Main Generator Flashcards
What is the basic design of the main generator?
- Hydrogen Inner Cooled
- 3 phase
- 60 Hz
- 1800 RPM
- 4-Pole
What is the Stator?
Armature windings in which output voltage is developed.
Rated at 25,062 amps and 22,000 volts.
What is the Rotor?
Contains the field windings for voltage generation.
Rated at 7,432 amps and 500 volts.
What is the Exciter?
A three-phase AC generator whose output (500 VAC at 400 Hz) is rectified (converted to DC) by rotating rectifier wheels on the generator shaft.
Provides field excitation current to the rotor (field windings) to produce a magnetic field.
What is the Permanent Magnet Generator?
A series of permanent magnets mounted on rotating shaft.
Conductors wound on a stationary segment. As shaft rotates AC voltage is produced. This AC powers the Voltage Regulator and provides power to be amplified/rectified for generator field excitation.
What are the Rectifier Wheels?
Located on the shaft.
Rectify exciter AC current to DC current for Main Gen field windings (rotor).
Contain diodes, resistors, capacitors, fuses, and blown fuse indicators.
What is the field breaker?
Connects PMG output to exciter stator windings (via voltage regulator) and to Power Supply Unit for Voltage Regulator.
Breaker handswitch on C-01.
Control power from D-11-2.
What is the voltage regulator?
The voltage regulator controls the field strength of the exciter to maintain the generator’s voltage output constant at its setpoint, if in automatic.
- Inputs: Exciter current and Main Gen terminal voltage.
- Outputs: Signals to Trinistat Power Unit to control amount of excitation.
Trinistat Firing Circuits send firing pulses to the Trinistat Power Amplifier, which varies the AC Exciter stator field current. Cabinet on South Mezzanine.
Handswitches on C-01
What is the Trinistat Power Unit?
Consists of Redundant Firing Circuits, Power Amplifiers, and 24V power supplies. Provides adjustable DC voltage to exciter field winding.
Control via input from DC Adjuster and AC Adjuster.
Range of adjustment is 0-330 of sine wave input.
What is the DC adjuster?
- Provides direct vice automatic control of field excitation.
- Control is by changing the reference signal. Senses exciter field current (DC) and compares to adjustable reference signal (controlled via handswitch on C-01).
- Resultant error is applied to Trinistat circuits (via a motor operated transformer, i.e., potentiometer) to maintain exciter field current at a set reference value.
- Terminal voltage will vary with turbine speed, load, and grid conditions.
- Powered from D-11-2. Fails as is - exciter will still provide field to generator, but voltage cannot be adjusted.
What is the AC adjuster?
Provides automatic control of field excitation.
Senses Main Generator terminal voltage (AC) and compares it to an adjustable reference signal. Error signal sent to Trinistat Power Unit to control excitation such that a constant terminal voltage is maintained.
Note: There is some voltage droop built into the circuit. Prevents the voltage regulator from trying to maintain the entire grid voltage at a constant value.
When AC Regulator is in service, the DC Adjuster has no control over voltage, but its signal is still present if the auto circuit fails.
What is the Regulator Balance Meter?
Indicates the difference between DC and AC adjuster outputs.
Automatically maintained near zero (DC Adjuster tracks AC Adjuster output) via regulator “following” circuits for a bumpless transfer between AUTO and MANUAL control.
How is the Exciter cooled?
Utilizes a shaft mounted air blower and 2 coolers with each cooler having 2 cooling coils. Cooled by non-critical Service Water.
TCV-0852 provides automatic temperature control of the air space inside the exciter housing to 108º - 122ºF.
Temperature indication is via two RTDs (one at each end of the exciter). These two temperatures are balanced to within 3ºC (2º preferred) of each other.
10 seconds of no cooling results in Exciter Damage.
How is the Exciter ventilated?
An exhaust fan on top of the exciter housing with plug providing power is located on east side of Exciter housing.
Panel showing indicating lights for the fan is located at the Turbine end of the Main Generator on box JL-145. Local control switch, HAND/OFF/AUTO, inside JL-145.
- Auto: Fan shuts off when turbine speed is above 600 rpm. During a turbine shutdown, fan comes on when shaft speed reaches 600 rpm.
What is the cycle of the hydrogen dryer?
One tower is in service while other is in regeneration.
The in-service tower removes moisture for 8 hours.
The tower in regeneration heats (driving out moisture) for 4 hours, and cools down for 4 hours.
What provides the motive force for hydrogen circulation through the driver?
The generator blower and is assisted by a small muffin fan mounted on bottom of tower.
The fan allows the Hydrogen Dryer to be in service when the Main Generator is on the turning gear and pressurized.
What are the hydrogen dryer performance indicators?
HI-2244, Generator Hydrogen Dewpoint indicator should be reading < 4.5º C and liquid detectors should indicate no condensation.
When regenerating, what is the target temperature of the reactivator *hydrogen” gas.
The reactivator gas flow is adjusted to achieve a target temperature of 200 - 230º F at the end of the heating cycle.
What results from the failure of the hydrogen dryer moisture separator drain trap?
Potential source of hydrogen escaping to the turbine bldg.
A malfunctioning moisture separator, or loss of the reactivator gas could mean inadequate moisture removal from the generator hydrogen when the tower goes back into service.
