Generator and Excitation

Question 1

What causes Generator Unit Differential (Unit HEA) to roll?

Answer 1

• **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

Question 2

What causes the Generator Overall Differential (Overall HEA) to roll?

Answer 2

• Turbine Trip (33VED)
• Breaker Failure Relays (trips other yard bkrs)
• Reverse power (Gen Motoring U1)

Question 3

What does the Main Exciter do?

Answer 3

Generates 3-phase 600v AC that is applied to the stationary rectifiers

Question 4

What has to be done prior to closing the Exciter Field Breaker on U1?

Answer 4

Voltage Regulators must be in Manual prior to closing

Question 5

What must be done to open the Exciter Field Breaker?

Answer 5

Gen Output breakers must be OPEN! (O and O1 breakers for Unit 1 and A and A1 Breakers for Unit 2)

Question 6

How are the output bushing cooled in U1?

Answer 6

Generator Gas (Hydrogen)

Question 7

What delays, if any, does the Unit differential (Unit HEA) relay have?

Answer 7

• 30 sec delay after a Rx trip
  (allows RCPs to coast down to cool)
• No delay for Transformer or Generator Trips

Question 8

What provides power to the Unit Diff Relay (Unit HEA)?

Answer 8

250v DC (Train B)

Question 9

What provides power to the Overall Diff Relay (Overall HEA)?

Answer 9

Switchyard 125 VDC

Question 10

What provides power to 33 VED (Turbine Trip Relay)?

Answer 10

250v DC Train A

Question 11

What is the H2 cooling flow path?

Answer 11

turbine and collector ends, gen rotor and stator core, hydrogen coolers

Question 12

What is MVARS in?

Answer 12

capacitive / under-excited

Question 13

What is MVARS out?

Answer 13

Inductive / over-excited

Question 14

What can being underexcited cause?

Answer 14

slipping of poles

Question 15

How should the Generator Synchoscope rotating before closing the output breakers? What does this mean?

Answer 15

Slowly in the fast direction.

Gen Frequency should be higher than Grid Frequency

Question 16

How are the Generator Rectifiers cooled for both units?

Answer 16

Natural Circulation of Air

Question 17

What do the Thyrister Converters do in Unit 1?

Answer 17

Regulate the firing angle to change the voltage of field of the main exciter

Question 18

What does the H2 cool on the U1 Generator?

Answer 18

The rotor

Question 19

If you lose the main generator excitation system on U1, will the U1 Main Generator trip?

Answer 19

Yes

The generator will lose excitation; the Unit HEA relays will be energized

Question 20

What is the Gen Conditon Monitor looking for in the generator?

Answer 20

Products of combustion

Question 21

What is the DIRECT action that occurs when the Emergency Unit Trip Pushbutton is depressed?

Answer 21

Unit Differential relays operate

Question 22

What has to be done prior to opening the Exciter Field Breaker?

Answer 22

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)

Question 23

What are the common Unit and Overall HEA Actions?

Answer 23

• 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

Question 24

What are the Unit HEA Actions?

Answer 24

• Disables Main Generator - Neutral Ground Relay
• Disables 26 KV Iso Phase Bus Neutral Ground
• Trips Stator Water Pumps
• Alarm “Unit Differential Operated”

Question 25

What is on TDB 11-5 (Main Gen Capability Curve)?

Answer 25

MVARS and H2 Pressure inputs

Question 26

If you have a channel fault on your voltage regulator, what will happen?

Answer 26

it will swap to standby channel

Question 27

If Voltage regulator system calls for swap to other channel or to Manual and the swap fails to occur, what happens?

Answer 27

In 2-3 secs, an Excitation Trip will occur

Question 28

What are the 33 VED (Turbine Trip Relay) actuation signals with no delay?

Answer 28

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

Question 29

When does the Unit and Overall HEA's not have a 30 Sec delay?

Answer 29

on a transformer trip or generator trip

Question 30

What is the flow path of U1 Main Generator?

Answer 30

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

Question 31

When in auto on the voltage regulator, the Unit 1 voltage regulator senses the output of what?

Answer 31

The Main Generator

Question 32

When is the Emergency Unit Trip Push Button Used to Trip the Generator?

Answer 32

When a motoring condition exists. Do not use if steam is being applied to the turbine, it can overspeed it

Question 33

Which Unit has the Pilot Exciter? What does it do?

Answer 33

Unit 2. It is a Permanent magnet - Supplies AC power to Voltage Regulator - Produces excitation current for Main Exciter

Question 34

What is the flow path for the Unit 2 Main Generator?

Answer 34

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

Question 35

What do the Thyrister Converters do in Unit 2?

Answer 35

changes the output of the pilot exciter to DC

Question 36

How are the output bushing cooled in U2?

Answer 36

Stator Cooling Water

Question 37

What controls Generator voltage when the Automatic Voltage Regulator is in automatic?

Answer 37

Generator terminal voltage sensed at the PT’s

Question 38

What conditions would allow an immediate generator trip upon a Turbine trip?

Answer 38

A Turbine Trip occurs and the reactor trip breakers are closed and no SI or Hi-Hi SG level exists

Question 39

What prevents an inadvertent loss of excitation at power if the exciter field breaker was opened?

Answer 39

Generator breakers must be opened for the switch to open the exciter field breaker

Question 40

What is the typical temperature difference between cold gas and stator water? Why?

Answer 40

Stator Water temperature is usually 3-4°C warmer than Cold Gas temperature to prevent condensation

Question 41

Can you operation the generator if Generator seal oil is lost?

Answer 41

No, you'll have trip the generator and do emergency degas

Question 42

What does the “Generator CBs Failure Trip” Push Button do?

Answer 42

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

Question 43

What creates the Generator Field?

Answer 43

The Rotor

Question 44

What is the Main Exciter powered by in each unit?

Answer 44

Unit 1 = 600 VAC ONLY Unit 2 = Pilot Excitor (permanent Magnet Generator) and 600 VAC backup

Question 45

What's the purpose of the V/Hz relay?

Answer 45

Provide protection against overexcitation by actuation of an alarm and trip of the Overall HEA Differential relays.

Question 46

What is the Unit Response if the exciter field breakers do open (magically) during normal power operation?

Answer 46

Generator will lose excitation and the Unit HEA relays will be energized.