Download - 94631980 Generator Excitation System
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WHAT IS EXCITATION?
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IT IS THE REACTIVE POWER
REQUIRED BY A
SYNCHRONOUS MACHINE
FOR ITS OPERATION
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IT IS THE ARRANGEMENT
THROUGH WHICH THE
REACTIVE POWER TO THE
GENERATOR IS SUPPLIED
WHEN IT IS CONNECTED
WITH THE GRID.
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EXCITATION SYSTEM RESPONSE
RELIABILITY
STABILITY
QUICK RESPONSE
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EXCITATION SYSTEM RESPONSE
RESPONSE RATIO
CEILING VOLTAGE
STEADY STATE AND TRANSIENT
STABILITY
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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
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voltage
A
time O
D
C
B
Actual build up of
voltage
.5 S
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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.
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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
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EXCITATION SYSTEM RESPONSE
TRANSIENT STABILITY
P
O
W
E
R
LOAD ANGLE
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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
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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.
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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.
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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.
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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.
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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
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PARTS OF STATIC EXCITATION SYSTEM
RECTIFIER TRANSFORMER
SCR OUTPUT STAGE
EXCITATION START UP AND FIELD DISCHARGE
EQUIPMENT
REGULATOR AND OPERATIONAL CONTROL
CIRCUITS.
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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.
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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.
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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.
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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.
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EXCITATION CURRENT LIMITER
PREVENTS THE THERMAL OVERLOADING OF ROTOR BY
LOWERING THE OUTPUT VALUE OF THE VOLTAGE
REGULATOR AND THUS THE FIELD VOLTAGE.
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LOAD ANGLE LIMITER
INCREASES THE FIELD VOLTAGE AND THUS
STOPS THE GENERATOR FROM FALLING OUT
OF STEP.
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STATOR CURRENT LIMITOR
THIS REDUCES THE EXCITATION CURRENT WHEN THE
STATOR CURRENT EXCEEDS A SAFE PERMISSIBLE LIMIT
IN INDUCTIVE DIRECTION.
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PULSE MONITOR
THIS IS CONNECTED TO THE BUS BAR.
IF FAULTY PULSES OR PULSE FAILURE
ARE DETECTED, THE CHANNEL
CHANGES TO ANOTHER STANDBY
CHANNEL .
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PULSE COMPARING STAGE
IT COMPARES PULSE POSITION OF
BOTH CHANNELS.
MATCHING IS AFFECTED WITH FOLLOW-
UP CONTROL DEVICE.
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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
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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
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EXCITATION START UP
FIELD FLASHING IS REQUIRED FOR
INITIAL BUILD UP OF GENERATOR
VOLTAGE.
BOTH DC & AC FIELD FLASHING ARE
PROVIDED FOR RELIABILITY.
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FIELD DISCHARGE EQUIPMENT
ON TRIPPING OF GENERATOR, ITS
STORED ENERGY IS REQUIRED TO BE
DISCHARGED.
THIS IS DONE THROUGH A NON LINEAR
DISCHGARGE RESISTENCE.
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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.
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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.
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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
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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.
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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.