Main Generator

  1. DC exciter field _____ AC current in shaft mounted exciter
  2. Where are the armature and the field located on the main generator?
    Electrically the stator is the armature and the rotor is the field.
  3. Explain how capacity is increased in the Main Generator
    Generator capacity increased by use of pressurized Hydrogen - High conductivity & heat transfer coefficients - reduced windage and ventilation losses

    pure H2 is non-corrosive
  4. Limits fault current of ground within generator or on 22kV system
    Generator Neutral Transformer
  5. Two cooling units, each with:
    –HX (TPCW cooled)
    –Forced air recirculation fan
    –At least 1 cooling unit operating when generator is operating
    Isolated Phase Bus
  6. Used for voltage regulation
    Used to measure phase current for relay protection and metering
    22kV Bus Potential & Current Transformers
  7. To automatically close the breaker between the incoming generator and running bus when they are nearly matched in speed and phase
    Automatic Generator Synchronizer

    Synch lights - Bright when generator/grid 180° out of phase (max current) - Dark when in phase (zero current)
  8. Locks out synchronizer if the breaker does not remain closed > 15 cycles (10 seconds)

    Auto resets if breaker remains closed.
    Anti Pumping Circuit
  9. 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
  10. May uncouple rotor field from grid. Rotor falling out of step with system causes large damaging torques/currents.
    Slip Poles
    Loss of Synchronization
    Loss of Field
  11. Center cubicle contains 2 power amp drawers
    Exciter Switchgear
  12. 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.
    Voltage Regulation
  13. Two amplifiers - Outputs paralleled - Either amp can support full power operation
    Voltage Regulation - Power Amplifiers
  14. DC regulator controls when regulator switch is OFF or in TEST
    Voltage Regulation - DC Regulation
  15. 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.
    Voltage Regulation - Minimum Excitation Limiter (MEL)
  16. Reduces excitation if high values are reached after variable time delay
    Voltage Regulation - Maximum Excitation Limiter (MXL)
  17. Limits voltage to frequency ratio
    Voltage Regulation - Volts per Hertz Limiter (HXL)
  18. Warns of excessive exciter current.
    Prevents damage of stator
    Voltage Regulation - Field Forcing Alarm
  19. Deals with excitation/regulation system failure causing over-excitation
    Voltage Regulation - Over-Excitation Protection (OXP)
  20. 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.
    Voltage Regulation - Over-voltage Limiter (OVP)
  21. ICL #2 output to signal combiner to limit pulse firing circuit input if exciter field current is too high
    Voltage Regulation - Current Limiters
  22. 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
    Generator Protection
  23. 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.
    Either primary or backup generator lockout relays provide generator protection as follows
  24. Starts 30 sec. time delay and actuates annunciator E 7/5 (peak decay heat)
    Generator Mechanical Protection – Turbine Anti-Motoring trip
  25. Either turbine exhaust hood temp >250°F with turbine loaded and turbine stop or control valves closed actuates relay 274EHT
    Generator Mechanical Protection - Turbine Blade Overheat Protection
  26. Protects against generator output breaker closure with generator out of sync w/grid.
    Generator Electrical Fault Protection Inadvertent Energization Generator Protection
  27. When either set senses <57.0 Hz with either generator breaker closed they actuate a 12 sec. time delay to
    Generator Electrical Fault Protection UF protection
  28. 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.
    Generator Capability Curve
  29. 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
    Hydrogen Gas System Functions
  30. Supplies lubricating oil
    ØLubricate seals
    ØPrevent escape of hydrogen
    ØWithout introducing
    Seal Oil System Function
  31. 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
    Generator Gas System Design Bases
  32. 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
    Seal Oil System Design Bases
  33. 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
    General Description: Seal Oil System
  34. 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
    Air Side Seal Oil Backup Supply
  35. 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
    Air Side Seal Oil Backup Pump

    • If Backup Seal Oil not available
    • Turbine is shut down and auxiliary lube oil pump is shut down
    • Turning gear or DC pumps are available
    • Pumps’ output pressure of 5 to 15 psig
    • Generator gas pressure decreased to 2 psig
  36. 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 Gas System
  37. Hydrogen and air explosive mixture _% to __% hydrogen in air by volume
    Most dangerous situation is about __%
    • 4% to 70%
    • 37%
  38. 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%
    Carbon Dioxide Supply
  39. 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
    Instrument Air Supply
  40. Low hydrogen purity ____%
    High hydrogen purity ____%
    • <90%
    • >101.6%
  41. Generator hydrogen gas cooled by coolers mounted in the generator housing
    • Turbine plant cooling water
    • Through the finned tubes
  42. 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
    Gas Dryer
  43. 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
    Generator Seal Rings
  44. 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
    Hydrogen Side Seal Oil
  45. 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
    Hydrogen Side Seal Oil Pump
  46. 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
    Hydrogen Side Seal Oil Cooler
Card Set
Main Generator
Main Generator