Generator and Excitation Flashcards
What causes Generator Unit Differential (Unit HEA) to roll?
- **Emergency Trip Pushbutton **
- Loss of Stator Cooling Water
- 26KV Bus Duct Ground Fault (Backfeed)
- Generator Differential
- Generator Ground
- Generator Overcurrent During Startup
- Exciter Differential
- Exciter Field Breaker Open
- Main Transformer Differential
- Main Transformer Sudden Pressure
- UAT Differential
- UAT Ground
- UAT Sudden Pressure Trip
What causes the Generator Overall Differential (Overall HEA) to roll?
- Turbine Trip (33VED)
- Breaker Failure Relays (trips other yard bkrs)
- Reverse power (Gen Motoring U1)
What does the Main Exciter do?
Generates 3-phase 600v AC that is applied to the stationary rectifiers
What has to be done prior to closing the Exciter Field Breaker on U1?
Voltage Regulators must be in Manual prior to closing
What must be done to open the Exciter Field Breaker?
Gen Output breakers must be OPEN! (O and O1 breakers for Unit 1 and A and A1 Breakers for Unit 2)
How are the output bushing cooled in U1?
Generator Gas (Hydrogen)
What delays, if any, does the Unit differential (Unit HEA) relay have?
- 30 sec delay after a Rx trip
(allows RCPs to coast down to cool) - No delay for Transformer or Generator Trips
What provides power to the Unit Diff Relay (Unit HEA)?
250v DC (Train B)
What provides power to the Overall Diff Relay (Overall HEA)?
Switchyard 125 VDC
What provides power to 33 VED (Turbine Trip Relay)?
250v DC Train A
What is the H2 cooling flow path?
turbine and collector ends, gen rotor and stator core, hydrogen coolers
What is MVARS in?
capacitive / under-excited
What is MVARS out?
Inductive / over-excited
What can being underexcited cause?
slipping of poles
How should the Generator Synchoscope rotating before closing the output breakers? What does this mean?
Slowly in the fast direction.
Gen Frequency should be higher than Grid Frequency
How are the Generator Rectifiers cooled for both units?
Natural Circulation of Air
What do the Thyrister Converters do in Unit 1?
Regulate the firing angle to change the voltage of field of the main exciter
What does the H2 cool on the U1 Generator?
The rotor
If you lose the main generator excitation system on U1, will the U1 Main Generator trip?
Yes
The generator will lose excitation; the Unit HEA relays will be energized
What is the Gen Conditon Monitor looking for in the generator?
Products of combustion
What is the DIRECT action that occurs when the Emergency Unit Trip Pushbutton is depressed?
Unit Differential relays operate
What has to be done prior to opening the Exciter Field Breaker?
Both generator output breakers must be open for Exciter Field Bkr to open
(O and O1 breakers for Unit 1 and A and A1 Breakers for Unit 2)
What are the common Unit and Overall HEA Actions?
- Turbine Trip
- Trip Exciter Field Breaker
- Turn excitation OFF
- Trip generator output breakers
- Fast Transfer from UAT to RAT
- Start time delay circuits for breaker failure
- Start sequence monitor and oscillograph
- Arms Main Transformer Deluge
- DCS input
- Enables shutdown of Main Transformer Cooling
What are the Unit HEA Actions?
- Disables Main Generator - Neutral Ground Relay
- Disables 26 KV Iso Phase Bus Neutral Ground
- Trips Stator Water Pumps
- Alarm “Unit Differential Operated”
What is on TDB 11-5 (Main Gen Capability Curve)?
MVARS and H2 Pressure inputs
If you have a channel fault on your voltage regulator, what will happen?
it will swap to standby channel
If Voltage regulator system calls for swap to other channel or to Manual and the swap fails to occur, what happens?
In 2-3 secs, an Excitation Trip will occur
What are the 33 VED (Turbine Trip Relay) actuation signals with no delay?
All 4 Main Turbine Stop Valves are closed, and At least one valve out of each of the Reheat Stop/Intercept Valve pairs is closed(U-1). Plus control valves in U-2.
AND
Trips Overall HEA
When does the Unit and Overall HEA’s not have a 30 Sec delay?
on a transformer trip or generator trip
What is the flow path of U1 Main Generator?
600v AC => Step Down Transformer (167v AC) => Exciter Field Bkrs => Voltage Regulators (v DC) => Slip Rings => Main Exciter (v AC) => Field Rectifiers (v DC) => Slip Rings => Main Gen (AC) => Main Transformer
When in auto on the voltage regulator, the Unit 1 voltage regulator senses the output of what?
The Main Generator
When is the Emergency Unit Trip Push Button Used to Trip the Generator?
When a motoring condition exists. Do not use if steam is being applied to the turbine, it can overspeed it
Which Unit has the Pilot Exciter? What does it do?
Unit 2. It is a Permanent magnet
- Supplies AC power to Voltage Regulator
- Produces excitation current for Main Exciter
What is the flow path for the Unit 2 Main Generator?
Pilot Exciter (600v AC) => Step Down Transformer (78v AC) => Exciter Field Bkrs => Voltage Regulators (v DC) => Slip Rings => Main Exciter (v AC) => Field Rectifiers (v DC) => Slip Rings => Main Gen (AC) => Main Transformer
What do the Thyrister Converters do in Unit 2?
changes the output of the pilot exciter to DC
How are the output bushing cooled in U2?
Stator Cooling Water
What controls Generator voltage when the Automatic Voltage Regulator is in automatic?
Generator terminal voltage sensed at the PT’s
What conditions would allow an immediate generator trip upon a Turbine trip?
A Turbine Trip occurs and the reactor trip breakers are closed and no SI or Hi-Hi SG level exists
What prevents an inadvertent loss of excitation at power if the exciter field breaker was opened?
Generator breakers must be opened for the switch to open the exciter field breaker
What is the typical temperature difference between cold gas and stator water? Why?
Stator Water temperature is usually 3-4°C warmer than Cold Gas temperature to prevent condensation
Can you operation the generator if Generator seal oil is lost?
No, you’ll have trip the generator and do emergency degas
What does the “Generator CBs Failure Trip” Push Button do?
Isolate all breakers downstream of the Generator Output Breakers. Designed to stop motoring if the Generator Output Breakers do not open
Unit 1 is worse than Unit 2 bc it kills Reserve Feed to Opposite Unit
What creates the Generator Field?
The Rotor
What is the Main Exciter powered by in each unit?
Unit 1 = 600 VAC ONLY
Unit 2 = Pilot Excitor (permanent Magnet Generator) and 600 VAC backup
What’s the purpose of the V/Hz relay?
Provide protection against overexcitation by actuation of an alarm and trip of the Overall HEA Differential relays.
What is the Unit Response if the exciter field breakers do open (magically) during normal power operation?
Generator will lose excitation and the Unit HEA relays will be energized.
