Maingenerator/turbine

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Author:
skrappie1
ID:
111824
Filename:
Maingenerator/turbine
Updated:
2015-12-02 09:56:23
Tags:
gen turb advanced systems
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Description:
main generator and turbine
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  1. Power limitations for valve testing?
    • >10% Rx power and </= 88% Rx power
    • -85-88% preferred
    • Allows other 3 governor valves opening margin for closing the governor valve
  2. Effects of a loss of D-11-2 on the main generator?
    • Lose voltage regulator controls
    • -voltage limiting function is still available
    • Lose MOD-389 position indication
    • Exciter field breaker will not auto open on a turbine trip (can still locally trip)
  3. Effects of a loss of D-11-1 on the main generator?
    • Lose position indication for generator output breakers 25F7 and 25H9 (they fail as is)
    • Lose certain protective relays
    • Cannot trip from C-01 or via 386P, 386C relays
    • Trips via 386B (different power supply)
  4. Actions for EK-0107 "Turbine no load pre-trip"?
    • Turbine trip will occur if this condition persists for 60 seconds.
    • If the generator did not automatically pick up load, manually load the generator to 20MW.
    • If the generator loading can not be increased manually, then reopen the generator output breakers or trip the turbine.
  5. Turbine exhaust temperature precaution
    • Turbine exhaust temperature should not exceed 217oF for an extended operation or 250oF for periods of 15 minutes or more
    • -prevents overheating the later stages of the LP turbine blading.
  6. Procedurally required trips on the main turbine?
    • Fuse failure in the exciter diode wheel (3 fuses in 1 phase)
    • Turbine differential expansion rotor long/short
    • Turbine high vibrations >/= 14 mils
    • Turbine no load pre-trip
    • Bearing oil pressure pre-trip
    • Thrust bearing pre-trip
    • EH system lo-lo level trip
    • DEH priority 3 alarms
    • -OPCO
    • -OPSDI
    • -WS fail
    • -MOTO
    • -CSTMN
    • -UPS on battery
  7. Turbine thrust position monitor
    • Alarms on pre-trip at 35 mils
    • Turbine trip at 40 mils
  8. Exciter regulator overexcitation module (OXP)
    • if field current continues to rise, at 283 amps the OXP actuates:
    • -after 33 seconds it trips voltage regulator to manual
    • -if overexcitation persists, relay 376-k3 actuates after 3 seconds and actuates 386P (plant trip)
    • -if the overexcitation is corrected, then the OXP resets

    The OXP forces voltage regulator output to a preset value to lower excitation
  9. Required parameters prior to synchronization to the grid?
    • RX power </= 13% (higher of delta-T or NI power)
    • Tave </= 540oF
    • PIC-0511, TBV controller output signal > 60% (>75% preferred)
  10. Interface valve turbine trips (balance beam)
    • Low vacuum (18-21"Hg)
    • Lube oil low pressure (5-7 psig)
    • Overspeed (110%)
    • Manual trip lever (front pedestal)
    • Solenoid trips (20/AST)
    • -MSIVs not full open
    • -Rx trip (clutch relay coils)
    • -generator trip (386P,B, or C)
    • -no load trip (<8 psid for >60 seconds across the HP turbine)
    • -manual pushbutton on C-01
    • -DEH initiated trips (loss of control power to the manual cabinet)
  11. 20/ET emergency trip solenoid valve trips
    • Direct EHC fluid trips
    • -auto stop oil pressure at 45 psig 2/3 logic
    • -either MSIV not full open
    • -ATWS actuation
    • -turbine thrust bearing trip >40 mils
  12. Exciter protective device Volts/Hertz limiter (VHL)
    • Designed to limit terminal voltage to 23.1 Kv by limiting the output of the AC adjuster. Does not work with the DC adjuster
    • Initiates alarm that the AC adjuster is being limited
    • If the VHL fails, this will pick up volts/hertz relay (395)
    • -alarms at 23.54 Kv
    • -trips the plant via the 386P lockout relay on an inverse time basis
    • Limits the ratio to 2.11v/hz
  13. Main generator field breaker
    • Connects the PMG output to the exciter stator windings (via the voltage regulator) and to the power supply unit for the voltage regulator
    • Control power is from D-11-2
  14. What does runback to 5% button on the DEH operators console do?
    • Not available when the turbine control is in manual
    • Runs the turbine back to 5% load at whatever rate you tell it to
    • Can stop the runback by pushing the runback to 5% button again
  15. Purpose of the Ramp pushbutton on C-01 for the HED system?
    • Normally used at 30% load after the shutoff valves are opened. This button energizes the circuit that regulates opening of the 6 inch reheater steam control valves (CV-0594/0595/0597/0598) to the MSRs over 2 hours.
    • -assures an acceptable rate of differential expansion between the LP turbine casing and rotor
  16. What happens on an actuation of backup (386B) turbine generator lockout relay?
    • Turbine trip
    • Fast transfer of electrical to offsite
    • Generator breakers trip
    • B/U transfer trip
    • Exciter trip (field breaker opens)
  17. Exciter protective device minimum excitation limiter (MEL)
    • Functions only with the AC adjuster
    • Limits AC adjuster from underexciting the generator
    • If terminal voltage drops low enough the plant will trip on underexcitation device 340
  18. DEH feedback loops
    • With feedback loops in service, any upset in the system will be fed back into the control loops, and the governor valves will be automatically positioned accordingly
    • -could result in exceeding power limits
    • Normally not in service
  19. Exciter protective device field ground detector panel (364)
    • Applies a DC test voltage from the generator field to ground and monitors the resultant current flow. Current flow is inversely proportional to the resistance
    • Can be manually initiated at the exciter control cabinet on the south mezzanine
    • Auto ground detection test is perfomed every 24 hours
    • Checks for ground and brush failures
    • If the exciter field current or voltage is fluctuating +/- 10%, remove the unit from service
  20. Impact of a loss of power to the DEH console?
    • Turbine trips if:
    • -both manual panel power supplies fail (24vdc)
  21. Effects of a loss of non critical service water on the main generator?
    • Exciter can overheat quickly (10 seconds)
    • If EK-0259 "Exciter cooler hi temp" (50oC) occurs, concurrent with a loss of non-critical service water
    • -Immediately trip the reactor
    • If exciter cold air temperature exceeds 80oC and the RX/turb has been tripped, then slow rotor speed by breaking vacuum rapidly to minimize windage induced friction heating of the exciter
  22. Main generator DC adjuster
    • Senses exciter field current (DC) and compares it to an adjustable reference signal
    • -an error signal is sent to the trinistat circuits to maintain exciter field current at a set reference value
    • Powered from D-11-2
    • -fails as is
    • --cannot adjust voltage
  23. Exciter protective device, maximum excitation limiter (MXL)
    • Limits the maximum field current to 273 amps to protect the exciter field windings (114% of rated 236 amps)
    • Functional only with the AC adjuster
    • Initiates an alarm that the voltage regulator output is being limited
    • You will also get the field forcing/overexcitation alarm
  24. Exciter protective device loss of field relay (340)
    • Caused by:
    • -regulator malfunction
    • -short circuit in the generator field
    • -accidental exciter field breaker trip
    • Alarms and trips the plant (386P) on abnormally low or loss of field
  25. What do you do if you get the field forcing/overexcitation alarm?
    • Select AC adjuster to OFF or TEST
    • Use the DC adjuster to control generator terminal voltage between 21Kv and 23Kv
  26. Purpose of the main turbine interface valve?
    • Normally held closed by auto stop oil pressure
    • -supplied by the MLO pump at 110 psig
    • -at 45 psig, the dump valve opens due to spring pressure overcoming oil pressure
  27. When increasing turbine load, why do we adjust the limiter prior to starting our load increase?
    Failure to raise the limiter will prevent the governor valves from opening, and will cause the DEH system to go to HOLD.
  28. What is the precaution for the Latch button on the DEH panel?
    The latch button on the DEH panel shall not be relamped when the turbine is latched due to a possible turbine trip.
  29. What are the effects of a loss of seal oil on the main generator?
    • Lose lubrication and cooling of the generator seals
    • Possible total loss of H2 and generator will overheat
  30. What do the rectifier wheels do on the main generator?
    Rectifies exciter AC current to DC current for the main generator field windings (rotor)
  31. What are the consequences of operating with a generator high cold gas temperature?
    • A high cold gas temperature can lead to high hot spot temperatures in the stator and reduce the life of the gaskets and seals
    • Can also cause turbine to generator shaft misalignments
    • Maintain cold gas temperatures 37-45oC
    • -lower limit prevents excessive condensation
  32. EHC low low level alarm and lockout
    • 7 5/8" from the tank bottom
    • The standby EHC pump is locked out (won't start)
    • The running pump will not trip on low-low level lockout
    • Reset on the back of C-04 (386 LFT) after level has been restored
    • The lockout brings in a red alarm light between the pump control switches
  33. What are the consequences of operating with a low main generator H2 purity?
    • Low purity reduces the heat removal capacity of the H2 gas.
    • This may result in end turbine vibration high alarm on the PPC
  34. Reheater control panel power supply and failure mode?
    • L-25a, breaker #5 (MCC-1)
    • On a loss of power to the controller, all CVs will fail closed
    • They do not re-open on a return of power
  35. How many MW is 100% turbine load?
    869MW
  36. DEH operator auto mode
    • Control signals go through DPU 3/53
    • Auto tracks manual, manual tracks auto for a bumpless transfer
    • Speed control (rolling up the turbine)
    • -operator auto will not allow selection of a RPM value in the critical range of the turbine
    • Load control (power operations)
    • -automatically selected when the generator output breaker is closed
  37. What causes DEH to transfer from auto to manual?
    • Loss of power to operator auto
    • Failure of the speed feedback channel during contol mode
    • Operator auto DPUs fail to update the highway
    • 2 governor valves >3% from each other
  38. What are the positions for the main generator voltage regulator switch in the control room?
    • OFF
    • -DC adjuster is used
    • TEST
    • -DC adjuster is used
    • -AC circuits are energized
    • ON
    • -AC adjuster is controlling
    • -DC adjuster tracks the AC adjuster
  39. Main generator voltage regulator
    Controls the field strength of the exciter to maintain the generators voltage output constant at its setpoint (nomally 22Kv) if in auto.
  40. Normal EHC pressure
    1900-2100 psig
  41. Main generator protective relaying reverse power (332)
    • 332 relay senses direction of generator power flow
    • Trips the 386C relay during low power
    • -primary concern is turbine overheating due to no steam flow
  42. Consequences of high humidity on the main generator?
    • Will reduce the heat removal capability of the generator and increase windage heating (increased friction)
    • High moisture content can cause damage to the insulation of the stator and rotor windings
    • Moisture present in a high voltage electrical field may cause arcing
  43. Main generator protective relaying overall unit differential (487U)
    • Protects the generator, main transformer, and isophase bus to station power transformers
    • Trips the 386B generator trip lockout relay
  44. EHC pump power supplies
    • P-19A
    • -MCC-3
    • P-19B
    • -MCC-4
  45. What is the purpose/design of the permanent magnet generator?
    • Provides power to the voltage regulator, which in turn controls the stationary field of the AC exciter
    • -series of permanent magnets mounted on a rotating shaft
    • -conductors wound on a stationary segment
    • As the shaft rotates, an AC voltage is produced
    • -AC powers the voltage regulator and provides power to be amplified/rectified for the generator field excitation
  46. What is the purpose of the main turbine auxiliary governor trip solenoid valves (20-1/AG and 20-2/AG)?
    • Provides overspeed protection (103%)
    • -closes governor and intercept valves
    • -reopens them when the overspeed condition clears

    NOT A TURBINE TRIP
  47. What must be done if during synchronization, the generator has not picked up atleast 20MW?
    Use the DEH system to adjust load as needed to prevent a reverse power trip
  48. Voltage balance relay (360)
    • Prevents unnecessary trips due to blown fuses on the voltage sensing network
    • -relay is looking at the input to the voltage regulator, and to the metering/relaying
    • Also provides an alarm for loss of potential to the voltage regulator, generator metering and relaying
    • If both sides (360A and B dropped) control swaps to the DC adjuster (AC adjuster will trip)
  49. What automatically happens on a turbine trip?
    • Rx trip if > 15% reactor power
    • Main stop, governor, reheat stop, and combined intercept valves close
    • Cooling tower fans trip
    • ADVs and/or TBV opens on on program
    • Feedwater FIC-0701/0703 transfer to manual, MFPs rampdown to 5% flow
  50. Main generator AC adjuster
    • Senses main generator terminal voltage (AC) and compares it to an adjustable reference signal
    • -an error signal is sent to the trinistat power unit to control excitation such that a constant terminal voltage is maintained
    • When the AC regulator is in service, the DC adjuster has no control over voltage, but its signal is still present if the auto circuit fails
    • Powered from D-11-2
  51. What is the auto start feature associated with the EHC pumps?
    • The standby pump will autostart on low system pressure of 1750 psig
    • -this is high enough to ensure continued turbine operation (prevents turbine valves from drifting close as pressure decays)
    • Pump will run until it is stopped manually
  52. Main generator protective relaying, generator differential (387)
    • Current in each phase on each side of the machine is compared, any difference causes the 387 relay to actuate
    • Trips the unit on 386P lockout relay
  53. When do the main turbine bearing alarms alarm?
    • Alarms at 210oF
    • Normal temperatures for journal and thrust bearings should not exceed 185oF
  54. What happens on an actuation of the 386C coastdown relay?
    • Turbine trip
    • Fast transfer
    • Generator breakers open
    • B/U transfer trip
    • Exciter trip (field breaker opens)
  55. What is the purpose/design of the main generator exciter?
    • 3 phase AC generator whose output (500VAC at 400Hz) 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
    • -this magnetic field, combined with relative motion to the conductor bars produces a voltage
  56. What are the precautions for transferring the voltage regulator from TEST to ON or ON to TEST?
    • The regulator balance meter shall be adjusted to zero prior to the transfer
    • Should voltage or VARS change radically when transferring from ON to TEST, the voltage regulator control switch shall be immediately placed back to ON and the regulator balance meter shall be readjusted to zero before attempting to transfer again
  57. What does the main generator trinistat power unit do?
    It provides adjustable DC voltage to the exciter field windings
  58. What are the effects of a generator loss of field?
    • On total loss of field
    • -unit will trip
    • Can also lose synchronization with the grid
  59. What is the effect of insufficient service water flow to the EHC system?
    • Can result in erratic turbine valve operation
    • Normally maintain EHC fluid at 110-130oF (125-130oF preferred)
  60. What are the consequences of operating with main generator high hot gas temperatures?
    • Generator damage can occur due to overheating
    • -reduces life of the insulation
    • PPC alarms at 8oC hot gas delta T
    • Could be caused by high amount of localized heating or flow blockage of hydrogen
  61. What are the consequences of not derating when any phase of the rectifier indicates 2 blown fuses?
    • May cause an imbalance of diode output (amps per diode)
    • More fuses would blow, leading to a cascade effect
    • Once current imbalance is high enough, many more fuses would blow and the generator would trip on a loss of field
    • 40 diodes per phase
  62. What is the effect of a loss of H2 to the main generator?
    • The generator would overheat
    • The generator must be S/D and depressurized to <2 psig if the H2 leak cannot be stopped
  63. What does the main generator regulator balance meter do?
    • Indicates the difference between DC and AC adjuster outputs
    • Automatically maintained near zero (DC adjuster tracks the AC adjuster output) via the regulator "following" circuits for a bumpless transfer between auto and manual
  64. What does the OPC keyswitch on the DEH operator console do?
    • OPC test
    • -governor valves and intercept valves close (if the turbine is latched and the generator output breakers are open)
    • Normal
    • -allows operation of the OPC
    • OPC disable
    • -inhibits the OPC function (used for testing the 110% mechanical overspeed trip)
  65. What does actuation of the 386P relay cause?
    • Turbine trip
    • Fast transfer of electrical power to off site power
    • Generator breakers trip
    • Backup transfer trip
    • Exciter trip (field breaker opens)
  66. What brings in the main turbine trip alarm/turbine trip light on the DEH operator console?
    Auto stop oil pressure of <45 psig
  67. What does the generator neutral overvoltage relay (359N) do?
    • Limits current caused by ground faults
    • Detects faults for 96% fo the windings in the generator
    • -trips the 386P lockout relay
  68. How does the DEH UPS operate?
    • Normal mode
    • -automatically swaps to battery mode if A/C falls out of specification or fails
    • --auto swaps back to plant A/C
    • Battery mode
    • -converts DC to AC
    • Bypass mode
    • -powered directly from the lighting panel
  69. What are the DEH power supplies?
    • 2 trains of power from LCC-14
    • -panel L-81, panel L-83
    • If primary power fails, it immediately switches over to the seconday power (power seeking)
  70. At what value of condenser vacuum does the main turbine trip?
    18-21" Hg
  71. At what lube oil pressure does the main turbine trip?
    5-7 psig
  72. When does the main turbine trip on overspeed?
    110%
  73. What gives you a no load trip of the main turbine?
    < 8 psid for > 60 seconds across the HP turbine
  74. What are the limits on MSR outlet temperature during valve testing?
    • Control Reheater cooldown rate to less than 250oF.
    • -prevents undue thermal stress and possible distortion to the LP turbine stationary parts.

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