Week 3: Main Generation

Question 1

What subsystems comprise the Main Generation System?

Answer 1

Main Generator
Excitation System
Main Distribution System

Question 2

What is the function of the Main Generator?

Answer 2

To convert the mechanical power of the turbine into electrical power.

Question 3

What is the design output of the Main Generator?

Answer 3

25,000 Volts with a 0.9 lagging power factor via 1800 rpm field rotation.

Question 4

What is the definition of power factor?

Answer 4

The ratio of working power to apparent power. Depending on the load, a certain percentage of the plants output (apparent power) will be lost as reactive power, which does no work and is instead lost through heating of the transmission lines.

Question 5

What are the primary components of the Main Generator, and how are they cooled?

Answer 5

The stator is the stationary portion of the generator, and is cooled by demin water.
The rotor is the rotating portion of the generator, and is cooled by hydrogen gas.

Question 6

What are the pros and cons to using H2 to cool the Main Generator rotor?

Answer 6

Pros:
High thermal conductivity
Low density minimizes windage losses
Excludes air, which preserves insulation
Arcing and corona effects are reduced
Cons:
Explosive in air at most concentrations
Must be purged for maintenance and then replaced for subsequent operation
Continual small leaks - requires constant makeup

Question 7

What is the function of the Excitation System?

Answer 7

To provide a regulated electric current that produces the magnetic field in the turbine rotor when starting up, then to regulate the output voltage of the Main Generator while operating.

Question 8

Describe the operation of the Excitation System.

Answer 8

The exciter is a self-excited generator, meaning that it supplies its own electrical field via a separate rotor attached to the main shaft of the turbine. The resulting excitation current is then supplied to the Main Generator rotor.

Question 9

What is the function of the Exciter Manual (DC) Regulator?

Answer 9

The DC regulator is used when initially starting the generator to monitor the exciter output voltage and compare it to a reference voltage, generating an error signal for downstream control equipment.

Question 10

What is the function of the Exciter Auto (AC) Regulator?

Answer 10

The AC regulator is used to automatically vary the exciter field current as necessary to regulate the output voltage of the Main Generator.

Question 11

Describe how the Exciter system is started.

Answer 11

A separate DC source must be used to flash the exciter field. The DC field Flash component is automatically energized for 10s when the exciter field breaker is closed, allowing the exciter voltage to build up to the point where it is self-sustaining.

Question 12

What is the function of the Main Distribution System?

Answer 12

To connect the main generator output with the offsite transmission lines, as well as supply power to house loads via onsite and offsite sources.

Question 13

Describe the components of the Main Distribution System.

Answer 13

Main XFMR
Unit Aux XFMR
Startup XFMR
ESF XFMRs
Safeguards XFMRs
Service buses PA01 and PA02
Safeguards buses NB01 and NB02
Diesel Generators NE01 and NE02

Question 14

What is the function of the Main Transformer?

Answer 14

To step up the voltage from the Main Generator to 345kV for offsite transmission. Note that the output from the generator to the Main transformer has a very high current density and requires special cooling.

Question 15

What is the function of the Unit Aux Transformer?

Answer 15

To supply power to the service buses when the plant is operating.

Question 16

What is the function of the Startup Transformer?

Answer 16

To supply offsite power to the service buses and 1/2 ESF XFMRs when the main generator is offline.

Question 17

What is the function of the ESF Transformers?

Answer 17

To supply offsite power to the safeguards buses via diverse means.

Question 18

What is the function of the Safeguards Transformers?

Answer 18

To provide offsite power to the ESF XFMR not powered by the Startup XFMR.

Question 19

What is the function of the Service Buses?

Answer 19

To provide power to non-safety plant loads. Normally powered by the Unit Aux XFMR.

Question 20

What is the function of the Safeguards Buses?

Answer 20

To provide power to safety-related plant loads. 1 bus normally powered by Safeguards XFMR and the other by Startup XFMR through the respective ESF XFMR.

Question 21

What is the function of the Diesel Generators?

Answer 21

To provide backup power to the Safeguards buses in the event that offsite power is not avaliable.

Question 22

What are the Main Generator Auxiliary Systems?

Answer 22

H2 and CO2 Gas Control System
Hydrogen Seal Oil System
Stator Cooling Water System

Question 23

What is the function of the H2 and CO2 Gas Control System?

Answer 23

To supply H2 to the generator
To cool the H2 in the generator with service water
To monitor and maintain H2 purity and pressure
To provide CO2 gas for Air/H2 purging for maintenance

Question 24

What is the function of the Hydrogen Seal Oil System?

Answer 24

To ensure that H2 does not leak out of the generator
To ensure air does not leak into the generator

Question 25

What is the function of the Stator Cooling Water System?

Answer 25

To cool the generator stator windings, electrical output bushing, and exciter rectifier banks with high-purity demin water.

Question 26

When not connected to the grid, how is Turbine Speed controlled? Generator Voltage?

Answer 26

Turbine speed is dictated by the position of the Turbine Control Valve
Generator voltage is determined manually via the manual exciter regulator

Question 27

When connected to the grid, how is Generator frequency/voltage controlled? How would you adjust the reactive power?

Answer 27

The Grid determines the Generator frequency/voltage, as per the automatic exciter regulator
Reactive power can be controlled by varying the voltage of the automatic exciter regulator