just in


119�

excess of the recommended x1 trip level. The voltmeter should

display a slowly falling reading indication correct operation. Adjust

the excitation as necessary to maintain the voltmeter reading at zero

- a slow drift is unavoidable due to the integrating action. The

excitation current is then at the x1 trip level. If difficulty is

encountered in reaching the required excitation rotate the control

card ‘Q.C.C’ potentiometer anti-clockwise.

3) If necessary trim the 'Set If' control to give the required excitation

level with a zero reading on the voltmeter. Clockwise rotation

increases the trip level and vice versa.

8.3.3 Over Excitation Monitor – Temperature Compensation (If applicable)

1) Remove LK12 and fit LK12A on the excitation limiter card, together

with the following:

100 ohm RTD Fit LK15 & 17 Omit Links 1, 2, 13, 14, 15,

18

130ohm RTD Fit LK13 & 17 Omit Links 1,2,14,15,16,18

Leave all other links as fitted and replace the limiter card.

2) Synchronize and lightly load the generator, increase the excitation

and check that the monitor operates as in section 8.3.3. Check that

the trip level is within 1% of the required 0℃ Over Excitation

Monitor level.

3) Reduce the excitation to nominal, reset the monitor and reselect the

links on the limiter card as follows:

100 ohm RTD R Remove LK15 Fit LK16

130 ohm RTD Remove LK13 Fit LK14

4) Increase the excitation and check that the monitor now trips at a

lower level corresponding to 40℃ over excitation monitor trip level

±2%. If necessary adjust RV3 (set T.C.) on the monitor card to

achieve this. If no figure is available for this limit assume a value of


120�

0.8x the 0℃ monitor level. Clockwise rotation of RV3 increases the

amount of temperature compensation i.e. reduce the 40℃ monitor

level and vice versa.

5) Reduce the excitation to nominal, reset the monitor and reselect

links on the limiter card as follow:

100 ohm RTD Remove LKs 16 & 17 and fit LKs 1& 18

130 ohm RTD Remove LKs 14 & 17 and fit LKs 2 & 18

The external RTD is then selected.

6) Increase the excitation and check the monitor operates at a new

level dependant upon the external RTD temperature, ‘t’. Knowing

this temperature check that the trip level, ‘I’ is

Where I0 = 0℃ limit

I40 = 40℃ limit

If incorrect check that the nominal RTD resistance and connections

are correct.

Refit LK12 and remove LK12A on the Limiter card and leave this

card out.

8.3.4 Over Excitation monitor –Time Delay

1) Whilst still in parallel with the system short out TP8 to TP1 with a

temporary link. This shorts out the over excitation monitor sensing

output so that the monitor reset – indicated by the voltmeter

resetting to above 9 volts.

2) Set the excitation to ‘X%’ above the over excitation trip level

(preferable 10% or more – but at least 5%). Reset the monitor if

necessary. Time the period taken, ‘t seconds’, between removing the

short between TP8 and TP1 and the monitor giving trip indication.

2%

40

t*I40-I0*I0 I


121�

The produce ‘X’ x ‘t’, give the over excitation monitor time delay

expressed in %-SEC’s.

3) If necessary, turn the ‘OE Delay’ control to give the required

%-SEC’s delay; clockwise rotation increasing the delay and vice

versa. When rechecking the time delay allow the monitor to fully

reset, i.e. the voltmeter reading above 9 volts, and cancel the trip

signal by the reset pushbutton.

4) Reset the Q.C.C potentiometer to the required setting if it was

adjusted. Reduce excitation by turning the motorized voltage setting

potentiometer anti-clockwise to give unity power factor. Remove the

voltmeter between TP6 and TP1.

8.3.5 Under Excitation Monitor –Zero Power Level

1) Determine the under excitation monitor parameter (‘Xd’ and ‘Xe’

levels) from the test record- ‘MAVR Tests with Test Generator’

subsection 5. In the absence of these reference should be made to the

generator operation chart, the ‘Xd’ control should be set to the

machine loading capability at zero power and the ‘Xe’ control to any

quoted external reactance figure or a safe level – say 0.1 p.u.

Reactance. ’Xe’ can also be measured by synchronizing the

generator to the system and adjusting the power to zero: by noting

the per unit change in reactive load(ΔQ) for a given change in

system voltage (ΔV p.u.) of say 0.05 p.u. caused by changing the

motorized voltage setting potentiometer, Xe:

To simulate an exact under excitation tripping characteristic

reference should be made to

Fig.8-4. below. A circle gives the tripping level.

p.u. Xd

1

Xe

1

2

1radius

p.u. Q

V Xe


122�

Thus knowing the required circular characteristics centre and radius

the two parameter

‘Xd’ and ‘Xe’ can be deduced.

Fig 8-4 Under Excitation Monitor Characteristic

2) Connect a 10-volt D.C. voltmeter (20 kohm per volt or more). Across

TP5 and TP1 (+ve). With the machine running in parallel with the

system on ‘auto’ excitation, set the generator output power to zero.

Reduce the excitation by slowing rotating the motorized voltage

setting potentiometer anti-clockwise and check that the monitor

operates when the trip level is exceeded. Operation is indicated by

the ‘UE trip’ LED coming on and a short circuit between multi-core

2 wires 4 and 6. Increase the excitation to below the limit and check

that indication is given until the test pushbutton is operated. Reduce

the excitation again and set to a level that corresponds to a zero

reading on the voltmeter – a slow drift being unavoidable due to the

integrating action. The excitation is then set to the tripping level,

check that this corresponds to the required level and adjust the

p.u. Xd

1 -

Xe

1

2

1centre


123�

tripping level, if necessary, by adjustment of the ‘Xd’ potentiometer,

clockwise rotating decreasing the level and vice versa.

8.3.6 Under Excitation Monitor – ‘Xe’ Control

1) Increase the excitation to give unity power factor by clockwise

rotation of the motorized voltage setting potentiometer. Remove the

excitation monitor card from the rack.

2) Knowing the required external reactance, Xe, calculate from the

following the required resistance of the ‘Xe’ potentiometer:

(This figure is given in ‘MAVR Tests with Test Generator’ Section

QC48, subsection 7, page1).

Check using a digital ohm-meter that the resistance between TP2 and

TP4 agrees with that calculated. If it is incorrect adjust the ‘Xe’ control,

clockwise rotation will increase the resistance and vice versa. If a digital

ohm-meter is not available the ‘Xe’ control setting can be checked as

detailed in subsection 8.3.8 (Below). Replace the excitation monitor card.

8.3.7 Under Excitation Monitor – Tripping Level Characteristic

1) To check the tripping level characteristic throughout the range

adjust the excitation to give a zero reading on the voltmeter at

various generator output power from zero to maximum. By

checking the reactive power at these levels a comparison can be

made with the generator operating chart when it shows the under

excitation monitor tripping level.

2) If the operating chart is not available or shows insufficient

information, or ‘Xe’ could not be checked as detailed in subsection

F the following procedure should be adopted. Knowing ‘Xd’ and

ohms

current) C.T. p.u.sensin (1

Xe.p.u.*5*60R

5) (nominally ratio C.T. Sensing

current line ratedcurrent) C.T. sensing p.u. (1 Where


124�

‘Xe’ per unit values, calculate the radius and centre of the tripping

level circular characteristic as shown in Figure 8-4. Referring to

figure 8-4, for any generator output power, ‘OX’, the corresponding

tripping level of reactive power, ‘XY’, can be calculated as follows:

3) From the above calculations the theoretical and practical tripping

level curves can be compared and any errors compensated for by

appropriate adjustment of the ‘Xd’ and ‘Xe’ potentiometers. In

general the ‘Xd’ control sets the zero power trip level and the 'Xe'

control the curvature of the characteristic.

NOTE: The generator-operating chart is normally drawn for

operation at nominal voltage, although the actual limiting

curve of the generator and system reduces in proportion to

the square of line voltage, and the limiter incorporates this

characteristic.

If the limiter characteristic is being checked the reading of

MVAr should be divided by (per unit volts) squared, at line

voltages other than nominal.

8.3.8 Under Excitation Monitor – Time Delay

1) Remove the voltmeter and extender card. Replace the excitation

limiter card in the rack and adjust the excitation to unity power

factor.

2) At various generator output power from zero maximum check that

a sudden reduction in excitation caused by quickly rotating the

motorized voltage setting potentiometer fully anti-clockwise cause

the excitation limiter to operate before the under-excitation monitor

trips. If the monitor operates first rotate the ‘Slug UE’

potentiometer clockwise until the above condition can be set.

3) Reconnect the excitation monitor output relay to revert to the

OA centreOXpower p.u.AC reactivep.u. XY''power Reactive 22


125�

normal operational scheme.


This section describes the fault-finding procedure for the Excitation

Monitor card and should be read in conjunction with the general fault

finding section E.

IMPORTANT

(1) The majority of excitation fault are caused by incorrect connections-

thoroughly check all connections are correct to the contract

schematic diagram.

(2) Check that the correct links are fitted as detailed in the test record –

‘MAVR Test With Test Generator’ subsection, or by reference to

subsection 8-2 of the handbook.

In general faults associated with the Excitation Monitor Card can

be separated into two categories (Over and Under Excitation Monitor) viz:

Over Excitation Monitor – Inoperative (Table 8.4.1)


- Operator faults (Table 8.4.3)

Under Excitation Monitor- Inoperative (Table 8.4.4)


- Operator faults (Table 8.4.6)


NOTE: If any card is returned to the Works for repair please quote the

Type/Model/Contract numbers which appear inside the MAVR

front door, and on the right hand side of the mainframe

together with the nature of the fault.

Table 8.4.3 Over Excitation Monitor – Operational Faults

No

.

System Possible

Fault

Test Remedial

Action


126�

1. Monitor

operates when

machine on

load.

Set If control

set too low.

Check level as

in Section

8.3.2

Reset level, if

necessary as

in Section

8.3.2

2. Monitor

operates due to

transient on

load

applications.

‘OE Delay’

set too short.

Check delay as

in Section

8.3.4

Reset delay, if

necessary as

in Section

8.3.4

3. On a twin

system the

monitor causes

transfer before

limiter

operates.

Relative

levels and

time delays

of limiter

and monitor

incorrect.

Check levels &

delays as

detailed in 6.3

and 8.3

Reset as

necessary as

in Section 6.3

and 8.3.

4. Local

indication

given but relay

output

inoperative.

Mainframe

failure.

Monitor relay

faulty (RL2 on

Mainframe).

Replace relay

RL2.

5. Monitor

operates but

does not give

latched

indication.

Monitor

failure.

Interchange

monitor card

with a spare.

Replace

monitor card

and return to

Works for

repair.

6. Monitor low at

high

temperatures.

Excessive

temperature

compensatio

n.

Check as

detailed in

Section 8.3.3.

Correct as

necessary.


127�

Table 8.4.4 Under Excitation Monitor – Inoperative

No

.

Possible fault Test Remedial Action

1. Incorrect

output link

selected.

Check link LK2 is fitted

and LK2A omitted.

Correct as

necessary.

2. Loss of Power

Supply.


external fuses and wiring

to auxiliary supply.

Replace blown

fuse or correct as

necessary.

3. Mainframe

failure.

Loss of sensing signals

(Sensing volts, 2.5v, (21) to

(29) & sensing current,

22.5V at 5A (19) to (20)).

See Section 8.4

4. ‘Xd’ & ‘Xe’

controls set too

low.

Check level as in 8.3.5&

8.3.6.

Reset levels, if

necessary, as in

Section 8.3.5 &

8.3.6.

5. Monitor Card

Faulty.

Interchange Monitor card

with a spare.

Replace Monitor

card and return

to the Works for

repair.

Table 8.4.1 Over Excitation Monitor – Inoperative

No

.

Possible fault Test Remedial Action

1. Incorrect

output link

selected

Check link LK1 if fitted

and LK1A omitted.

Correct as

necessary.

2. Loss of power

supplies.

Check FS1& 2 and any


to auxiliary supply.

Replace blown

fuse or correct as

necessary.


128�

3. RTD short

circuit or an

associated

wiring fault or

limiter card

faulty.

Remove LK1 or 2 on

limiter card & check

correct operation. Check

RTD and wiring. Check

limiter card temperature

compensation.

Correct as

necessary.

4. Mainframe

failure.

No field current pick up

signal to monitor card (2)

& (29) – should be 150mV

to 1V on no load – or

internal power supply

failure.

See Section C1-4.

5. ‘Set If’ control

set too high.

Check level as in section

8.3.2.

Reset level, if

necessary, as in

section 8.3.2.

6. Limiter card

faulty.

Interchange monitor card

with a spare.

Replace monitor

card and return

to the Works for

repair.

Table 8.4.2 Over Excitation Monitor – Continuous Operation

No

.

Possible Fault Test Remedial Action

1. Increased

sensitivity link

selected.

Check link LK8 is fitted

and LK7 omitted.

Correct as

necessary.

2. ‘Set If’ control

set too low.

Check level as in Section

8.3.2.

Reset level, if

necessary, as in

section 8.3.2.


129�

3. RTD open

circuit, on

associated

wiring fault or

limiter card

faulty.

Remove LK4 & check

correct operation. Check

RTD wiring & Limiter

card temperature

compensation.

Correct as

necessary.

4. Control

card/sensing

failure giving

rise to an over

excited

condition.

See Section 4.4. See Section 4.4

5. Mainframe

failure.

Field current pick up

excessive (should be

nominally 0.17V between

(2) and (29) per amp of

excitation.

See section 3.4.

6. Monitor card

faulty.

Interchange monitor card

with a spare.

Replace monitor

card and return

to the Works for

repair.

7. Temperature

Compensation

Unit faulty.

Disconnect & check

monitor on its own.

Replace TCU &

return to Works

for repair.

Table 8.4.5 Under Excitation Monitor – Continuous Operation

No

.

Possible Test Remedial

1. C.T. and /or

P.T. sensing

phasing

incorrect.

Check to contract scheme. Correct as

necessary.


130�

2. Control card

failure giving

rise to an

under excited

condition.

See Section 4.4. See Section 4.4

3. Monitor Card

faulty.

Interchange Monitor card

with a spare.

Replace Monitor

card and return

to the Works for

repair.

4. Mainframe

failure.

All other tests fail to clear

fault.

See Section 3.4

Table 8.4.6 Under Excitation Monitor – Operational Faults

No

.

System Possible Fault Test Remedial

Action

1. Generator

loses stability

before limiter

operation.

Monitor level

set to low I.e.

outside

generator

capability.

Check

operating level

as detailed in

8.3.4 & 8.3.5.

Reset levels,

if necessary,

as in Section

8.3.5 &

8.3.6.

2. On a twin

system the

monitor causes

transfer before

limiter

operates.

Relatives level

and time

delay/stabilizi

ng of limiter

and monitor

incorrect.

Check levels

and

delay/stabilizin

g as detailed in

6.3 and 8.3.

Reset as

necessary as

in Sections

6.3 and 8.3.

3. Local

indication

given but relay

output

inoperative.

Mainframe

failure.

Monitor relays

faulty (RL2 on

mainframe).

Replace

relay RL2.


131�

4. Monitor

operates due to

transient

voltage

changes.

‘Slug UE’ set

too short.

Check slug as

in section 8.3.8.

Increase

‘Slug UE’ as

in section

8.3.8.


132�


133�

9 VOLTAGE MONITOR CARD

9.1 SPECIFICATION.

9.1.1 UNDER VOLTAGE MONITOR SPECIFICATIONS.

1) OPERATING LEVEL

The operating level is adjustable between 70% and 100% of

nominal voltage (110V).

2) Time delay.

An adjustable integrating time delay is incorporated having a range

of 2.5% --second to 25%--second (i.e. 100% error gives 25 ms to

250 ms delay).

9.1.2 OVER VOLTAGE MONITOR SPECIFICATIONS.

1) OPERATING LEVEL

The operating level is adjustable between 100% and 130% of

nominal voltage (110V).

2) TIME DELAY

An adjustable integrating time delay is incorporated having a

range of 10% --second to 100%--second (i.e. 100% error gives 100

ms to 1 second delay).

9.1.3 COMMON SPECIFICATIONS

1) ACCURACY

The operating level is maintained within ±1% of the selected

operating level subject to the following conditions:

(1) The temperature is within ±15℃ of the initial value.

(2) The frequency is within ±20% of nominal.

2) Input signals.

The unit requires a single phase, 110 volt nominal supply of

1VA rating at 50/60 Hz, separate to the control card sensing.


134�

3) Ambient Temperature Range.

Operating: -25℃ to +65℃.

Storage: -40℃ to +100℃

9.1.4 CONTROLS AND INDICATIONS.

1) Set OV: A front access multi-turn potentiometer which adjusts the

over voltage trip level.

2) Set UV: A front access multi-turn potentiometer which adjusts the

under voltage trip level.

3) OV delay: A front mounted single turn potentiometer with a

calibrated dial scaled 0 to 10 which adjusts the over voltage time

delay.

4) UN delay: A front mounted single turn potentiometer with a

calibrated dial scaled 0 to 10 which adjusts the under voltage time

delay.

5) OV trip: A front mounted ‘Light Emitting Diode’ to give

indication that the over voltage monitor has tripped.

6) UV trip: A front mounted ‘Light Emitting Diode’ to give

indication that the under voltage monitor has tripped.



connections, and all voltage level are relative to TP1.)

Sensing voltage supplied to multi-cores 2/7 and 2/9 is supplied to

(20) (22) via sensing fuses FS3, 4.

The sensing signal is isolated and rectified to produce a d.c. voltage

at TP7 that is used for both under and over voltage monitors.

9.2.1 Under Voltage monitor.

The input signal produces a current in R11 that compared with an

adjustable stabilized reference current flowing through R14. When the

input signal exceeds the reference, the output of IC1 (TP3) is negative,


135�

and VT3, 4 are non-conducting and no output signal is given. When the

input signal is less than the reference signal, the output of IC1 rises at a

rate determined by the error, and setting of RV2, and when TP3

becomes approximately 0.5 volt positive, VT3 and VT4 turn on

energizing the monitor relay R12 on the back panel via (8) and LED1

which provides local indication. Positive feedback via D5 and R22 keep

VT3 and VT4 on, even if the sensing voltage rises causing the voltage at

TP3 to fall.

The monitor relay R12 remains energized until the reset monitors

pushbutton (on the fixed front panel) is pressed which removes the +15

volt supply from (24).

The under voltage monitor can inhibited by a positive signal at (28)

which turns on VT1, VT2 producing a current through R12 which

over-rides the error signal, preventing the output of IC1 becoming

positive. This facility is used during operation of the falling frequency

protection and soft start facility where the line voltage is intentionally

controlled to a lower level.

9.2.2 Over Voltage Monitor

The input signal produces a current through R18 that is compared

with an adjustable stabilized reference current flowing through R26.

When the input signal exceeds the reference, the output voltage of IC2

(TP4) begins to rise at a rate determined by the error and setting of

RV4, and when TP4 becomes approximately 0.5 volt positive VT5, VT6

are turned on and the monitor relay R12 on the back panel is energized

via (8) and LED2 which provides local indication.

Positive feedback via R32 and D10 latch in the relay driver circuit

which cad be reset by operating the reset monitors pushbutton which

removes the +15 volt supply from (24).


136�

Inhibit monitors

Over and under Voltage monitors can be inhibited by applying +15

volts d.c. to (2), ensures that the output of both amplifiers remains

negative. This can be achieved by linking multi-cores 3/11 and 2/5 and is

sometimes used to increase the overall reliability of the fault monitor

when operating in parallel with a large system.

Link Identification

Link LK1 Selects the under voltage monitor output.

Link LK2 Selects the over voltage monitor output.

Link LK3 Selects the under voltage override input.

9.3 COMMISSIONING PROCEDURE.

This section describes the commissioning procedure for the voltage

monitor card and should be read in conjunction with the general

commissioning procedure, section D and any specific contract


IMPORTANT

(1) Check the correct links are fitted as detailed in the setting records

for MAVR tested with Generator sub-section 6.

(2) All potentiometers on the unit have been set to the correct level at

the factory and should not require any on-site adjustment.


the voltage monitor.

9.3.1 Over Voltage Monitor – Operating Level

1) Determine the over voltage parameters (level and time-delay) from

the test record ‘MAVR Tests with Test Generator’ section QC48,

sub-section 6, page 1. In the absence of these, typical settings are the

over voltage level 15% above the nominal line voltage and a time

delay of 20%-seconds although certain site operating conditions


137�

might require different settings.

2) Remove the voltage monitor card and re-insert together with the

extension card. Connect a voltmeter (20K ohms per volt or more)

on the 10V d.c. range between TP1 (+ve) and TP4. Inhibit any

transfer of excitation to a standby source due to monitor operation,

if applicable.

3) Run the generator up to speed and select ‘Auto’ excitation. Set the

motorized voltage setting potentiometer fully clockwise and adjust

the ‘set V’ control on the control card to give a line voltage of 105%

(in preparation for setting the time delay) of the over voltage trip

level.

4) Reduce the generator line voltage by turning the motorized voltage

setting potentiometer fully anti-clockwise and reset the voltage

monitor, if necessary, depressing the reset pushbutton on the left of

the mainframe.

5) Adjust the motorized voltage setting potentiometer until the

voltmeter indicates a slowly falling voltage, finally adjusting to give

a reading of zero on the voltmeter – a slow drift being unavoidable

due to an integrating action. The line voltage is then at the set level

of the over voltage monitor.

6) Due to sensing VT differences or adjustment of the set ‘OV’

potentiometer it may be necessary to reset the level. To increase the

level turn the ‘set OV’ potentiometer clockwise and vice versa.

Repeat the above procedure (AV) until the set level is correct.

7) Increase the voltage above the set level and check that the over

voltage monitor operates (i.e. a short circuit between multi-core 2

wires 4 and 6, and the ‘OV Trip’ LED on). Reduce the voltage below

the set level and check that monitor operation is still indicated until

the reset pushbutton is momentarily depressed.


138�

9.3.2 Over Voltage Monitor –Time Delay.

1) With the voltage below the set level and the monitor reset suddenly

turn the motorized voltage setting potentiometer fully clockwise and

measure the delay ‘t sec's’ (Using a stopwatch) before the ‘OV Trip’

LED is turned on.

2) The time delay is given by the product, 5 x ‘t’%-sec's (the error

being set to 5% in sub-section AIII). This time-delay should

correspond to that quoted in the test record.

3) If the time delay is incorrect then the ‘OV Delay’ potentiometer has

been reset since the unit left the factory and requires readjustment.

To increase the delay turns the ‘OV Delay’ potentiometer clockwise

and vice versa. Repeat the above procedure (BI & II) until the time

delay is correct.

9.3.3 Under Voltage monitor – operating level.

1) Determine the under voltage parameters (level and time delay)

from the test record – ‘MAVR Tests with Test generator’ section

QC48, sub-section 6, page 1. In the absence of these, typical settings

are the under voltage level 15% below the nominal line. Voltage and

a time delay of 10%-secs. , Although certain site operating

conditions might require different settings.

2) Set the motorized voltage setting potentiometer fully anti-clockwise

and adjust the ‘set V’ control on the control card to give a line

voltage of 97.5% of the under voltage trip level (in preparation for

setting the time delay). Connect a voltmeter (20 Kohms per volt or

more) on the 10V d.c. range between TP1 (+ve) and TP4 and

remove link LK3.

3) Increase the generator line voltage by turning motorized voltage

setting potentiometer fully clockwise and reset the voltage monitor,

if necessary by depressing the re-set pushbutton on the left of the

mainframe.


139�

4) Adjust the motorized voltage setting potentiometer until the

voltmeter indicates a slowly falling voltage, finally adjusting to give

a reading of zero on the voltage – a slow drift being unavoidable

due to an integrating action. The line voltage is then at the set level

of the under voltage monitor.

5) If this level is incorrect then the ‘set UV’ potentiometer has been

reset since the unit left the factory and requires read just-ment. To

increase the level turn the ‘set UV’ potentiometer clockwise and vice

versa. Repeat the above procedure (CIV) until the set level is

correct.

6) Decrease the voltage below the set level and check that the under

voltage monitor operates (i.e. a short circuit between multi-core 2

wires 4 & 6, and the ‘UV Trip’ LED on). Increase the voltage above

the set level and check that monitor operation is still indicated until

the reset pushbutton is momentarily depressed.

9.3.4 Under Voltage monitor – time delay.

1) With the voltage above the set level and the monitor reset suddenly

turn the motorized voltage setting potentiometer fully clockwise

and measure the delay, ‘t sec’s’, (using a stopwatch) before the ‘UV

Trip’ LED is turned on.

2) The time delay is given by the product, 2.5 x ‘t’%-sec’s (the error

being set to 2.5% in sub-section CII). This delay should correspond

to that quoted in the test record.

3) If the delay is incorrect then the ‘UV Delay’ potentiometer has been

reset since the unit left the factory and requires adjustment. To

increase the delay turn the ‘UV delay’ potentiometer clockwise and

vice versa. Repeat the above procedure (DI & II) until the time

delay is correct.

9.3.5 Under Voltage monitor –Override.

1) refit link LK3, set the line voltage to just above the under voltage


140�

trip level (the voltmeter indicating a slowly rising voltage) and

switch off the excitation.

2) Switch on the excitation after 2 minutes, the control card ‘soft start’

circuit having then reset, and check that the under voltage monitor

does not operate during build-up.

3) Reduce the generator speed to zero and check that the under voltage

monitor does not operate whilst on the frequency fall off

characteristic.

9.3.6 Voltage Monitor Inhibit Circuit (if applicable).

1) With the set running at rated speed on ‘Auto’ excitation inhibit the

voltage monitor by the appropriate external logic (shorting

multi-core 3 wire 11 to multi-core 2 wire 5).

2) Adjust the voltage above the over voltage trip level and below the

under voltage trip level and check that neither gives a trip signal.

9.3.7 Final Notes.

1) Reset the motorized voltage setting potentiometer to mid range and

adjust the control card ‘set V’ potentiometer to give the required

nominal line voltage.

2) Reconnect any logic that was disconnected to inhibit transfer of

excitation on monitor operation.

3) Remove the voltmeter and extender card and refit the voltage

monitor card.

9.4 FAULT FINDING PROCEDURE.

This section describes the fault finding procedure for the voltage

monitor card and should be read in conjunction with the general fault

finding section 9.4.5.

IMPORTANT.

(1) The majority of excitation faults are caused by incorrect

connections thoroughly check all connections are correct to the


141�

contract circuit diagram.

(2) Check that the correct links are fitted as detailed in the test record

‘MAVR Tests with Test Generator’, sub-section6, or by reference to

sub-section 9.2 of the handbook.

(3) In general faults associated with the voltage monitor card can be

separated into six main categories viz.:

Over Voltage monitor Inoperative (Table 9.4.1)

Continuous Operation (Table 9.4.2)

Maloperation (Table 9.4.3)

Under Voltage Monitor Inoperative (Table 9.4.4)

Continuous Operation (Table 9.4.5)

Maloperation (Table 9.4.6)

Refer to the appropriate section for connective action.

NOTE:

If any card is returned to the works for repair please quote the

Type/Model/Contract numbers that appear inside the MAVR front

door and on the right had side of the mainframe together with the

nature of the fault.

Table 9.4.1 Over Voltage Monitor – Inoperative.

No. Possible Fault. Test. Remedial Action.

1. Output link

not selected.

Check link LK2 is fitted. Correct as

necessary.

2. Trip level set

too high.

Check level as detailed in

9.3.

Reset level if

necessary.

3. Trip signal

overridden

Check wiring between

3/11 & 2/5 – should be

open circuit.

Correct as

necessary.

4. Loss of Power

Supply.



to the auxiliary supply.

Replace

blown-fuse or

correct as

necessary.


142�

5. Monitor card

faulty.

Interchange the monitor

card with a spare.

Replace monitor

card and return

to the works for

repair.

6. Mainframe

failure.

No sensing voltage to

card, 110V a.c. (nominal)

to (20) and (22).

See section 3.4.

Table 9.4.2 Over Voltage monitor – Continuous Operation.


1. Trip level set

too low.


section 9.3.

Reset level if

necessary.

2. Control

card-sensing

failure giving

rise to an

over-voltage

conditions.

See section 4.4. See section 4.4.

3. Monitor card

faulty.


card with a spare.

Replace monitor

card and return

to the works for

repair.

4. Mainframe

failure.


Table 9.4.3 Over Voltage monitor – Maloperation.

No. Symptom. Possible Fault. Test. Remedial

Action.

1. Monitor

operates due to

machine off

‘O.V. Delay’ set

too short.

Check delay

as in section

9.3.

Reset delay

if necessary.


143�

load transients.

2. Monitor

operates but

does not giving

latched

indication.

Monitor

failure.

Interchange

the monitor

card with a

spare.

Replace

monitor

card and

return to

the works

for repair.

3. Local

indication

giving but

relay output.

Inoperative.

Monitor

failure.

Monitor

relay faulty

(RL2 on

Mainframe).

Replace

relay RL2

Table 9.4.4 Under Voltage Monitor – inoperative.


1. Output link

not selected.

Check link LK2 is fitted. Correct as

necessary.

2. Trip level set

too low.


9.3.

Reset level if

necessary.

3. Trip signal

overridden

a) Check wiring

between 3/11 & 2/5 –

should be open

circuit.

b) Remove link LK3.

Correct as

necessary.

If operating when

LK3 removed

then either volts

monitor faulty or

control card is

giving an

overriding output

due to ‘F.F.O.’ or

‘soft start’

circuits-see


144�

section 4.4.

4. Loss of Power

Supply.



to the auxiliary supply.

Replace

blown-fuse or

correct as

necessary.

5. Monitor card

faulty.


card with a spare.

Replace monitor

card and return

to the works for

repair.

6. Mainframe

failure.


Table 9.4.5 Under Voltage Monitor –Continuous Operation.


1. Trip level set

too high.


section 9.3.

Reset level if

necessary.

2. Loss of sensing

signal

Mainframe

failure.


5. Monitor card

faulty.


card with a spare.

Replace monitor

card and return

to the works for

repair.

Table 9.4.6 Under Voltage monitor – Maloperation.

No. Symptom Possible Fault. Test. Remedial

Action.

1. Monitor

operates due to

‘U.V Delay’ set

too short.

Check delay

as in section

Reset delay

if necessary.


145�

machine on

load transients.

9.3.

2. Monitor

operates on

buildup,

and/or

run-down.

Link LK3

missing – no

override

during these

conditions.

Check link

LK3 is

fitted.

Correct as

necessary.

3. Monitor

operates but

dose not give

latched

indication.

Monitor

failure.

Interchange

monitor

card with a

spare.

Replace

monitor

card and

return to

the works

for repair.

4. Local

indication

giving but

relay output.

Inoperative.

Monitor

failure.

Monitor

relay faulty

(RL2 on

Mainframe).

Replace

relay RL2

9.5 LIST OF PARTS (CON'D).

Com-po

nent

Ref.

Descrip-ti

on.

Value. Toleran

ce.

Manuf

actures

rating.

Manufac

turer &

Type

Brush

Ref.

IC1,2 Integrate

d Circuit

ZLD74

1

28781-74

3

RV1 Potentio

meter

5

kohm

±

10%

1W

25

turn

Allen

Bradle

y 80

26564-69

0

RV2, 4 Potentio

meter

10

kohm

±

10%

1W Cloven

clr1206

26631-74

7

RV3 Potentio 2 ± 1W Allen 26564-68


146�

meter kohm 10% 25

turn

Bradle

y 80

0

LED1, 2 LED 100m

A/3V

Litroni

x 21-02

28241-25

1

T1 Transfor

mer

240:

12-0-

12

R.S

196-27

4

25122-37

8


147�


148�

10 MAVR AUXILIARY RACK

10.1 INTRODUCTION

The MAVR auxiliary equipment rack contains item which are

associated with any standard MAVR excitation system but which are

not housed in the MAVRE unit.

The rack contains the following main items:

Electronic manual control system;

Auto follower;

Null balance circuit (an external indicator is required);

Exciter field suppression contactor and resistor;

Auto-manual changeover contactor;

Auxiliary d.c. supply fuses;

Terminals for excitation system connections and all MAVR

multicore cables;

Slave relays for MAVR limiter and fault signals.

This handbook section covers the auxiliary equipment rack for use

on single MAVR system in which manual control is selected either

manually by an operator or automatically if AVR d.c. supply fails, or

excitation monitors are fitted to the AVR.

10.2 SPECIFICATION

10.2.1 Excitation Supply Voltage

The unit will accept nominal supply voltages in the following ranges;

150V 200Hz ±15%

180V 240Hz ±15%

220V 400Hz ±15%

264V 480Hz ±15%

220V 50Hz ±10%

Refer to section 8.3 for correct links selection.


149�

10.2.2 D.C. auxiliary Supply

The unit will accept d.c. auxiliary supplies in the following ranges:

24V +15% -20%

48V +15% -20%

125V +15% -20%

220V +10% -10%

Refer to section 8.3 for correct link selection.

10.2.3 Output Rating

1) current

15 amps continuous at 65℃

18 amps continuous at 55℃

2) Voltage

The maximum output voltage is the lowest of the following:

(1) 0.4 X a.c supply voltage

(2) 100V d.c. (LK7 omitted)

(3) 75V d.c. (LK7 fitted)

3) The generator power factor: lag 0.6－lead 0.9

10.2.4 Field Voltage Control

1) Adjustment Range

The controller regulates the exciter field voltage to a constant level

which is continuously adjustable between zero and the maximum

specified in section 8.2.3 2).

2) Remote Adjustment

Adjustment of excitation field voltage is achieved by energizing

either a 'raise' or 'lower' relay on the unit. These relays should be

energized from the d.c. auxiliary supply.

3) Local Adjustment

As a commission/testing aid, miniature pushbuttons are provided on

the printed circuit to raise and lower the set point.


150�

4) Travel Time

The time taken for field voltage to be adjusted between minimum

and maximum limits in 60 seconds.

5) Automatic Reset to Minimum

When the unit is energized during run up, the set point will be

automatically set to zero.

10.2.5 Auto Follower

In the normal operating mode, When the excitation is being

controlled by the MAVR, The output of the manual controlled is

automatically adjusted to match the output of the MAVR, enabling

control to be switched from the AVR to manual with negligible shock to

the system.

While either manual raise or lower control is being operated The

action of the auto follower is temporarily inhibited.

The accuracy of the auto follower for a temperature variation of ±

15℃ will be better than

1) ±2 % at 100 volts output from the AVR.

2) 10% at 10 volts output from the AVR

Where VLA = line voltage on AVR control just before select manual

control

VLM = line voltage on manual control

10.2.6 Inhibit Follower Facility

A relay is provided which, When energized from the auxiliary d.c.

supply, will inhibit the operation of the auto-follower.

This relay is normally energized when manual control is selected and if

an AVR excitation limiter operates when in auto control. When this

relay is energized, the set point of the manual controller will remain

constant unless adjusted by raise/lower controls.

%)(100VLA

VLAVLMaccuracy


151�

10.2.7 Minimum position Indication

A relay is fitted which is energized if the manual controller set point

is at minimum and the manual output is zero.

10.2.8 Null Balance Indication

An output is provided for a 0.5-0-0.5 mA, center zero ammeter.

When the output of the manual controller is matched to the output

of the AVR, balance is indicated by the meter reading zero.

10.2.9 Isolation

There are three groups of terminals on the unit VIZ

1) a.c. supply terminals

2) d.c.. auxiliary supply terminals

3) relay output terminals

These groups of terminals are electrically isolated, both from each

other and from the earth terminal on the frame.

10.2.10 Auxiliary Contactors

Auxiliary contactors are provided for indication/monitoring of the

excitation system. The function and ratings of these contacts are shown

below.

Function Type and Rating

Excitation Tripped

Manual/Auto selected

AVR fault monitor tripped

AVR limiter operating

Manual at minimum position

Changeover 200V 0.07A D.C.. time

constant ≤40 ms


(Reference is made to 0NQ.162.121 and 0NQ.351.018)

[Number is brackets( ) refers to printed circuit board edge connections,

and all voltage levels are relative to TP1]


152�

10.3.1 Electronics Power Supply (T1,DB1,Z2,Z3,Z4,RL1,etc)

The a.c supply for the Electronics Power supply is derived from the

PMG This voltage is applied to the primary of transformer T1 via fuse

FS1, links LK1 to LK5 being used to select the PMG voltage as

following:

Nominal PMG

voltage (±

15%)

Fit Links Omit links

264V LK5,LK4 LK1,LK2,LK3

220V LK5,LK2 LK1,LK3,LK4

110V LK1,LK2,LK3 LK4,LK5

The secondaries of T1 are used via diode bridge DB1 to provide

positive and negative unregulated and three stabilized rails.

R53,C14,R49and Z2 provide the positive unregulated supply for the

pulse circuit and the +15V regulated supply (TP2) for IC1 and IC2.

R51,C15,R52 and Z3 provide the negative unregulated supply for RL2

and the -15V regulated supply (TP3) used for IC1 and IC2.

The -6.2V rail (TP4) is derived from the -15V rail via R50, C13 and

the contact of relay RL1. The coil of RL1, with R48 in series, is

connected between the +15V and -15V rails. This ensures that the -6.2V

rail, which is used for the digital reference and logic, is only available

when the 15V positive and negative rails have been established.

10.3.2 Manual Control Regulator (IC2, T2,VT1,VT2,SCR1,etc)

The manual control regulator output is derived from the PMG

supply and takes the form of a half wave, phase controlled supply. The

current path during the period when the terminal 3 is positive WRT

terminal 4 is as follow:

From terminal 3 via FSC-1 and FS3 to thyristor SCR1 then via

ECC-1, DB1 and the contacts FSC-4, 3 and 2 to terminal 5 and the


153�

exciter fields.

From terminal 2F2 of the field, the path is the MAVR field pick-up

resistors and back via terminal 24 and DB2 to terminal 4.

Phase control of SCR1 is achieved as follows:

IC2 is an operational amplifier arranged as a high gain inverting

amplifier. The input is connected to the manual output via the

attenuating and filtering components R30,R31,R32,R33 and C6. This

provides a positive input which is balanced against the negative input

provided by the digital reference from IC6,IC7 and IC8.

The output voltage of IC2 is determined by the difference between

the manual output and reference voltage, a low manual output

producing a high voltage at TP5, and conversely, a high manual output

producing a low voltage at TP5.

The output voltage of IC2, measured at TP5 is limited between

approximately -0.5 volts and +10 volts by D5,D6,Z1 and R39.

The thyristor firing pulse is produced when VT1 is turned on which

can only occur during the period that the thyristor is forward biased.

The phase reference signal supplied to terminal 23 on the electric

board is connected to the anode of the thyristor. When this is negative,

transistor VT2 is turned on via R41, and the voltage at TP8 is clamped

to approximately -0.5 volts due to current flowing through D9,VT2 and

R40 to the negative rail. This prevents VT1 from being turned on.

During the period that the thyristor is forward biased, D13 conducts

and VT2 is turned off.

This allows the voltage at TP8 to rise, at a rate determined by the

output voltage IC2, and the time constant set by R35 and C7.

An increase in the voltage at output of IC2 due to a low output from

the manual regulator, cause VT1 to turn on earlier, and the thyristor to

fire earlier. This tends to restore the manual output to the correct level,

at which point the manual and reference signals at the input to IC2 are


154�

balanced, and the output voltage of IC2 falls to a steady state level.

The pulse circuit operation is described below:

As the base of VT1 begins conduct at approx. 0.5 volts, collector

current starts to flow. Positive feedback via the pulse transformer T2,

causes VT1 to turn on rapidly which produces a positive pulse in the

output winding which fires the thyristor via terminal 8 on the printed

circuit board.

The pulse energy is provided mainly by C9 and as the voltage

across the pulse transformer falls a point is reached when there is

insufficient feedback to hold VT1 on. A this point the collector voltage

begins to increase, which is followed by rapid turn off due to the effect

of the feedback. Diode D11 provides a path for the stored energy in the

core of the pulse transformer. Meanwhile C9 charges up again through

R49 and as soon as the pulse transformer winding reverse voltage

reaches zero, the cycle repeats itself and another pulse is given.

As a result a train of pulse is applied to the gate of the thyristor.

10.3.3 Digital Reference (IC6,IC7 and IC8)

IC6,7 and 8 form a twelve bit up-down counter controlled by the

raise/lower section.

The 12 outputs, Q1 to Q4 on each IC, are connected to a network of

resisters R76 to R95. The arrangement provides reference signal which

is adjustable in 4096 steps from 0 to approx. 400 micro amps. The

power supply used in both the digital reference and raise/lower logic is

-6.2V so a logic '1' state is at 0V and a logic '0' state is represented by

-6.2V relative to TP1. The up-down counter is in the fully 'up' state

when all of its outputs are a logic 1 but in this state the digital reference

will provide zero current drain and therefore from the point view of the

manual control, it is at the minimum level. Equally when the counter is

in its fully 'down' state the outputs will be at logic 0(-6.2V) and provide

the maximum current for the reference. The above means that an 'up'


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count reduce the reference current and thus reduces the manual output

while a 'down' count increases the manual output. Notwithstanding the

above all the controls provide for the unit are arranged and labeled

such that for instance a 'raise' signal will increase the manual output

even through it has to generate a 'down' count to do so.

The resistors R76 to R95 are arranged to give a virtually monotonic

output to the counter. They are chosen to give powers of 2 reductions

from the Q4 output of IC6 (the most significant bit) right down to the

Q1 output of IC8(the least significant bit).

10.3.4 Raise/lower and Logic (IC3 to IC5, DN1,RL3 to RL5)

The digital reference described in the previous section needs to be

adjusted, while the unit in use , in several different ways. The

requirement of this logic function are as follow:

(1) While Operating in Auto

The auto-follower raise/lower output must function but will be

inhibited temporarily by the operation of the manual

raise/lower controls both remote and local. The auto-follower

output must also be inhibited by the operation of the MAVR

excitation limiter.

(2) Operating in manual

In this case the auto-follower output will be inhibited

completely and only the manual raise/lower controls both local

and remote will adjust the reference.

Note: Throughout the following description, the terms 'logic

1' and 'logic 0' will be used in the normal way but it must be

kept in mind that the actual voltages:

Logic 1 is 0V

Logic 0 is -6.2V

1) Reset Circuit


156�

IC5 (d) together with R37 and C31 are arranged such that as

the logic power rail establishes (as RL1 energized -see section 8.3.1)

the output of IC5 (d) will go to logic 1 for a short time before

dropping to and remaining at logic 0. This signal is connected to the

preset enable pins of the counter IC6 to IC8 and has the effect of

setting the counter to the state determined by its 'Jam' input, in this

case to full count which represents the minimum hand control

output.

2) Clock and Gate Circuit

IC5(c) generates a continuous train of clock pulses the

frequency of which is determined by C29, R70 and RV4. These

pulses are routed through the gate IC4 (d) to the clock input of the

counters IC6 to IC8. Pin 12 of IC4(d) gives control of the gate.

Logic 1 on this pin enable the gate and allows the clock pulses

through and logic 0 will prevent the passage of clock pulses.

3) Latch Circuit

IC5(a) and IC5(b) are arranged to give a latch circuit. The

output from this latch from pin 3 of IC5(a) is fed to the up/down

inputs of the counter IC6 to IC8.

The latch is such that a momentary logic 0 at pin 1 of IC5(a)

will give a logic 1 on the latch output and cause the counter to count

up. The latch output will remain in this state until a logic 0 is

momentarily applied to the other latch input on pin 6 of IC5 (b) in

which case the output will become logic 0 and cause the counter to

count down.

If a logic 0 input is applied to both inputs of the latch then the

output will be a logic 1 and give an up count on the counter.

R68 and R69 are pull-up resistors so that, in the absence of

inputs to the latch, both inputs are held at logic 1.


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4) Relay Buffers

Relay RL3,RL4 and RKL5, which are on the p.c. board, are

used as buffers between the external signals and the electronics.

They are energized from the auxiliary d.c. supply to the unit.

Provision is made with LK8 to LK13 for three d.c. supply voltages.

D.C.. SUPPLY FIT LINKS OMIT LINKS

125V +15%/-20% ----- LK8,9,10,11,12,13

48V +15%/-20% LK9,10,12 LK8,11,13

24V +15%/-20% LK8,11,13 LK9,10,12

Relay RL3 is energized from pin 12 on the PCB. When an

external 'lower' signal is given.

5) Raise/Lower and Inhibit Circuit

(1) Operation in Auto (Auto follower operation)

In the absence of any external raise or lower signals, the

output of both IC3(b) and IC3(c) will be at logic 1.

In auto RL3 will be de-energized unless the excitation limiter

operates, and the output of IC3(a) will be at logic 1. This

enables IC3(d) and IC4(a).

The output of the auto follower comparator at IC1(b) pin

1 is applied to the input of IC4(a) at pin 2. When the output of

the auto is most negative, the output of IC4(a) will be at logic 1.

This will produce a logic 0 output from IC3(d) resulting in

(i) a Logic 1 at the output of IC4(c) which enables the clock

gate.

(ii) The latch IC5(a) and (IC5(b)) gives an 'up' signal to the

counter.

If the output of the auto follower comparator is positive,

IC4(a) output will be logic 0 which will cause the latch to give a

'down' signal to the counter and again enable the lock gate via

IC4(b).


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While operating in the auto follower mode as described

above, the counter is operating continuously and the up/down

signal is alternating every few clock pulses as the system keeps

the manual output matched to that of the MAVR. The slight

oscillation may be visible on the null balance meter.

Auto follower operation can be interrupted in several

ways:

(i) The counter may reach the fully down or fully up state. In

either case the 'carry out' pin 7 of IC6, goes to a logic 0 and,

via D23, clamps further clock pulses until released by the

up/down signal being reversed.

(ii) A MAVR limiter may operate or control may be

transferred to manual by a external signal.

(iii) An external (or logical) raise or lower signal RL4-1 or PB2

will close and IC3(c) will produce a logic 0 output which

disables IC3(d) and IC4(a) again inhibiting the auto

follower action. A lower signal produced the same effect via

IC3(b)

(2) Operation in Manual

As explained in (ii) above, relay RL3 will be energized

when operating in manual and the auto-follower action will be

inhibited. An external raise signal will energized RL4 and

RL4-1 will close producing a logic 0 at the output of IC3(c).

This will operate the latch (IC5(a) and IC5(b)) causing it to give

a down signal and at the same time, via IC4(b), enable the clock

gate. Clock pulses will continue to reduce the counter level until

the external raise signal is removed.

An external lower signal will energized RL5 and RL5-1 will

close. This produces a logic 0 at the output of IC3(b) which

operate the latch (IC5(a) and IC5(b) causing it to give a up


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signal and at the same time, via IC4(c) enable the clock gate.

Clock pulses will continue to increase the counter level until the

external lower signal is removed.

These raise and lower operations can be accomplished

locally by operating the pushbuttons on the PC board.

Simultaneous operation of raise and lower controls gives an

up count causing a reducing a reduction of manual output.

When the counter reaches fully up or fully down state, the

same process occurs as explained in 8.3.4. 5) (1) to inhibit

further clock pulses.

10.3.5 Auto Follower

IC1(a) is an amplifier the gain of which is adjustable using

potentiometer RV1. The input to this amplifier is supplied from the

MAVR output attenuated and filtered by R1,R2 and C3. The output,

Which is inverted, is fed via R6 to the inverting input of IC1(b).

The manual output, attenuated and filtered by R7, R8 and C4, is also

applied via R9 to the input of IC1(b). This amplifier is arranged as a

high gain inverting amplifier and acts as a comparator. The difference

between the auto and manual outputs thus appears at the output of

IOC1(b). This output is fed via R11 to IC4(a) where it provides the

raise/lower signal for the digital reference.

Two controls are provided to set up the balance between the

outputs of the AVR and manual regulator. RV1 adjusts the gain IC1(a)

and is used to compensate for component tolerances in the attenuation

circuits. RV2 can be used to give a constant negative bleed to the input

of IC1(b)

which is adjustable, and in most applications will be set to minimum, or

close to minimum.

10.3.6 Null Balance Detector (IC1 (c), IC1(d) etc.)

IC1(c) is arranged as a low gain, inverting amplifier which is


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supplied from the auto output after attenuating and filtering with

R18,19 and 20 and C23. The inverted output is fed via R23 to the input

of IC1 (d). The manual output after attenuation and filtering with

R24,R25,R26 and C25 is also fed to the input of IC1 (d) which is

arranged as a high gain inverting amplifier. IC1(c) and (d) are

analogous in operation to IC1(a) and (b) in the auto follower circuit but

the output of IC1 (d) supplies via R28, an external center zero

millimeter. This instrument must be a moving coil type with a sensitivity

of 0.5 – 0 – 0.5 mA.

As described in Section 10.3.5, potentiometers RV3 and RV2 are

used to achieve satisfactory balance throughout the working range of

the unit.

10.3.7 Minimum Position Indicator (IC9 VT3 VT4 RL2 etc.)

This circuit gives a relay output signal and local LED indication

when the manual output is at the minimum level.

The eight most significant of the twelve outputs from the digital

reference are taken to an eight input and gate IC9. When all eight

inputs are at logic 1 then the reference counter is virtually at the

minimum position and the output of IC9 will be at logic 0.This will turn

or transistor VT4 via VT3. LED1 and RL2 will be energized given local

and remote indication that the reference is at the minimum position.

R99, R100 and C32 provide a signal to VT3 base, which is proportional

to the output of the manual regulator. This ensures that minimum

position indication is only given when the digital reference and the

manual regulator output voltage are at minimum.

10.3.8 Field Suppression

Incorporated in the rack is a block contactor (FSC) and a resistor

(FSR) used for suppression of the exciter field. Three contacts of FSC in

series are used, each of these contacts having a section of FSC connected

across it.


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As these contacts open to suppress the field, the current flows

through the resistor FSR giving rapid decay of exciter filed current. A

fourth contact of FSC is used to break the A.C supply from the

PMG.

The contactor is mechanically latched so that a failure in the coil

supply will not product any change in the contactor state.

When the contactor is in the tripped condition, (recognized by the

button on the latching mechanism being ‘in’ ) the field is suppressed.

10.3.9 Smooth Transfer

As described in the previous sections, the auto follower action

ensures a smooth transfer from auto to manual but smooth transfer

from manual to auto is not provided as standard. However it can be

achieved as follows:

When operating in manual control, contact ECC-7 is open to

remove the PMG supply to the MAVR power circuit. (The MAVR

electronics supply is remains energized via terminals 3/6 and 1/11).

To obtain smooth transfer, a switch (arranged with a spring

return to open mechanism) should be connected between terminals 26

and 27 on the unit. When the switch is closed , the supply is restored to

the MAVR power circuit and the AVR output will be present at terminal

25 on the unit.

The null balance indication facility will now operate although

when operating in manual control , the indicator will invariably settle at

either end of the indicator scale.

To transfer from manual to auto with minimum shock the MAVR

datum should be adjusted to correspond to the generator or bus bar

voltage. At this point, the null balance indicator reading will suddenly

reverse. By making slight adjustments to the AVR datum and observing

the null balance indicator it is possible to confirm that the AVR and

manual regulator are set to give the same output voltage at this point


162�

transfer to the AVR will be achieved with minimum system shock.

10.4 COMMISSIONING

This section should be read in conjunction with the general

commissioning procedure, section 11.

10.4.1 Preliminary Tests

1) Remove front cover of auxiliary rack and retain for subsequent

replacement.

Check that the correct links are fitted by reference to ‘ The Setting

Record of MAVR Testing with Test Generator’ item 6.

2) Care should be taken before connecting any supplies to ensure that

all the connection to the unit and MAVR are correct by reference to

the contract schematic diagram. The polarity of the D.C supply

should also be checked.

3) Connect the D.C supply to the excitation system.

4) Operate the manual/auto switch (local and remote). When

‘manual’ is selected the button on the latch of ECC should be

‘out’ and relay ECCS should be energized and its indicator ‘ON’ –

when ‘auto’ is selected the ECC latch button should be ‘IN’ and

relay ECCS should be de energized and its indicator ‘OFF’. Check

that any external indication of excitation mode are correct.

5) Operate the protection relay or arrange by temporary wiring to

provide ‘Excitation ON’ and ‘Excitation Trip’ signals. When

excitation is ‘on’ the button on the latch of FSC should be ‘OUT’

and relay FSCS should be energized and its indicator ‘ON’. When

excitation is tripped the FSC latch button should be ‘IN’ and FSCS

should be de energized, its indicator off.

While carrying out these tests check the operation of local and

remote excitation ON/OFF indications.

6) With the excitation mode switch in ‘Manual’ use AVO meter or


163�

equivalent to check that the ‘Transfer’ Switch (if fitted) is correctly

connected in that rack terminals 26 and 27 are linked only when

the switch is operated.

7) Operate the manual raise/lower switch and check with an AVO set

to the appropriate D.C. voltage range, that with respect to terminal

2 (-ve) terminal 11 is (+ve) when a ‘raise, signal is given, and that

terminal 12 is (+ve) when a ‘lower’ signal is given.

10.4.2 Manual Control

1) Remove and isolate the exciter field connections from the MAVR

and the MAVR auxiliary rack. These are :

(1) The positive connection at terminal 5 on the M.A.V.R.

auxiliary rack.

(2) The negative connection at terminal 1/14 on the multi core

connection terminals of the auxiliary rack.

2) Connect an AVO or similar suitable meter set to 100V D.C. range,

positive to terminal 5, negative to terminal 1/14. By operating the

excitation mode switch select the ‘Manual’ mode (ECCS energized

and check that) FSC is in the ‘ excitation ON’ state (FSCS

energized).Turn the excitation off using the switch in the PMG

supply.

3) Run the generator up to rated speed and by using the switch in the

PMG supply switch the excitation on. The output voltage on the

AVO meter should be zero and local (LED on P.C. board) and

remote indication of ‘manual at minimum ‘ should be given.

4) By operating the manual raise / lower control switch check that the

output voltage can be adjusted from zero to a level at least equal to

the full load exciter field voltage.

The generator output voltage during this test should remain low at

the residual level since the exciter field is disconnected.

5) With the output at 30 volts switch the excitation off using the PMG


164�

supply switch and check that the output is reduced to zero. Check

that when the PMG supply switch is switched ON the output

remain at zero.

Turn the switch to OFF.

6) Shut down the generator and replace the field connections removed

in 1) above .Run the generator up to speed, turn the excitation on ,

and check that smooth control of the generator output voltage is

obtained using the manual raise / lower switch.

Proceed with section 10.4.3 following commissioning of the MAVR.

10.4.3 Final Commissioning (To be completed following commissioning of

MAVR.)

1) Smooth Transfer Auto to Manual

Run the generator at rated speed and rated voltage in auto control.

Take a careful note of the line voltage. Use the excitation mode

switch to transfer to manual. Note the new line voltage and if

necessary adjust RV1 on the MAVR auxiliary rack P.C. board.

Slightly to reduce the auto / manual line voltage difference.

Clockwise adjustment of RV1 increases the manual output and vice

versa. RV2 is normally set fully anti-clockwise.

Switch control between manual and auto, and optimize RV1 to

produce minimum change in line voltage when switching between

both mode of control.

Select ‘auto’ and adjust RV3 as necessary to obtain zero (mid scale)

reading on the null balance meter.

Run in AVR control.

Load the generator either individually or by paralleling to a larger

system.

Check that as excitation changes, the null balance indicator is

maintained at the zero position. If necessary, operate the voltage

setting control on the MAVR to vary the VAR’ s, to confirm the auto


165�

follower action.

Select manual control and check that there minimum change in

excitation on switching from Auto to Manual.

To obtain smooth transfer from manual to auto, the procedure

described in 2) should be followed.

2) Smooth Transfer Manual to Auto.

This may be achieved by using a smooth transfer switch which

should be connected between terminals 26 and 27 on the auxiliary

rack . The switch must be arranged so that it is spring loaded to the

open state.

The following sequence should be carried out starting in manual

control:

(1) Check that the machine line voltage is within 5% of nominal.

(2) Turn the motorized voltage setting rheostat (MVSR) on MAVR

fully anti- clockwise.

(3) The null balance meter should read fully to right or left. Note

its position.

(4) Close the smooth transfer switch and hold it closed.

(5) Slowly increase MAVR until the reading on the null balance

meter suddenly reverses. Then adjust MVSR until the null

balance meter reading is zero.

(6) Select auto control and release the smooth transfer switch.

Excitation will be change from ‘Manual’ to ‘Auto’ smoothly.


Before attempting to trace suspected faults on the M.A.V.R.

auxiliaries

rack, the basic tests outlined on section 13.should be followed. In

the event of the auxiliary equipment rack being suspected faulty, the

following tables should assist in locating the fault and effecting a


166�

remedy.

The faults full generally into three categories:

Contactor and Relay faults Table 10.5.1

Faults occurring when in manual control Table 10.5.2

Fault associated with the Auto Follower and Table 10.5.3

Null Balance indicator.

10.5.1 CONTACTOR AND RELAY FAULTS

No. Symptom Check Remedial Action

1) FSC closed (button

on latching unit

OUT FSC closed)

If closed check all field

circuit wiring. If not

closed perform 2). 3).

4). 5).

2) Check PMG fuses and

links in pilot exciter

terminal box

Replace if necessary

3) D.C supply to terminal

1 (+ve) and 2

Ensure supply present

and correct voltage.

4) D.C fuses FS1 &FS2 Replace if blown

5)FSC control switches

or contacts


1. Cannot

Excite machine

on manual or

auto.

6) Check FSC latches

closed when close signal

given

If D.C. volts applied to

close coil of contact,

contactor should close

& lated. If not-

contactor is faulty


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2. Excitation

will not trip

1).Volts applied to FSC

trip coil when trip signal

given.

If correct volts present

and contactor does not

trip (button on latching

unit goes IN).

Contactor is faulty .If

volts not

present ,perform

checks 10.5.1 1. 3). 4).

5).

1).ECC latches closed

when manual select

switches operated

2). As 10.5.1 1. 3). 4).

3). Check ECC control

switches / contacts

If ECC closes check

wiring in rack

associated with manual

power circuit.

3.Cannot select

Manual

4).Check ECC latches

closed when manual

select switch operated.

If D.C volts applied to

close coil of contactor it

should close & latch .If

not- contactor is faulty.

1). Check MAVR

monitors are reset

Reset monitors before

attempting to select

Auto.

4. Cannot

select Auto

2). Check ECC latches

open when Auto select

switch operated.

If D.C. volts applied to

trip coil of contactor it

should trip. Ensure

that continuous

Manual select signal

not being given.

1).Check FRS energizes

when fault monitor

operates.

5. Manual not

selected when

MAVR fault

Monitor

operates.

2). Check FRS-1 ECC-6

circuit.

Check wiring from

MAVR to FRS


168�

1).ECCS energizes when

manual selected

6. Auto

follower not

inhibited when

in manual.

2). ECCS-3 closes to

apply +ve D.C to

energized RL3 on P.C.

board.

Check & rectify wiring

as necessary

1). Ensure LRS

energized when MAVR

limiter operates.

7.Auto follower

not inhibited

when MAVR

limiters

operate.

2) Ensure LRS-1 closes

to apply +ve D.C. to

energize RL3 on P.C

board.

Rectify as necessary

10.5.2 FAULTS OCCURRING WHEN IN MANUAL CONTROL


1). Check correct links

fitted.

Alter if necessary.

2). Check semiconductor

fuse FS3 in rack.

Replace if

necessary

3). Check fuse FS1 on P.C

board.

Replace if

necessary

4). Check ECC energized,

the button on the

contactor being ‘OUT’.

Check contactor

control wiring.

1. Zero output.

5). Check FSC closed, the

button on the contactor

being ‘OUT’

Check contactor

control wiring


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6). Operate raise PB2 on

P.C board

If this produces

output, check

remote raise switch

wiring energizes

RL4 on P.C board.

Rectify as

necessary.

7). Check remote switches

not giving permanent

lower signal.

Rectify if necessary.

8). Test thyristor ref.

Section 5.4.

Replace if

necessary.

1). Check that local

adjustment operates.

If local adjustment

operational check

remote control

switches energize

RL4 (raise) and

RL5 (lower) on P.C

board. Rectify as

necessary.

2. Remote

adjustment

non-operational.

2). Check voltage selector

links.

Rectify if necessary.

1). Test thyristor ref.

Section 5.4

Replace if

necessary.

3. Excitation flat

out.

2). Check LED 1 come on

when unit is switched on

indicating ‘Manual reset

to minimum’

If not, P.C board

faulty .Fit

replacement.


170�

3)Check continuous raise

signal is not being given

by remote switches

causing RL4 on P.C

board to be continuously

energized.

Rectify wiring if

necessary.

4. Cannot obtain

full load

excitation.

1).Check that link 7 is

fitted.

Lower output if

fitted.

1). Check exciter field

voltage is constant. If this

is so line volts fluctuating

will be due to speed or

load variation.

5. Line voltage

fluctuates when on

manual control.

2). Check all wiring is

sound no loose

connections.

Replace as

necessary.

10.5.3 AUTO FOLLOWER FAULTS


1. Line voltage

changes following

transfer to manual

at light loal.

1). Check load steady and

that null balance

indicator is stationary

prior to transfer.

Refer to section

10.4.3. 1). to set up

RV1 on P.C .board.

1). Check load steady and

that null balance

indicator is stationary

prior to transfer.

2. Line voltage

changes following

transfer to manual

when load.

2).Check RV2 fully

anti-clockwise.

Reset and repeat

10.4.3. 1). If

necessary.


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3). Check whether voltage

change gets worse when

transferring to manual at

hight loads.

Rotate RV2 on P.C.

board 10%

clockwise then

reset RV1 to give

minimum voltage

change on transfer

to manual. Increase

setting of RV2 to

improve further if

necessary.

3. Null balance

indicator not at

zero when output

of manual

controller

matched to output

of AVR.

1).Set up RV3 on P.C.

board.

Refer to 10.4.3. 1).

10.6. CONSTRUCTION TRANSPORT AND INSTALLATION

10.6.1 CONSTRCTION

The unit is housed in a standard equipment rack 19” wide. See

drawing C11-1. All equipment is mounted on a steel back plate and an

anodized aluminium plate provides the front cover of the unit.

Perforated metal cover are fitted to the top and bottom of the unit.

Two rows of terminals type D1 are fitted to the rear panel which

are suitable for cables up to 6 mm2.

These terminals are for M.A.V.R. multi core terminations and

other connections to excitation system.


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10.6.2 INSTALLATION

The unit any be installed in a cubicle directly above or below its

associated M.A.V.R. unit.

It is recommended that at least 150mm of free space is provided

above and below the unit, or if mounted with the M.A.V.R., above and

below the pair of units. This is necessary to provide adequate air

circulation for cooling. It must be noted when installing that the multi

core between M.A.V.R. and rack is 3m long.

10.6.3 TRANSPORT

If the cubicle is to be transported with the rack installed; the rack

should be supported underneath to relieve the stress on the mounting

flanges. It may be seperately packed for transportation.

10.6.4 WEIGHT

The complete unit weight 17kg.


173�


174�


175�

11 COMMISSIONING

11.1 GENERAL

Prior to commissioning the M.A.V.R. unit it is important to

complete commissioning of the protection system for generator and

associated power equipment. Having verified that these are correct the

following preliminary checks should be made on the excitation system:

1) Check the PMG output or alternatively the excitation transformer

is correct wired.

2) Check the sensing signals (C.T’ s and P.T’ S) are correct in polarity

and phasing.

3) Check the exciter field is correctly wired.

4) Check all wiring external to the M.A.V.R. is correct to the contract

circuit diagram, and sound.

5) Check excitation contactors, logic, manual control and any other

auxiliary equipment have not been disturbed in transit and that

wiring is sound.

6) Visually check the M.A.V.R. unit has not been physically damage on

transit to site, ensure that outgoing plug in cards are correctly

aligned and inserted fully.

7) Check that the correct links are fitted in the M.AV.R. unit as

detailed in the setting record for M.A.V.R. Testing With Generator

sub- section 6.

11.2 THE MAVR UNIT IS THEN READY FOR

COMMISSIONING

11.2.1 COMMISSIONING A SINGLE EXCITATION SYSTEM WITH

M.A.V.R AUXILIARY RACK (ELECTION MANUAL CONTROL)

1) With the generator at standard, complete the following section:

(1) 3.3 Commissioning of the MAVR mainframe.


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(2) 5.3 Commissioning of the Auto Power Card.

(3) 10.4.1 Preliminary Commissioning of the MAVR Auxiliary

Rack.

3) Commissioning the manual control of MAVR Auxiliary rack as

described in section 10.4.

4) Commissioning MAVR Control card, section 4.3.

5) Commissioning MAVR Excitation Limiter Card, section 6.3.

6) Commissioning MAVR Power Factor Control Card, section 7.3.

7) Commissioning MAVR Auxiliary Rack, section 10.4.

8) Having complete all the appropriate sections above a final check

should be made to ensure that all external controls and indication

function correctly.

Note: The above procedure must be followed during

commissioning.


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12 FAULTY FINDING

12.1 GENERAL

If a MAVR unit does not function correctly, a test sequence is

recommended in which the generator and external wiring are first

thoroughly checked before it is assumed that the fault lies in the

electronic equipment .The fault finding procedure is designed to enable

faults to be found quickly. It is essential, therefore, to follow the order in

which they are presented. In the event of finding a fault on any part of

the MAVR the company strongly recommends that no attempt is made

to repair the unit, but is replaced by a spare which should be

re-commissioned according to the relevant section of this handbook.

The fault unit should be returned to the Works for repair.

12.2 PRECAUTIONS

Meggers Flash Testers and Bell Sets must not be used to check any

equipment connected to or incorporating semiconductor.

If these instruments are to be used to check any equipment,

isolation from all semiconductor devices must first be ensured. In the

case of the MAVR either remove all the plug in multi cores from the

rack or short together all the individual cores of all the multi cores.

When the MAVR auxiliary rack is fitted , it is recommended that ,

when on site flash testing is required ,all outgoing cables are

disconnected and the terminals at the rear of are linked together prior

to flash testing.

12.3 PROCEDURE

Before commencing fault finding on the MAVR unit the following

preliminary checks should be carried out.

1) Check correct operation of the generator, i.e. PMG output available

( if applicable ), the field and sensing signals are correct etc.


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2) Check all wiring associated with the excitation system.

3) Check all contactors switches and other external components

associated with the MAVR rack(s) or plate.

4) Check that the correct links are fitted in the MAVR unit as detailed

in the test record ‘MAVR Tests with Test Generator ’ sub-section 6.

Having completed these preliminary checks the fault can be

assumed to be internal to the MAVR unit. In this event the nature

of the fault will generally fall into one of the following categories:

(1) Loss of excitation in ‘manual’ control: for rack mounted

auxiliaries with electronic manual control. (see Table 10.5.2)

(2) Over excitation in ‘manual’ control: for rack mounted


(3) Excitation fluctuates in manual control: for rack mounted


(4) Loss of excitation in ‘auto’ control. (see Table 12.3)

(5) Over excitation in ‘auto’ control. (see Table 12.3)

(6) Instability (see Table 12.3)

(7) Parallel operation instability (see Table 12.3)

(8) Limiter mal operation (see Table 12.3)

(9) VAR control mal operation (see Table 12.3)

(10) Monitor mal operation (see Table 12.3)

(11) General system operation faults (see Table 12.3)

Each category has an associated table which details the

appropriate action to be taken, cross referring to the individual

MAVR unit fault finding sections. By following the sequence

through the source of the fault should be located and the cause

remedied.

In the event of the fault not being located, or in cases of

difficulty or doubt, contact:


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Table 12.3.1 Loss of Excitation in ‘Auto’ Control

No. Check Remedial Action

1. PMG output to MAVR input

(1/3 to1/7 )should be 220V A.C

Correct wiring, excitation

switch or blown fuse as

necessary

2. MAVR output voltage present

at 1/1 and 1/10.

1) Auto power card fault

–see section 5.

2) Control card fault –see

section 4.

3) Mainframe fault –see

section 3.

3. Field current flows when

MAVR field output high

Correct field circuit

connection

4. Check generator Possible rotating diode

failure or open circuit field.

Table 12.3.2 Over Excitation in ‘Auto’ Control


1. Check sensing voltage to

MAVR nominally 105V A.C


2. Check FS3,4 on MAVR ( i.e.

sensing fuses )

Replace blown fuses

3. Check ‘Auto’ control

components

1) Auto Power card fault -see

section 5.

2) Control card fault –

section 4.

3) Mainframe fault – see

section 3.


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Table 12.3.3 Instability – Single Running


1. Check if unstable on manual

control (Electronic manual

system).

Refer to table 10.2.

2. If unstable in auto control

check stabilizing setting.

If stability cannot be reset

satisfactorily then control

card fault – see section 4.4 or

mainframe fault –see section

3.4

Table 12.3.4 Parallel Operation Instability


1. Check C.T &P.T phasing. Correct as necessary.

2. Check correct mode links

selected i.e. ‘Q.C.C’ or ‘Line

Drop Comp.’

Correct as necessary.

3. Correct control card and

mainframe.

Control card – see section 4.4

and mainframe – see section

3.4.

4. Check that machine running

within the limits of the

operating chart.

Refer to section 3.4, 6.4, 10.4

and re-adjust if necessary

5. Check stability setting of

limiters

6. Check stability on manual

control.

Refer to section 10. If

electronic manual fitted.

.

Table 12.3.5 Limiter Mal-operation


1. Check limiter settings. See section 6.3


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2. Check limiter setting are

consistent with the site re-

quirements.

Confirm with the Works any

revised setting and adjust as

in section 6.3.

3. On a twin system check the

‘smooth changeover’ logic if

over excitation faulty.


4. Check C.T & P.T phasing if

‘Under Excitation’ mal

operating.


5. Check external field current

pick-up signal if ‘Over

Excitation ‘ mal operating –

Direct excitation system only.


6. Check limiter card and

mainframe.

Excitation limiter card – see

section 6.4. Mainframe – see

section 3.4.

Table 12.3.6 VAR Control Mal-operation

No Check Remedial Action

1. Check C.T &P.T phasing Correct as necessary.

2. Check Q.C.C setting on

control.

Adjust if necessary – see

section 2.3

3. With P.F. Control card –

check the auxiliary D.C

supply and PFC latching path

to the MAVR.


4. Check the ‘slug’ and ‘gain’

stabilizing settings of the P.F

Control card.

P.F Control card – see section

7.3

5 On twin system check the

‘smooth changeover’ logic.



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6. Check P.F. Control card P.F. Control card – see

section 7.4

7. Check system voltage is within

±10% of the AVR set point.

Correct on volts settings/

Q.C.C controls if necessary.

Table 12.3.7 Monitor Mal-operation

No. Check . Remedial Action

1. Check monitor settings Voltage Monitor – see section

9.3. Excitation Monitor -

see 8.3.

2. Check monitor settings are

consistent with the site

requirements.

Confirm with the Works any

revised settings and adjust as

in section 9.3 voltage monitor

and 8.3 excitation monitor.

3. Check external override logic

if monitor inoperative.


4. Check external field current

pick-up signal if ‘Over

Excitation’ mal operating –

direct excitation system only.


5. Check C.T & P.T phasing if

‘Under Excitation’ mal

operating.


6. Check monitor cards and

mainframe.

Excitation Monitor card – see

section 8.4. and Voltage

Monitor card – see section

9.4 and see mainframe – see

section 2.4.


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Table 12.3.8 General System Operation Faults

No. System Check Remedial Action

1. System

response

unsatisfactory.

Check control card

stability settings.

Reset controls – see

section 4.4.

2.Excessive

overshoot on

build-up.

Check FAC auxiliary

contact between 2/5 and

2/11.


3.On-load

response

sluggish.

‘If limit’ set too low or

stabilizing too slugged.

See section 4.4

4.Generator

VAR capability

too limited.

Check limiter settings. See section 6.3

5. Single running

voltage droop

excessive.

Excessive Q.C.C Reset Q.C.C as in 4.3

6. Monitor

operation with

voltage or load

transients

Check monitor delays. Reset delay : Voltage

monitor – 9.3

Excitation monitor –

8.3.

7. Monitor

operation before

limiter

operation.

Check relative levels and

delays.

Reset as necessary :

Excitation limiter –

5.3

Excitation Monitor –

6.3

8. VAR control

range limited.

Check system droop is

not greater than 10%.

If less than 10% then

P.F control card is

fault see 7.4.

9.Line volts /

VAR’ s change

excessively.

Check setting up of

balance and offset

controls

Refer to section

12.3.4.


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1).Check voltage

matching between units.

Reset as necessary as

in 4.3

2) Check smooth

changeover logic if

occurring on Excitation

limiter operation.


3). Check operating

levels of Excitation

limiters if occurring

when in operation.


Excitation limiter –

5.3

10. Excessive

shock on

transfer between

AVR’ s on a twin

system.

4). Check auxiliary

supply of standby AVR is

present prior to

changeover.



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13 INSTALATION AND MANTENCE

13.1 MECHANICAL DATAILS

The overall dimension of MAVR and Auxiliary rack are given in

fig 13-1 & fig 13-2 and they are designed for front panel mounting. The

mainframe is aluminium construction with a smoked ‘perspex’ door

hinged on the left hand side. Access to the with draw able cards is by

turning the quarter-turn fastener anti-clockwise and opening the door.

This then reveals the fixed front panel and with draw able cards, the

latter also being secured by quarter-turn fasteners. The fixed front

panel, on the left hand side, caries the fuses and motorized voltage

setting potentiometer (if applicable) and is not intended the

quarter-turn fastener anti-clockwise and pulling the card out. The auto

power card may be damaged if with drawn from the unit whilst the

card is supplying excitation and replacing electronic plug-in cards. To

replace a card first turn the quarter-turn fastener fully anti-clockwise

until tight. For commissioning purpose an extender card and plug onto

the required card and replace the whole into the appropriate card

socket.

The outgoing terminating of the MAVR unit are by up to 4 rear

mounted plugs / sockets to 3 meter of 15 way multi core. To enable a

sound earth to be made to the MAVR mainframe an earthing stud is

also made on the back of the unit.

There are two lines of terminal on the rear of AUX. Rack . One is

designed for connection with cable between MAVR and AUX. Rack.

Anther is used for the outgoing terminations of MAVR unit. An

earthing stud is also made on the rear of AUX. Rack.

The weight of MAVR and AUX. Rack is 17 kg respectively.

13.2 INSTALLATION

The MAVR unit is primarily designed for mounting into any


186�

sturdy panel with a suitable cut-out. It is strongly recommended that

where the unit is to be fitted a cut-out that some form of vertical

stiffening is incorporated behind the panel at each side of the cut-out to

support the cantilevered weight of the unit. The unit also can be

mounted on other appropriated place. It is recommended that at least

150mm above and free space is provided between the main and

Auxiliary racks to provide adequate air circulation for cooling when

packed together. The two units can also be mounted separately.

However, a free space at least 150mm above and below the unit is also

recommended to provide for cooling. The four (or less) multi cores used

interconnect the MAVR unit with the external panel of the excitation

system must have each core individually terminated at a terminal block

whether they are or not. To avoid the eventuality of the outgoing sockets

vibrating loose or being inadvertently pulled loose the retainer should

be pulled over the socket hoods. The 3 meter length of multi cores

should not be shortened excessively as a sufficient length of ‘ free’ multi

core should be left to allow the rack to be with draw prior to the multi

cores being disconnected. As the individual cores of the multi core each

indelibly marked (numbered 1to 15 by words and numerals), if they are

shorted the identification is not lost. If required the earth wire should

be run from the MAVR back mounted stud, with the multi cores to the

earthing bar.

13.3 MAINTENANCE

The MAVR unit is essential completely static apart from the relays,

push buttons and motorized voltage setting potentiometer, and as such

requires very little maintenance.

Every six mouths or during routine station maintenance periods

remove the MAVR unit and visually inspect that it is free of dust and

any other debris In particular check that the motorized voltage setting


187�

potentiometer, associated limit switch and back panel plug-in relays are

function correctly. In the event of excessive dust build-up it should be

carefully removed using a soft brush.


188�


189�


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14 OPERATION

After all commissioning procedure of Mainframe and Auxiliary

Rack have been finished and all Parameters have been set. M.A.V.R

may be operated with a Generator.

14.1 EXCITATION SYSTEM COMMISSION AND OPERATION

14.1.1 Confirm that system is either in constant power factor control or in

constant reactive current control prior to commission. In general the

constant power factor control is selected . However if the capacity of the

grid is small or large VAR is needed. The constant reactive current

control, LK4,LK1 should be omitted with LK2 ,LK3 fitted. If neither of

the control modes is selected .Power factor controller should be latched

during operation.

If the generator is running in single or a few Generators, similar in

capacity, running in parallel. The power factor controller should be

latch.

NOTE: When the N /O contactors of Auxiliary relay ZJ1, connected

between multi cores 2/1 and 2/5 are used for parallel operation, with

circuit breaker closed , multi cores 2/1 and 2/5 will be short- circuited.

Then the power factor control card will go in operation. If no N/O

contactors are used, the power factor control card will not be selected.

14.1.2 Operate “ Auto Excitation” control switch SW4 and set MVSR to preset

level position.

14.1.3 Turn “ Excitation Selector” switch SW1 to “Auto” ,and set the Single /

parallel running control switch SW5 to appropriate position.

14.1.4 There are two mode for Generator voltage build up.

1) Switch on the excitation control switch SW3 as the Generator runs

up to its rated speed, voltage will build up with speed rising . When

the Generator is up to 85% rated speed, voltage reaches its set

voltage.


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2) Run the Generator up rated speed. Then switch on SW3 voltage

will build up quickly with overshoot less than 5% of rated voltage.

14.1.5 After Generator voltage has build-up, use “Automatic Synchronizing

Unit ” or “Hand synchronizing Unit” to hook up the Generator to grid.

14.1.6 When the Generator is running in parallel the set value of power factor

(or VAR power) can be adjusted by ‘level’ potentiometer power factor

control card front panel. Care must be taken that in constant power

factor control the set power factor should not exceed the that on the

Generator name plate; While in constant reactive current control, it

should ensure the Generator not to be overloaded at rated output.

If the power factor control card is switch out of operation, adjusting

MVSR can b change the power factor or reactive current of the

Generator.

14.1.7 Two ways to transfer ‘Auto’ to ‘Manual’ during operation:

1) If power supply fails or Monitors relay operates, ‘Auto’

automatically transfer to ‘Manual’.

2) ‘Auto’ can be manually transferred to ‘Manual’ by turning SW1

(Excitation Mode Selector Switch) to ‘ Manual’.

14.1.8 In ‘Manual’ mode the Generator operation can be controlled by

operating ‘Manual Excitation’ control switch.

NOTE: In ‘Manual mode, the hand of the Null Balance Meter will not

be at the center.

14.1.9 Procedures to transfer ‘Manual’ to ‘Auto’ are as follows:

Push hold button YA operate SW4 (Auto Excitation Switch) to change

MAVR output till the Null Balance Meter AT ZERO, TURN sw1 TO

‘Auto’. Then release button YA.

14.2 FIELD SUPPRESSION

14.2.1 When the Generator is not running properly, output relay on the

Generator panel will operate and ECC contactor trips to suppress the


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magnetic field of the Generator automatically.

14.2.2 Two ways can be followed to suppress the field for Generator running

in parallel:

1) When the P.F. control is selected and before the Generator is cut off

from grid, energize Auxiliary ZJ2 relay to close the N/O contactors

connected between the multi core 2/3 and 2/5 .In about 30 seconds

M.A.V.R will reduce Generator VAR to 0 automatically. Then the

Generator can be cut off from grid automatically. Switch off SW3

for field- suppression.

2) Manually adjust voltage setting potentiometer (MVSR) or ‘Manual

Excitation’ control switch SW2 to reduce VAR to 0 (the active

power should be 0 preferably). Then open the Main Breaker to cut

the Generator off the grid. Switch off the SW3 for field suppression.

14.2.3 For single running Generator, switch off SW3 for field suppression,

when the Generator has been unloaded.

14.2.4 After field suppression, the Motorize Voltage Setting Potentiometer

(MVSR) should be turn to zero position (i.e. at 12 o’clock position) to

prepare for the next starting.


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