WHAT IS EXCITATION?

IT IS THE REACTIVE POWER

REQUIRED BY A

SYNCHRONOUS MACHINE

FOR ITS OPERATION

IT IS THE ARRANGEMENT

THROUGH WHICH THE

REACTIVE POWER TO THE

GENERATOR IS SUPPLIED

WHEN IT IS CONNECTED

WITH THE GRID.

EXCITATION SYSTEM RESPONSE

RELIABILITY

STABILITY

QUICK RESPONSE

EXCITATION SYSTEM RESPONSE

RESPONSE RATIO

CEILING VOLTAGE

STEADY STATE AND TRANSIENT

STABILITY

EXCITATION SYSTEM RESPONSE

RESPONSE RATIO= RATE OF RISE OF

EXCITATION VOLTAGE(V/S)/NOMINAL

VOLTAGE

GENERALLY CALCULATED FOR .5S AND

COMES TO 2x MAXIMUM VOLTAGE

APPLIED/RATED VOLTAGE

voltage

A

time O

D

C

B

Actual build up of

voltage

.5 S

EXCITATION SYSTEM RESPONSE

CEILING VOLTAGE

IT IS THE MAXIMUM VOLTAGE APPLIED

ACROSS THE FIELD WINDING FOR VERY

SHORT DURATION (APPX. 10S) AND

GENERALLY 1.5 TO 2 TIMES OF RATED

VOLTAGE.

EXCITATION SYSTEM RESPONSE

STEADY STATE STABILITY CAPACITY OF THE MACHINE TO PRODUCE FORCE EQUAL TO

DISTURBING FORCES SO THAT SYNCHRONISM COULD BE

MAINTAINED.

P

O

W

E

R

LOAD ANGLE

90

EXCITATION SYSTEM RESPONSE

TRANSIENT STABILITY

P

O

W

E

R

LOAD ANGLE

TYPES OF EXCITATION

DC EXCITATION SYSTEM USING DC EXCITER

AND VOLTAGE REGULATOR

AC EXCITATION SYSTEM USING PILOT

EXCITOR AND DC CONTROLLER

BRUSHLESS EXCITATION SYSTEM

STATIC EXCITATION SYSTEM

DC EXCITATION USING DC EXCITOR AND

VOLTAGE REGULATOR THE EXCITATION SUPPLY IS TAKEN FROM

STATION DC AND FED TO INDIVIDUAL MACHINE THROUGH RHEOSTAT.

THE RHEOSTAT IS CONNECTED IN SERIES WITH FIELD WINDING OF THE MACHINE.

THE TERMINAL VOLTAGE IS ADJUSTED USING THIS RHEOSTAT.

SUITABLE FOR LOW CAPACITY MACHINE.

AC EXCITATION SYSTEM

A SHAFT DRIVEN AC PILOT EXCITOR HAVING ROTATING FIELD AND STATIONARY ARMATURE.

THE AC OUT OF PILOT EXCITOR IS FED STATIONARY DIODE THROUGH CONTROLLED RECTIFIER.

THE STATIONARY DIODES OUTPUT DC IS FED TO GENERATOR FIELD THROUGH SLIP RINGS.

BRUSHLESS SYSTEM

DIODE RECTIFIERS ARE MOUNTED ON THE GENERATOR

SHAFT.

RECTIFIER OUTPUT IS DIRECTLY FED TO GENERATOR

FIELD.

THIS AVOIDS SLIP RING AND CARBON BRUSH

ARRANGEMENT.

STATIC EXCITATION SYSTEM

THE AC POWER IS TAPPED OFF FROM GENERATOR TERMINALS.

STEPPED DOWN BY RECTIFIER TRANSFORMER.

RECTIFIED BY FULLY CONTROLLED THYRISTOR BRIDGE.

FED TO GENERATOR TERMINALS BY SLIP RING AND CARBON BRUSH ASSEMBLY.

THE GENERATOR FIELD INPUT CONTROLS THE GENERATOR OUTPUT VOLTAGE.

Automatic voltage

regulator

Rotor angle limiter

Slip stabilizer

Regulator Power supply

Filter

Grid control

Grid control

Pulse amplifier

Pulse amplifier

Pulse supervision

X-mer prot >1

X-mer prot >1

Pulse final Stage

Gate ckt

Stator current limiter

Rotor current limiter

M

M Auto/Man

DC source

o/ v prot

Fan supply

Rectifier

transformer

Comparator& Follow up

Auto channel

Manual channel

G Field breaker

AC source

Field flashing

STATIC EXCITATION SYS: BLOCK DIAGRAM

PT

CT

Filter

575/380

575/380

THYRISTOR

15.75kv/575

PARTS OF STATIC EXCITATION SYSTEM

RECTIFIER TRANSFORMER

SCR OUTPUT STAGE

EXCITATION START UP AND FIELD DISCHARGE

EQUIPMENT

REGULATOR AND OPERATIONAL CONTROL

CIRCUITS.

RECTIFIER TRANSFORMER

THIS IS RESIN CAST COIL, DRY TYPE X-MER WITH

NATURAL/ FORCED AIR COOLING.

15.75/0.580 KV, DYn5 TRANSFORMER.

PRIMARY IS CONNECTED WITH GENERATOR OUT PUT.

SECONDARY IS FEEDING TO 580V 3-PHASE AC BUS

FEEDING TO SCR BRIDGES THROUH FUSES.

SCR OUTPUT STAGE

CONSISTS OF SUITABLE NO OF BRIDGES CONNECTED IN

PARALLEL.

EACH BRIDGE COMPRISES OF SIX THYRISTORS WORKING

AS SIX PULSE FULLY CONTROLLED BRIDGE.

CURRENT CARRYING CAPACITY OF EACH BRIDGE

DEPENDS ON THE RATING OF INDIVIDUAL THYRISTOR.

BY CHANGING FIRING ANGLE, VARIABLE OUTPUT IS

OBTAINED.

SCR OUTPUT STAGE

EACH BRIDGE IS CONTROLLED BY ONE FINAL PULSE

STAGE AND COOLED BY FAN.

N-1 BRIDGE OPERATION IS ENSURED.

FAILURE OF TWO BRIDGES LIMITS THE EXCITATION

CURRENT.

FAILURE OF THREE BRIDGES ENSURES GENERATOR

TRIPPING.

SHUNT CIRCUIT

THIS TAPS THE POWER FROM GENERATOR TERMINALS AND FEEDS DC POWER TO SLIP RINGS THROUGH FIELD BREAKER.

FOR INITIAL EXCITATION, A SEPARATE SUPPLY SOURCE IS REQUIRED AS THE REMANENCE VOLTAGE OF GENERATOR IS TOO LOW.

THIS SOURCE GETS DISCONNECTED AUTOMATICALLY WHEN THE THE GENERATOR OUTPUT VOLTAGE REACHES TO 70% OF ITS RATED VALUE.

EXCITATION CURRENT LIMITER

PREVENTS THE THERMAL OVERLOADING OF ROTOR BY

LOWERING THE OUTPUT VALUE OF THE VOLTAGE

REGULATOR AND THUS THE FIELD VOLTAGE.

LOAD ANGLE LIMITER

INCREASES THE FIELD VOLTAGE AND THUS

STOPS THE GENERATOR FROM FALLING OUT

OF STEP.

STATOR CURRENT LIMITOR

THIS REDUCES THE EXCITATION CURRENT WHEN THE

STATOR CURRENT EXCEEDS A SAFE PERMISSIBLE LIMIT

IN INDUCTIVE DIRECTION.

PULSE MONITOR

THIS IS CONNECTED TO THE BUS BAR.

IF FAULTY PULSES OR PULSE FAILURE

ARE DETECTED, THE CHANNEL

CHANGES TO ANOTHER STANDBY

CHANNEL .

PULSE COMPARING STAGE

IT COMPARES PULSE POSITION OF

BOTH CHANNELS.

MATCHING IS AFFECTED WITH FOLLOW-

UP CONTROL DEVICE.

FIELD BKR TRIPPING PROTECTIONS

1.CLASS-A

30Z 86G 386GX FIELD BKR

a. Transformer over current instantaneous

b. Transformer over current delayed protection

c. Rotor over voltage

d. 48V supply fail

e. Three or more failed:

1. Fan failed

2. Pulse final stage power failure

3. Thyristor fuse failed.

4. Isolator open

continue

FIELD BKR TRIPPING PROTECTIONS 2. Class B

30F UTR LFPR(32GI) 86G 386G FB TRIP

Rotor Earth Fault, Stage-2(IR value <2.2k ohm).

Regulator supply fuse fail.

Manual channel fail.

Thyristor supply fail.

Transformer temp HI-HI.

3. Direct trip

Trip the Field Breaker directly, Generator trips through field failure relay

EXCITATION START UP

FIELD FLASHING IS REQUIRED FOR

INITIAL BUILD UP OF GENERATOR

VOLTAGE.

BOTH DC & AC FIELD FLASHING ARE

PROVIDED FOR RELIABILITY.

FIELD DISCHARGE EQUIPMENT

ON TRIPPING OF GENERATOR, ITS

STORED ENERGY IS REQUIRED TO BE

DISCHARGED.

THIS IS DONE THROUGH A NON LINEAR

DISCHGARGE RESISTENCE.

DIGITAL VOLTAGE REGULATOR

THE PRESENT DAY MICROPROCESSOR BASED EXCITATION SYSTEM NOT ONLY MEET THE VOLTAGE REGULATION FUNCTION BUT ALSO PROVIDES ENHANCED INTERNAL CONDITION MONITORING AND EXTENSIVE FAULT DIAGNOSIS BESIDES PROVIDING OPERATING FLEXIBILITY AND OTHER ADVANTAGES ASSOCIATED WITH DIGITAL SYSTEM.

DVR OPERATION

THE DVR PERIODICALLY CALCULATES THE CONTROL SIGNAL FROM THE MEASURED AND REFERANCE VALUES.THE CALCULATION IS REPEATED AT VERY SHORT TIME INTERVALS (= 3.3 ms) RESULTING IN APPARENTLY CONTONUOUS REGULATOR OUTPUT SIGNAL.

DVR FUNCTIONS

CONTROL OF GENERATOR VOLTAGE

LIMITATION OF FIELD CUURENT

LIMITATION OF LOAD ANGLE

LIMITATION OF STATOR CURRENT

SLIP STABILISATION

FORMATION OF GENERATOR VOLTAGE

ACTUAL VALUE SIGNAL

REFERENCE /ACTUAL VALUE DIFFERENCE

PID ALGORATHIM

ADVANTAGES OF DVR

FAST RESPONSE(<20ms) TO NETWORK DISTURBANCES.

SYSTEM REDUNDENCY AT INTERNAL POWER SUPPLY, CONTROLS & EXCITATION POWER OUTPUT.

SELF MONITORING & DIAGNOSTIC FEATURE.

MAINTAINS DRIFT FREE PARAMETERS

AVAILABILITY OF SINGLE/DUAL AUTO CONTROL CHANNEL.

ADVANTAGES OF DVR

FACILITY TO PROVIDE ADOPTIVE TYPE PSS.

LOW FAILURE RATE OF CKT COMPONENTS.

FACILITY TO PROVIDE SECURITY MEASURE FOR UNWANTED OPERATION.

POSSIBILITY OF ON LINE REPAIR.