Main Generator

DC exciter field _____ AC current in shaft mounted exciter

Where are the armature and the field located on the main generator?

Explain how capacity is increased in the Main Generator

Limits fault current of ground within generator or on 22kV system

Two cooling units, each with:
–HX (TPCW cooled)
–Forced air recirculation fan
–At least 1 cooling unit operating when generator is operating

Used for voltage regulation
Used to measure phase current for relay protection and metering

To automatically close the breaker between the incoming generator and running bus when they are nearly matched in speed and phase

Locks out synchronizer if the breaker does not remain closed > 15 cycles (10 seconds)

Auto resets if breaker remains closed.

HIR Brushless type consisting of:
•Permanent magnet AC generator
–Rotating magnet
–Stationary windings
•AC generator
–Stationary electromagnet
–Rotating windings
–Rotating diode rectifier assembly
•All mounted on common shaft

May uncouple rotor field from grid. Rotor falling out of step with system causes large damaging torques/currents.
Slip Poles
Loss of Synchronization

Center cubicle contains 2 power amp drawers

AC regulator controls when regulator switch is ON
AC regulator compares: Generator output voltage (Potential Transformers) AND 24 VDC reference voltage (as adjusted by the AC Regulator Adjust Control)
Error signal changes output in the same manner as the DC regulator
Signal mixer takes error signal and subjects it to excitation & V/HZ limits.
Keeps DC regulator setup for bumpless transfer from AC to DC control.

Two amplifiers - Outputs paralleled - Either amp can support full power operation

DC regulator controls when regulator switch is OFF or in TEST

Extreme under excitation may lead to loss of synchronization. Not enough magnetism in rotor to couple rotor to grid. May "slip poles" as rotor loses coupling to stator damaging generator.

Reduces excitation if high values are reached after variable time delay

Limits voltage to frequency ratio

Warns of excessive exciter current.
Prevents damage of stator

Deals with excitation/regulation system failure causing over-excitation

If in DC regulation, large load reject will cause generator volts to increase. Not corrected until DC regulator manually adjusted.

If above OVP setpoint, module limits maximum generator output voltage to 24.2 kV by direct control of firing circuits.

ICL #2 output to signal combiner to limit pulse firing circuit input if exciter field current is too high

Avoids mechanical and electrical generator damage by tripping the generator

Generator trip on turbine trip to avoid motorizing generator off grid and spinning turbine without steam flow. - overheat last stages of LP Turbine, generator windings, and rotor magnets.
Primary generator protection from lockout relay 286G

Simultaneously trips both generator breakers (Ann F 3/1 & F 3/2)
Trips 20/AST and/or 20/ASB solenoids to trip turbine (Ann E 6/5)
Trips generator exciter field breaker
Transfer of 4kV buses to S/U transformer
Trips EDG output breakers (if closed) on affected unit.

Starts 30 sec. time delay and actuates annunciator E 7/5 (peak decay heat)

Either turbine exhaust hood temp >250°F with turbine loaded and turbine stop or control valves closed actuates relay 274EHT

Protects against generator output breaker closure with generator out of sync w/grid.

When either set senses <57.0 Hz with either generator breaker closed they actuate a 12 sec. time delay to

Curve specifies MW and MVARS limits for specific H2 pressures.
Maximum MW (and MEGAVARS) allowed decreases as Hydrogen pressures decreases.
Lagging MEGAVARS section is limited by rotor heating.
Leading MEGAVARS section is limited by stator core heating.
PF between ≈0.95 leading to ≈0.85 lagging the MW limit prevents excessive stator heating.
High MW loads result in excessive stator winding temperature rise.
The exciter limiter setting ensures that operation will not occur below the steady state stability limit.
Below the steady state stability limit the generator could fall out of synchronization.

Means for safely
Adding/extracting hydrogen from the generator
Carbon dioxide as a scavenging medium
Maintains gas pressure
Indicates condition of the generator with regard to gas pressure, temperature, and purity
Indicates generator liquid level
Removes water vapor
Efficient cooling and heat transfer medium for the generator
Monitors generator windings for insulation breakdown

Supplies lubricating oil
ØLubricate seals
ØPrevent escape of hydrogen
ØWithout introducing
air
moisture

Designed to remove the heat generated by current flow
At 75 psig Hydrogen
Generator capacity is 760 MW with 23,464 amps per phase
Without exceeding any temperature or design limits
CO2 - scavenging gas to prevent air and hydrogen from mixing within the generator

Maintains oil pressure at the seals 12 psid greater than hydrogen pressure
Air side and hydrogen side are kept within +2" water pressure of each other
Minimize the amount of oil interchange between the two systems
Reduces the amount of hydrogen needed to maintain generator purity
Reduces the amount of contaminants introduced into the generator

Boundary against hydrogen leakage around generator shaft
Pressure maintained at 12 psid greater than hydrogen
Two seal oil systems
Air side seal oil system
Hydrogen side seal oil system
Reduces the amount of hydrogen used and the amount of contaminants introduced into the hydrogen

Prevents the hydrogen from leaking out
Pressure at the seals decreases to 8 psid
Equalizing valve opens to admit high pressure main lube oil into seal oil system
Reduced to 125 psig and routed to the gland seals
Excess oil sent back to the main oil reservoir via a loop seal

Δp drops to 5 psid
Air Side DC Seal Oil Backup Pump auto starts

Loop seal tank suction - discharges to the seals like the air side seal oil pump
DC powered
Available upon Loss of AC
Continues to run - must be shut off manually

Generator capacity higher than with air
low density gas
high thermal conductivity and heat transfer coefficients
Capacity increased with pressure in the generator
Higher density and more mass for heat removal
Lower windage and ventilating losses
Maintenance of the generator is reduced due to the freedom from dirt and moisture
Life of the winding insulation is increased because of the absence of oxygen and moisture

Hydrogen and air explosive mixture _% to __% hydrogen in air by volume
Most dangerous situation is about __%

From the Units 1 & 2 gas house ( or local bottle manifold)
Turbine operator change the cylinders
Purge should not be initiated unless 25 bottles are on hand
Added via the manifold
15 bottles to achieve 95% purity
10 additional bottles may be required to reach a purity >95%

Used to purge the CO2 with a temporary hose
Through purge filters
Second temporary hose from purge filters to a test connection
Before purging the generator, the filters must be changed out
Located at the hydrogen supply/purge manifold
Admitted to generator must pass through filters
Minimal dirt and moisture added to the generator
Generator pressure maintained below 2 psig
Purge as long as necessary

Low hydrogen purity ____%
High hydrogen purity ____%

Generator hydrogen gas cooled by coolers mounted in the generator housing

Controls generator atmosphere relative humidity
Makes it unnecessary to monitor or otherwise control the generator relative humidity
Connected across the high and low pressure zones in the ventilating circuit of the generator
H2 circulated through when the generator is running
Activated alumina absorbs moisture
Removed from service if generator is filled with anything other than hydrogen
Crystals turn grayish-pink when saturated with moisture
Dryer crystals are reactivated
Lined Up
Blower started
Heaters turned on
Reactivated for 4 hours or until the crystals turn light blue
Powered from MCC A, breaker 0566

With Seal Oil prevent loss of hydrogen from generator
Two sets encircle the generator shaft
exciter end
turbine end
Rings move radially with the shaft
Restrained from rotating by pins
Oil is fed by Seal Oil System through passages in the supporting brackets
Gland ring restricts the oil flow through the seal
Oil flows from these grooves both ways along the shaft through the clearance space between the shaft and the gland ring
Oil leaving the gland seal rings is caught in chambers on each side of the seal and drained back to the Seal Oil system

Closed loop system - limits the escape of hydrogen and the entry of oxygen
Oil from gland seal rings drains to a defoaming tank (one on each end)
Hydrogen side drain regulator maintains the hydrogen side oil inventory

Takes suction on the drain regulator and discharges through the hydrogen side seal oil cooler to the gland seals
Powered from MCC A, breaker 0503
START-STOP Pushbuttons on H2 control panel

Turbine Plant Cooling Water circulated through the tubes
Oil on the shell side of the cooler
Oil outlet temperature of 80-120°F
Cooler design requires isolation of both the tube and shell sides for maintenance