basic of generator

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Generator Basics

GENERATOR BASICS

Generator Basics

• Generator is a machine which converts

Mechanical energy to Electrical energy

• Magnetic Induction Principle

• An emf is induced in a coil whenever

a) a coil cuts through a magnetic field

b) a magnetic field cuts through a coil

Generator Structure

Generator Basics

• emf induction is due to relative motion

between two parts ( coil & magnetic field)

• Relative motion is by Rotation

• Two mechanical parts :

Field - Part which produces magnetism (Rotor)

Armature – part where emf is induced (Stator)

Generator Structure

Generator BasicsGenerator Structure

Generator Basics

• Prime Mover

• Rotor (Exciter)

• Stator

Generator components

Generator Basics

• Source of mechanical power for

relative motion

• Two classes of Prime movers :

High Speed : Steam & Gas Turbines

Low Speed : IC engines, Water turbines and

DC motors

Generator components- Prime mover

Generator Basics

• Type of prime mover plays an important role

in a generator installation

Many characteristics of alternator

and its construction depend upon

Speed at which the rotor is turned.

Generator components- Prime mover

Generator Basics

• Two types are used in rotating field alternators

- Turbine driven rotor

( used where prime mover is a high speed turbine)

- salient pole rotor

( used with low speed prime movers)

Generator components- Rotors

Generator BasicsGenerator components- Rotors

Generator Basics

• Many types based on

- Power out put

- Voltage output

- Type of cooling

- Number of phases

Generator components- Stators

Generator BasicsGenerator components-

Simplified schematic of 3 ph. Stator

• Three single phase windings

displaced by 120 degrees

• Star or Delta connection

• Neutral may or may not be

brought out

• No. of terminals can be

3,4, or 6

Generator Basics

Out-puts from a Generator

Three phase ac power at :

-Rated Voltage

-Rated Frequency

Generator Basics

Out-puts from a Generator – Common Ratings

Small Generators : 25 kVA to 300 kVA

Medium Size Generators : 500 kVA to 1 MVA

Large size Generators : 1 MVA to 25 MVA

Power Plant Generators: 110 MW to 500 MW

Generator Basics

Out-puts from a Generator - Frequency

• Frequency depends up on the

Speed of Rotation ( direct proportion)

• F = PN / 120 where

F = frequency in Hz

P = No. of poles

N = speed of rotation in RPM

( 120 is a constant to convert minutes to seconds

and poles to pole pairs)

Generator Basics

Out-puts from a Generator - Frequency

• Nominal frequency = 50 Hz

• Generator frequency can vary due to

load fluctuations

• Frequency Regulation is mainly

by adjusting the speed

• speed is controlled by varying the fuel

input to the prime mover ( Governor control)

Generator Basics

Out-puts from a Generator - Governors

• Governor ensures frequency at a set value

by increasing / decreasing the fuel input

Generator Basics

Out-puts from a Generator - Governors

Two types of Governors :

Pneumatic : Fuel flow is controlled by

valve position control

Control Input : DC Voltage

Electronic : Fuel flow is controlled by

a total servo mechanism

Control input : DC Voltage pulses

Generator Basics

Droop Characteristics of Governors

Generator Basics

Out-puts from a Generator - Voltage

• Voltage is induced in the stator winding

• Terminal voltage depends upon :

1) No. of conductors in series per winding

2) Speed at which magnetic field cuts the winding

3) Strength of the magnetic field

Generator Basics

Out-puts from a Generator – Voltage Control

• Nominal Voltage = 415 V, 11 kV

• Voltage can vary due to load fluctuations

• Terminal voltage is controlled by

varying the Strength of magnetic field

= varying the current through the field coil

= varying the voltage applied to the field coil

(Exciter control)

Generator BasicsTypical Exciter

Generator Basics

Out-puts from a Generator – Exciters

External to Exciter Transformer

Generator Rectifier Unit

Controls

Built on the Small DC machine

Generator attached to same shaft

of generator

Generator Basics

Typical Exciter

Generator Basics

Neutral terminal

• Very important from the point of view of

a) reducing the fault currents

b) providing effective protection

• should be used for medium size and above

Generator Basics

Neutral Grounding Resistors

Protect generators from excessive fault currents

Provides safety for operators

Provides protection for connected equipment

Generator Basics

Generator Impedance

Synchronous Reactance

Transient reactance

GENERATOR PROTECTION

ϕϕϕϕ = 0o (360O) FORWARD RESISTIVE

ϕϕϕϕ = +30o FORWARD RESISTIVE + FORWARD CAPACITIVE

ϕϕϕϕ = +90o FORWARD CAPACITIVE (LOSS OF FIELD)

ϕϕϕϕ = +120o REVERSE RESISTIVE + FORWADRD CAPACITIVE

ϕϕϕϕ = +150o REVERSE RESISTIVE + FORWARD CAPACITIVE

ϕϕϕϕ = +180o REVERSE RESISTIVE

ϕϕϕϕ = +210o (-150O) REVERSE RESISTIVE + FORWARD INDUCTIVE

ϕϕϕϕ = +270o (-90O) FORWARD INDUCTIVE

ϕϕϕϕ = +300o (-60O) FORWARD INDUCTIVE + FORWARD RESISTIVE

Generator Basics

Generator Behaviour

Influence of Rotor on Stator

Influence of Stator on Rotor

Effect of Load on Generator

Effect of excitation on Generator Impedance

Influence of generator on prime mover

Generator Basics

Generator Behaviour

Influence of Rotor on Stator

• Only variable is excitation current

• Terminal voltage is proportional to

Excitation current

• Will influence Generator impedance

Generator Basics

Generator Behaviour

Influence of Stator on Rotor

• Only variable is the load

• Unbalance loads can cause rotor heating

• Excessive loads can cause out of step

Generator Basics

Generator Behaviour

Effect of Load on Generator

• Load will decide the pF of generator

• Over loads can cause speed reduction

• Unbalance loads can cause over heating

Generator Basics

Generator Behaviour

Effect of excitation on Generator Impedance

Generator Basics

Power output from Generator

Active power kW Controlled by Governor

Reactive Power kVA Controlled by Exciter

� TURBO GENERATOR

� DIESEL GENERATOR

� HYDRO GENERATOR

� WIND GENERATOR

TYPES OF GENERATORS

SUB SYSTEMS OF GENERATORS

� PRIME MOVER

� EXCITATION SYSTEM

� VOLTAGE REGULATOR

� GOVERNOR

� COOLING SYSTEM

FAULTS IN GENERATOR

� EXTERNAL FAULTS

� INTERNAL FAULTS

� ROTOR EARTH FAULT

� FAULTS RELATED TO SUB SYSTEMS

EXTERNAL FAULTS

OVER LOADING

UNBALANCE LOADING

SHORT CIRCUIT

EARTH FAULT

INTERNAL FAULTS

� PHASE TO PHASE FAULTS IN WINDINGS

� PHASE TO EARTH FAULTS

ROTOR EARTH FAULT

� DOUBLE EARTH FAULT TRIPPING

FAULTS RELATED TO SUB-SYSTEMS

� UNDER VOLTAGE

� OVER VOLTAGE

� UNDER FREQUENCY

� OVER FREQUENCY

� REVERSE POWER

� LOSS OF EXCITATION

� LOW-FORWARD POWER

TYPES OF FAULTS (STATOR SIDE)

VOLTAGE RESTRAINED OVER CURRENT

THERMAL OVER LOAD

CURRENT UNBALANCE

OVER VOLTAGE

UNDER VOLTAGE

OVER FREQUENCY

UNDER FREQUENCY

LOSS OF FIELD

REVERSE POWER

UNDER POWER

OUT OF STEP

INADVERTANT ENERGISATION

EARTH FAULT (100%)

EARTH FAULT (95%)

GENERATOR DIFFERENTIAL

OVER EXCITATION (V/Hz)

TYPES OF FAULTS (ROTOR SIDE)

ROTOR EARTH FAULT

EXCITATION UNDER VOLTAGE

EXCITATION UNDER CURRENT

DIODE FAILURE

SINGLE LINE DIAGRAM

49 46 40

51V 37 64

6.6 MW

11000/110v

VOLTAGE RESTRAINED OVER CURRENTVOLTAGE RESTRAINED OVER CURRENT

- WHEN O/C FAULT, TERMINAL VOLTAGE REDUCES.

- RELAY MAY NOT TRIP, SINCE FAULT CURRENT

THROUGH RELAY MAY BE LESS THAN SET POINT

NECESSARY TO VARY THE O/C PICK UP SETTING

WITH RESPECT TO VOLTAGE

VOLTAGE RESTRAINED OVER CURRENTVOLTAGE RESTRAINED OVER CURRENT

I*/ [I>]

0.2 0.8

LOSS OF FIELD IN GENERATORS

GENERATOR WILL OVER SPEED &

OPERATE AS AN INDUCTION GENERATOR

(OVER SPEEDS OF THE ORDER OF 2 TO 5% )

GENERATOR WILL CONTINUE TO DELIVER POWER

WILL DERIVE EXCITATION FROM THE SYSTEM

STATOR CURRENT WILL BE 200%

THERE WILL BE HEAVY ROTOR CURRENT

RESULTS IN OVER HEATING

PHASE ANGLE BETWEEN

ANGLE ϕϕϕϕ VOLTAGE & CURRENT

IMPEDANCE REPLICA OF

ANGLE αααα PHASE ANGLE

αααα = 360O - ϕϕϕϕ

ααααϕϕϕϕ

ϕϕϕϕ = 0o (360O) FORWARD RESISTIVE

ϕϕϕϕ = +90o FORWARD CAPACITIVE (LOSS OF FIELD)

ϕϕϕϕ = +120o REVERSE RESISTIVE + FORWADRD CAPACITIVE

ϕϕϕϕ = +150o REVERSE RESISTIVE + FORWARD CAPACITIVE

ϕϕϕϕ = +180o REVERSE RESISTIVE

ϕϕϕϕ = +270o (-90O) FORWARD INDUCTIVE

LOSS OF

NORMAL

LOSS OF FIELD

PROTECTION

LOSS OF

NORMAL

LOSS OF FIELD

PROTECTION

REVERSE POWER GENERATORS

GENERATOR WILL BECOME MOTOR

HARMFUL TO THE PRIME MOVER

( STEAM TURBINE WILL OVER HEAT)

(DIESEL ENGINE WILL EXPLODE DUE

TO UNBURNT FUEL)

(HYDRAULIC TUBINE WILL HAVE CAVITATION)

STATOR EARTH FAULT

95% EARTH FAULT NORMAL RELAY

100% EARTH FAULT SPECIAL RELAY

SENSES ABSENCE

OF 3RD HARMONICS

STATOR EARTH FAULT0 %

95%95 TO 100%

INADVERTANT ENERGISATION

- APPLICATION OF FULL VOLTAGE AT

STANDSTILL

COASTING TO STOP

BEFORE SYNCHRONISM

- PRESENCE OF UNBALANCE VOLTAGE DUE TO

FLASH OVER AT IONE OR TWO POLES OF BREAKER

GENERATOR FORCED TO START AS

INDUCTION MOTOR RESULTING IN MECHANICAL

DAMAGES TO PRIME MOVER AND EXCESSIVE

HEATING IN THE ROTOR

V/Hz PROTECTION

- INCORRECT VOLTAGE REGULATOR ACTION

- LOAD THROW - OFF

- SUDDEN OVER VOLTAGE / OVER FREQUENCY

RESULTS IN OVER FLUXING OF GENERATOR

AND OVER HEATING

rrrr rrrr

rrrrrrrr rrrr

BC1 BC2

B1 B2 B3

G1 G2 G3

PT1 PT2 PT3

CT1 CT2 CT3

BUS-1 BUS-2 BUS-3

PULSES FOR

GOVERNOR &

EXCITER

PULSES FOR

GOVERNOR &

EXCITER

PULSES FOR

GOVERNOR &

EXCITER

LOAD SHARING OF GENERATORS

LSR = LOAD SHARING RELAY

Fig. -1

GRID ISLANDING SCHEME

REVERSE POWER RELAY

LOW FORWARD POWER RELAY

UNDER VOLTAGE RELAY

DIRECTIONAL O/C + E/F RELAY

dF/dT RELAY

UNDER FREQ. RELAY

OVER FREQ. RELAY

VECTOR SURGE RELAY

GRID INCOMER

TRANSFORMER

rrrrrrrrrrrr

Fig. -2

SYNCHRONISATION OF GENERATORS

SYNCHRONISING IS THE PROCESS OF

ELECTRICALLY CONNECTING

TWO AC POWER SOURCES WITH

ROTATING MACHINES

WITHOUT ANY DISTURBANCE TO

EXISTING SYSTEM AND

WITHOUT ANY DAMAGE TO THE

EXISTING SYSTEM

SYNCHRONISATION

SINGLE GENERATOR TO A BUS

(DEAD BUS / LIVE BUS SYNCH.)

MULTIPLE GENERATORS TO A BUS

(SIZE, VINTAGE, RESPONSE TIMES)

AUTO CHANGEOVER IN BUS CONNECTIONS

MANUAL & AUTO SYNCHRONISATION

REVERSE SYNCHRONISATION

PARAMETERS GOVERNING

SYNCHRONISATION :

VOLTAGE

FREQUENCY

PHASE ANGLE

rrrrrrrr B1 B2

PT1 PT2

COMMON BUS

SYNCHRONISING OF GENERATORS

SCM 21

RESULTS OF INCORRECT SYNCHRONISATION

FREQUENCY ACTIVE POWER FLOW

HIGH FREQ. TO LOW FREQ.

PHASE ANGLE JOLT TO THE SYSTEM

FATIGUE TO SHAFT

DAMAGE TO BEARINGS

OVER HEATING OF STATOR

VOLTAGE REACIVE POWER FLOW

HIGH VOLTAGE TO LOW VOLTAGE

GRID INCOMER

TRANSFORMER

rrrrrrrrrrrr

GENERATORS IN PARALLEL

TYPES OF PARALLEL OPERATION

�MULTIPLE GENERATORS ON A COMMON BUS

WITHOUT CONNECTION TO GRID

�GENERATORS CONNENCTED TO GRID IN

IMPORT ONLY MODE

�GENERATORS CONNECTED TO GRID IN

IMPORT + EXPORT MODE

ISSUES TO BE ADDRESSED

BASIC PROTECTIONS

•SEQUENTIAL STARTING & SYNCHRONISATION

•NEUTRAL SWITCHING LOGIC

• INSTABILITY & HUNTING AT HIGHER POWER O/P

•CASCADED TRIPPING ON LOAD FLUCTUATION

•REVERSE POWER FLOW DUE TO BREAKER FAILURE

•POOR POWER FACTOR

•EFFECT OF GRID DISTURBANCES &

GRID ISLANDING SCHEMES

•LOAD MANAGEMENT AFTER ISLANDING

•REVERSE SYNCHRONISATION

BASIC PROTECTIONS

OVER CURRENT + E/F

THERMAL OVER LOAD

UNDER VOLTAGE + OVER VOLTAGE

UNDER FREQUENCY + OVER FREQUENCY

LOSS OF FIELD

CURRENT UNBALANCE

REVERSE POWER

DIFFERENTIAL + REF

ROTOR E/F

SEQUENTIAL STARTING & SYNCHRONISATION

AMF SCHEME

STARTING LOGIC

AUTO SYNCHRONISATION

- DEAD BUS SYNCHRONISATION (FIRST MACHINE)

STARTING/ STOPPING OF GENERATOR NEXT IN LINE

- LIVE BUS SYNCHRONISATION

(SUBSEQUENT MACHINES)

PT SWITCHING LOGIC

SEQUENTIAL STARTING & SYNCHRONISATION

MAINS FAILURE

DETECTION

I/C TRIP &

STARTING LOGIC

3 ATTEMPT

STARTERS

PT SWITCHING

AUTO SYNCH. OF

GENERATORS

CUT IN – CUT OUT

NEUTRAL SWITCHING LOGIC

MASTER GENERATOR NEUTRAL TO BE GROUNDED

INSTABILITY AT HIGHER O/P & CASCADED TRIPPING

ERRATIC RESPONSE TO LOAD FLUCTUATIONS

- DIFFERENT SIZES OF GENERATORS

- DIFFERENT VINTAGES OF GENERATORS

IMROPER LOAD ALLOCATION TO

EACH GENERATOR

OPERATOR’S LIMITATIONS

rrrr rrrr

rrrrrrrr rrrr

BC1 BC2

B1 B2 B3

G1 G2 G3

PT1 PT2 PT3

CT1 CT2 CT3

BUS-1 BUS-2 BUS-3

PULSES FOR

GOVERNOR &

EXCITER

PULSES FOR

GOVERNOR &

EXCITER

PULSES FOR

GOVERNOR &

EXCITER

GENERATORS ON COMMON BUS – AUTO LOAD SHARING SCHEME

LSR = LOAD SHARING RELAY RRS

Fig. -1

REVERSE POWER FLOW

rrrrrrrr

PT1 PT2

CT1 CT2

BUS-1 BUS-2

Fig. -2

G1 STOPS DUE TO

MECHANICAL PROBLEMS

B1 WILL NOT TRIP

G2 WILL FEED G1

POOR POWER FACTOR

PULSES FOR

GOVERNOR &

EXCITER

LSR = LOAD SHARING RELAY

REFERENCE

VOLTAGE

SOURCE

KEEP RATIO OF

KW/KVAr CONSTANT

Fig. -3

HANDLING OF GRID DISTURBANCES

� GRID FAILURE

� GRID FAULT

� OVER LOAD IN THE GRID

� UNDER / OVER VOLTAGE IN THE GRID

GRID ISLANDING SCHEME

REVERSE POWER RELAY

LOW FORWARD POWER RELAY

UNDER VOLTAGE RELAY

DIRECTIONAL O/C + E/F RELAY

dF/dT RELAY

UNDER FREQ. RELAY

OVER FREQ. RELAY

VECTOR SURGE RELAY

GRID INCOMER

TRANSFORMER

rrrrrrrrrrrr

LOAD MANAGEMENT AFTER ISLANDING

� LOAD SHEDDING- FREQUENCY BASED

- POWER BASED

� LOAD SHADING

� AUTO SYNCHRONISING

� LOCATION OF SYNCHRONISING

THANK YOU

basic of generator

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