excitation system on power system stability

7/22/2019 Excitation System on Power System Stability

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Impact of excitation system on power system stability

ABB Industrie AG

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ABB

1. INTRODUCTION


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ABB Industrie AG

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ABB

THE POWER STATION

GOVERNOR

AC & DC

AUXILIARY

SYSTEMS

PROTECTION

PTs

&

CTs

LV SWITCHGEAR

GENERATORBREAKER

STEP UP

TRANSFORMER

HV- BREAKER

HV SYSTEM

CONTROL ROOM

1

1

CONTROL

SYSTEMS

EXCITATIO

NSYSTEM

AUX.

TRANSF

.

SYNCHRONOUSGENERATOR

STAR

POINT

CUBICLE

TURBINE

EXCITATION

TRANSFORMER

SYNCHRONIZING


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ABB Industrie AG

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ABB

The automatic voltage control system

SynchronousMachine

ExcitationSystem

GridIf Ug

Controller


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ABB Industrie AG

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ABB

~=

SM E

1 a 200 A

Rotating exciter

~=SM

100 a 10000 A

Static excitation


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ABB Industrie AG

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ABB

Basic Requirements

Excitation Current up to 10000 amps

Input frequency range from 16 Hz to 400 Hz Adaptable to different redundancy requirements for controls and

converters

State of the art man machine interface

Compatibility with most applied power plant control systems Remote diagnostics

Comfortable commissioning tools


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ABB Industrie AG

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ABB

Operational Application


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ABB Industrie AG

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ABB

Main Components of an UNITROL 5000 System

AVR


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ABB Industrie AG

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ABB

System overview

Me

asuring

Protection

Monitoring

AVR + FCR

Logic Control

FieldbreakerField flashing

Field suppression

AVR 1

AVR 2

Converter

Control

CONVERTER 1

CONVERTER 2

CONVERTER N

AVR = Autom. Voltage Reg.

FCR = Field Current Reg.


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ABB Industrie AG

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ABB

Main Functions of the AVRwith Field Current Controller

+

_

+

_

AVR Setpoint-V/Hz limiter

- Soft start- IQ Compensation

- IP Compensation

Underexcit. limiter-Q=F(P,U,UG)

-Stator current lead

-Min. field current

Overexcit. limiter-Max field current

-Stator current lag

Power SystemStabilizer PSS

Man setpoint

MeasuringandA/Dc

onversion

Min.

/max.valuepriority

PID

PI

To pulse

generation

UG, IG, If

UG, IG

UG

UG, IG, If

UG, IG

If


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ABB Industrie AG

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ABB

2. IMPACT ON POWER SYSTEM STABILITY

Voltage Control Dynamics ( controller, power stage and power source)

Limiters

Power System Stabilizer


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ABB Industrie AG

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ABB

2.1 Voltage Control Dynamics ( controller, power stage and power source)


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ABB Industrie AG

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ABB

Computer representation of the AVR

Parameter Description Unit Range

TR Measuring filter time constant s 0.020

Ts Gate control unit and converter time constant s 0.004

KIR Reactive power compensation factor p.u. -0.20...+0.2

KIA active power compensation factor p.u. -0.20...+0.2

KR Steady state gain p.u. 10...1000

Kc Voltage drop to commutations andimpedances

p.u. Acc. Transf.

TB1 Controller first lag time constant s TB1

TB2TB2 Controller second lag time constant s 0


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ABB Industrie AG

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ABB

Synchronous machine

three-phase representation

URIR

US

IS

UT

IT

UfIf

IDR

IDT

IDS


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ABB Industrie AG

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ABBd-q decomposition

UdId

Uf If

IdD

Uq

Iq

IQ2

IQ1

d

f

q

dD

Q1 Q2

D axis

Q axis

ra

ra

rdD

rf

rQ1 rQ2

Rotor

Stator


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ABB Industrie AG

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ABB

TMPM

speed

TE US EpXq XT XE

=

= + +sin

Motion equation:

TM TE Hd

dt = 2

45o0o

TM

Torque

180o

The characteristic Dynamic Equation


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ABB Industrie AG

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ABB

AVR - Voltage control dynamic

Response time

Ceiling capabilities

Settings of control algorithm

Excitation system nominalresponse

IEEE 421.1

System type (Static excitation, Brush-less, DC Exciter)

UF ceiling

e=0.5so

a

b

d

c

UF nominal

NR=ce-ao

(ao)(oe)


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ABB Industrie AG

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ABB

Comparison of Excitation System Types

Mechanical

-Conversion ofmech. to electr.

Energy

- Size of exciter

- Sliprings

Electrical

- Rectifier

- Direct

measuring

of field current

- Fast field

suppression

DC-Exciter

yes

power and speed

yes

not required

possible

possible

AC-Exciter

stat. diodes

yes

power and speed

yes

static external

possible

possible

AC-Exciter

rot. diodes

yes

power and speed

no

static rotary

not possible

not possible

Stat. Exciter

stat. thyristors

main machine

power

yes

static

possible

possible


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ABB Industrie AG

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ABB

Comparison of Exciter Characteristics

Dynamic

Performance

- Major time

constant of control circuit

- Ceiling factor

- Negative field

current

Reliability (MTBF)

- Machine, Transformer

- Converter

Maintenance

- Machine, Transf.

- Converter

DC-Exciter

TdL+TE

limited

possible

good

good

at standstill

at standstill

AC-Exciter

stat. diodes

TdL+TE

not limited

not possible

good

better

at standstill

during

operation

AC-Exciter

rot. diodes

TdL+TE

limited

not possible

good

better

at standstill

at standstill

Stat. Exciter

stat. thyristors

TdL

not limited

possible

better

better

at standstill

during

operation


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ABB Industrie AG

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ABB

Ceiling limit


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ABB Industrie AG

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ABB

2.2 LIMITERS


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ABB Industrie AG

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ABB

Transducer

and filter

-Setpoint

-Soft start

-V/Hz limiter

-Q influence

-P influence

HV

Gate

LV

Gate

Power system

stabilizer

(PSS)

Under excitationlimiters (UEL)

Ug actual

effective setpoint

UgAC

Setpoint buildingAutomatic

channel

Over excitation

limiters (OEL)

DC

Gain

P gain

HF gain

1/TA 1/TB

Gain

Ucmin

Ucmax

+

+

+

DC

Gain

P gain

1/TA 1/TB

Gain

Ucmin

Ucmax

Transducer

and filter

IF

+

-

+

-

Manual set point

Follow up

control

Uc

Follow up Manual

Follow up

Automatic

Uc AVR

Uc FCR

Follow up

Automatic

Uc FCR

Uc AVR

+

FCR

AVR


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ABB Industrie AG

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ABB

The Power Chart of a solid polesynchronous machine

LAGGING(overexcited)

LEADING(underexcited)

Xd

U2

Xq

U2 1.0-1.0 p.u. Q [p.u.]

P [p.u.]

Thermal limit of

stator

Thermal limit

of rotor

n

Rate

da

ppa

rent

powerS

n

Theorectical

stability limit

Practical stability

limit

Turbine ouput

power limit

Excita

tionpo

wer

IF

Declared rated

operation point of

generating unit

Minimum Field

current limit

Safe operation range


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ABB Industrie AG

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ABB

Synchronous machine operation Limits

Max. field current limiterMax. field current limiter

Min. field current limiterMin. field current limiter

Stator current limiterStator current limiter

Under excitation P,Q limiterUnder excitation P,Q limiterP

+Q-Q 1/Xd

Theoreticalstability limit


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ABB Industrie AG

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ABB

Main duty of the limiters:

Keep the synchronous machine operating withinthe safe and stable operation limits, avoidingthe action of protection devices that may trip

the unit.


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ABB Industrie AG

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ABB

VOLTAGE REGULATOR WITH LIMITERS


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ABB Industrie AG

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ABB

~

=

SM=

Voltagesetpoint

=

= / ~

Supply

~

Ifth setpoint

Ifact-+ I dt2 COMPU

/ #

I dt2 maxIfmax

LOWERV

AL.GATE

-

+

+-

THE OPERATING PHILOSOPHY OF Ifmax LIMITER


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ABB Industrie AG

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ABB

FieldcurrentxIFN

Time [s]

thermal limit

Ceiling limit

setpointswitch time


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ABB Industrie AG

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ABB

2.3 Power system Stabilizer


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ABB Industrie AG

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ABB

Ep

Xq(s)

Infinite

Bus

XEXT

UG

XT+XE

US

I

X q s X qs T q

s T q o '

s T q

s T q o '( )

' ' '

'= ++

++

1

1

1

1

Stationary and transient air gap voltages

Ep-S

Ep

Ep

UG

US

=I.Xq

= I. (XE+XT)

= I. Xq

H


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ABB Industrie AG

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ABB

US

UGEp

PE

phasorrotation

Transient behavior of and PE

90o

Pe


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ABB Industrie AG

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ABBDynamic equation of synchronousmachine+grid for small oscillations

XT+XE

Infinite BusHA)

B)

XT+XE

H1 H2 Equivalent Inertia HeqH H

H H= +

1 2

1 2

For small oscillations keeping the drivingtorque constant the dynamic equationlinearized can be written as:

TM TE Hd

dt

= 2 taking TM TE H

d

dt

= 22

2

21 0

2

2

+ + =Hn

d

dt

D

n

d

dtK

Dampingtorque

SynchronizingTorque

Inertia. Ang. Acc.

3 3


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K n

H

1

2

Oscillation frequency

rad/s

90o0o

Torque

operating point

K slopeT Ep Us

Xq' XE XTo1 = = = + +

'.cos '

K1=synchronizing coefficient

o

Phasor diagram of machine+grid

for small oscillations ( without AVR)

D/ws*

phasor rotation

Te=K1.

UG Positive Damping(Stable Region)

Negative Damping(Unstable Region)

Synchronizing Axis

Damping axis

ResultingTorque

3 4


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ABB Industrie AG

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ABB

21 0

2

2

+ + + =Hn

d

dt

D

n

d

dtK K2 Ep

'

Damping

torque

Synchron.

Torque

Inertia.Ang. Acc. Add .Torque

from exc. system

K2.Ep

Phasor diagram of machine+grid+excitation system

for small oscillations

D/ws*phasor rotation

Te=K1.

UGPositive Damping

(Stable Region)

Negative Damping(Unstable Region)

Synchronizing Axis

-UG

Resulting torque componentwithout excitation system

Resulting torque componentwith excitation system

3 5


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ABB Industrie AG

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ABB

P,Q

M

UG

ALTERNATIVE

FINALCTRLELEMENT

~

AVR PSS

Fig3: PSS in the excitation system

3 6


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ABB Industrie AG

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ABB

Main Target of PSS:

It provides an additional torque component in order to get:

1) A positive resulting torque component on damping axis, even for thehighest possible rotor oscillation frequency.

2) A positive torque component on synchronizing axis for partialcompensation of generator terminal voltage variations even forthe highest possible oscillation frequency

3 7


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ABB

PSS2A acc. IEEE 421.5 1992

PE

+

s.TW1

1 + s.TW1

s.TW3

1 + s.TW3

PM1 + s.2.H

Ks2

1 + s.T7

s.TW2

1 + s.TW2

s.TW4

1 + s.TW4

( )

( )

1 8

1 9

+ +

s T

s T M

N

Ks3

++

-

1+s.T1

1+s.T2Ks1

1+s.T3

1+s.T4

VST

VSTmax VSTmax

VSTmin VSTmin

PE1 + s.2.H

PA1 + s.2.H

- 3 8 -


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ABB

Adaptive PSS (APSS) Alternative to PSS2A

AVR

Synchronous

Generator

Uf

Driving Power Pa

Measurement

Filter

PUG

UG , IG

APSS

PEstimator

3rd Order System Model

RegulatorWhite

noise

+

+ -

+

+

Uref +

+

GRID

- 3 9 -


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ABB Industrie AG

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ABB

Output

Limit To

AVR

FB1(s)

FB2(s)

FI1(s)

FI2(s)

FH1

(s)

FH2(s)

K b

K i

K h

+

-

-

-

+

+

+

+

Multi Band PSS (MBPSS)

excitation system on power system stability

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