Main Generator

Question 1

What are the modes of operation of the voltage regulator?

Answer 1

OFF - manual (DC adjuster)
TEST - manual (DC adjuster). AC adjuster gets power, but is not controlling
ON - auto (AC adjuster)

Question 2

How does the voltage regulator operate in auto mode (AC adjuster)?

Answer 2

Senses generator voltage (terminal voltage) and maintains it at setpoint

Question 3

How does the voltage regulator operate in manual mode (DC adjuster)?

Answer 3

• Senses exciter field and compares it to a reference signal (set by the operator in the control room) and tells firing circuit when to fire (raise/lower field excitation)
• No limiters while in manual.
• Manual tracks auto for bumpless transfer.

Question 4

How does the voltage regulator, exciter, and generator work to produce voltage to be sent to the grid?

Answer 4

• PMG on rotor induces a voltage that is sent through the field breaker to power the voltage regulator.
• Voltage regulator looks at terminal voltage and outputs a DC voltage to the exciter field windings.
• Exciter field induces a voltage on the rotor in the exciter.
• This voltage is rectified to DC, which is supplied to the windings on the rotor in the generator.
• DC voltage in the rotor windings induces a voltage (22 KV) on the stator in the generator.
• 22 KV from the stator is then sent to the main transformer, where it is transformed to 345 KV and sent to the grid.

Question 5

What is the purpose of the permanent magnet generator?

Answer 5

Provides power to the voltage regulator for field excitation

Question 6

What is the purpose of the exciter?

Answer 6

Provides current to the rotor field

Question 7

What is the purpose of the rectifier wheels?

Answer 7

Turns AC current from the exciter to DC current to be supplied to the main generator field windings on the rotor.

Question 8

What is the required response to blown fuses on the rectifiers?

Answer 8

• 1 fuse blown - contact system engineer
• 2 fuses blown for 1 phase - shutdown within 24 hours and monitor every 4 hours
• 3 fuses blown for 1 phase - < 15% power, trip the turbine. > 15% power, trip the reactor

Question 9

What is the purpose of the field breaker?

Answer 9

Connects the PMG to the voltage regulator

Question 10

What happens if the field breaker is opened while at power?

Answer 10

Loss of excitation alarm and 386P relay actuates, which will trip the plant

Question 11

What is the process for transferring the voltage regulator from manual to auto?

Answer 11

• Take voltage regulator switch to test
• Match output of the AC and DC adjusters by ensuring regulator balance meter is at 0. Accomplished by raising/lowering AC adjust switch
• Once regulator balance meter is at 0, take voltage regulator switch to on

Question 12

What is the function of the 386P/B relays?

Answer 12

Trips the turbine/generator on electrical faults that would make you not want to use the coast down feature.

Question 13

What happens when the 386P/B relays actuate?

Answer 13

• Turbine trip
• Generator trip
• Exciter trip
• Fast transfer of electrical buses to startup power immediately

Question 14

What is the function of the 386C relay?

Answer 14

Trips the turbine/generator on non-electrical faults that you would want to use the coast down feature.

Question 15

What happens when the 386C relay actuates?

Answer 15

• Turbine trip
• Generator trip
• Exciter trip
• Fast transfer of electrical buses to startup power after 10 seconds

Question 16

What is the function of the minimum excitation limiter?

Answer 16

• Only works with AC adjuster

- 21.7 KV minimum excitation

Question 17

What is the function of the loss of field relay?

Answer 17

• Caused by voltage regulator malfunction, or opening of the field breaker
• Plant trip on 386P

Question 18

What is the function of the volts/Hz limiter?

Answer 18

• Limits terminal voltage to 23.1 KV
• Only works with AC adjuster
• If limiter fails to retard voltage, at 23.54 KV plant trips on 386P

Question 19

What is the function of the maximum excitation limiter?

Answer 19

• Limits field current to 273 amps

- Only works with AC adjuster

Question 20

What is the function of the regulator over excitation module?

Answer 20

• 283 amps field current for greater than 33 seconds, then voltage regulator swaps to manual
• If problem persists for more than 3 seconds after swap to manual, plant trips on 386P

Question 21

What is the purpose of the stator coil hot gas temperature PPC alarm?

Answer 21

• alarms at 8 C differential temperature

- indicates a hot spot in the stator, and there may be generator damage

Question 22

What is the consequence of high cold gas temperature?

Answer 22

Reduces the life of gaskets and seals, and eventual H2 leak