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
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
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
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
What happens on an actuation of backup (386B) turbine generator lockout relay?
Limits AC adjuster from underexciting the generator
If terminal voltage drops low enough the plant will trip on underexcitation device 340
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
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
Impact of a loss of power to the DEH console?
Turbine trips if:
-both manual panel power supplies fail (24vdc)
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
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
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
Exciter protective device loss of field relay (340)
-short circuit in the generator field
-accidental exciter field breaker trip
Alarms and trips the plant (386P) on abnormally low or loss of field
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
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
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.
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.
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
What do the rectifier wheels do on the main generator?
Rectifies exciter AC current to DC current for the main generator field windings (rotor)
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
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
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
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
How many MW is 100% turbine load?
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
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
What are the positions for the main generator voltage regulator switch in the control room?
-DC adjuster is used
-DC adjuster is used
-AC circuits are energized
-AC adjuster is controlling
-DC adjuster tracks the AC adjuster
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.
Normal EHC pressure
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
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
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
EHC pump power supplies
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
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
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
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)
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
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
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
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
When do the main turbine bearing alarms alarm?
Alarms at 210oF
Normal temperatures for journal and thrust bearings should not exceed 185oF
What happens on an actuation of the 386C coastdown relay?
Generator breakers open
B/U transfer trip
Exciter trip (field breaker opens)
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
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
What does the main generator trinistat power unit do?
It provides adjustable DC voltage to the exciter field windings
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
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)
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
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
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
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
What does the OPC keyswitch on the DEH operator console do?
-governor valves and intercept valves close (if the turbine is latched and the generator output breakers are open)
-allows operation of the OPC
-inhibits the OPC function (used for testing the 110% mechanical overspeed trip)
What does actuation of the 386P relay cause?
Fast transfer of electrical power to off site power
Generator breakers trip
Backup transfer trip
Exciter trip (field breaker opens)
What brings in the main turbine trip alarm/turbine trip light on the DEH operator console?
Auto stop oil pressure of <45 psig
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
How does the DEH UPS operate?
-automatically swaps to battery mode if A/C falls out of specification or fails
--auto swaps back to plant A/C
-converts DC to AC
-powered directly from the lighting panel
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)
At what value of condenser vacuum does the main turbine trip?
At what lube oil pressure does the main turbine trip?
When does the main turbine trip on overspeed?
What gives you a no load trip of the main turbine?
< 8 psid for > 60 seconds across the HP turbine
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.