Main Generator & Controls Flashcards
State the Main Generator Ratings.
1200 MVA 1080 MW @ 0.85 PF,
22 KV,
10% Step Change,
5%/min Ramp from 15-100%
Brushless Excitation System.
PMG uses Rotating Magnets to generate AC output.
This passes thru the Field Exciter Breaker, goes to the SCR’s, which convert AC to DC and the Trinistat Firing Circuits which are controlled by the Voltage Regulators (Auto / Manual).
This becomes the Exciter Field Current (DC) which is provided to the Exciter Stationary Field.
The Brushless Exciter generates an AC output in the Rotor Exciter Windings which is sent to the Exciter Rectifiers.
The Rotating Rectifier Assembly converts AC to DC, and sends this DC thru the Rotor Shaft, to become the Rotating Magnetic Field of the Main Generator.
The MG produces an AC output from the Stationary Windings through the MG Leads, via the Isophase Bus, to the Main and Aux X-formers.
Discuss the Permanent Magnet Generator (PMG).
Mounted on the end of the Exciter Shaft, Rotating Permanent Magnets and a Stationary Stator
Alternate Power for DEH Computer when Turbine > 600 RPM (Normal power is Vital SUPS)
Discuss the Exciter.
Placed in service at 1800 RPM just before placing the Generator on-line.
What are the Exciter Breaker trips?
(“PSIG”)
Primary Lockout Main Generator
Secondary Lockout
Instantaneous Current Limit #3 Trip
Generator Over-Excitation Protection (OXP)
Discuss the Power Amplifier.
Converts PMG AC output to variable width DC pulses by the use of pulse fired SCR’s
Output is overlapping DC from three phases of PMG which gives near ripple free DC output.
Discuss Excitation Switchgear.
Contains a “Power Seeking” ABT normally aligned to “C” Battery Bus and Auto Transfers to the “D” Battery Bus if power is lost. Manually transfer by taking the toggle switch to Test position.
Discuss AUTO (Automatic Control) Voltage Regulator.
AC VR controls the magnetic field in Main Generator rotor to maintain Main Generator output voltage at the demand setting of the AC voltage adjuster (To raise MVARs OUT – raise AC VR setting. “Voltage is VARS”)
If the Field Voltage raised with Generator offline, Main Generator Terminal Voltage will increase
Limiters are in service to control parameters within limits automatically
Discuss Manual (Direct Control) Voltage Regulator.
Normal power “C” 125 VDC, Emergency power “D” 125 VDC
DC VR maintains a constant current to MG rotor at demand setting of the DC regulator adjuster
NO automatic limiting protective functions; only protection is generator trips via Lockouts
No Load Excitation is 14%, Max Excitation is 17%
Discuss the Three Position Voltage Regulator Switch.
OFF - DC VR (Manual) – Green Light
TEST - DC VR (Manual), used to adjust AC VR-bump less transfer (Null Meter) - Amber Light
ON - AC VR (Auto) – Red Light
Discuss the Power System Stabilizer.
Provides damping of the electro-mechanical oscillations that occur as a result of system disturbances
Only functions with AC regulator on. Does not work with the DC regulator
Placed in service IAW GOP-201 (45%), Removed from service IAW GOP-123 (45%)
Automatically removed from service <20% power (current flow), AC Regulator turned off or Generator Output Breakers open
Must notify System Dispatcher within 30 minutes of a change in the status of the PSS
PSS ON Permissive:
Generator Output Breaker closed
AC Regulator ON
> 20% power (current flow)
Discuss the Null Meter.
Measures the difference between AC and DC Voltage Regulators input to Firing circuit and used to match AC VR output to DC VR output for bump-less transfer.
Discuss the Adjuster Follower.
When the voltage regulator is in automatic (ON), the DC adjuster follower circuit insures that the DC regulator constantly tracks the AC regulator so that there will be a bump-less transfer in machine voltage and reactive loading should the AC regulator be switched off for any reason. The DC adjuster follower circuit is only in service when the AC voltage regulator is in the ON position
Discuss Under excitation Protection.
Minimum Excitation Limiter (MEL) – prevents AC VR decreasing excitation below curve
Loss of Field Trip (backup for MEL)
Discuss Over excitation Protection.
MXL – 105% of rated field current (limits AC VR only)
OXP – 110% of rated field current 3 relays with time delays:
1-Removes the follower circuit and takes DC VR to preset position
2-switches to DC VR
3-primary lockout (110% for 5 seconds)
Instantaneous Current Limiter – 3 relays:
1-limits AC VR – 100%
2-limits AC&DC VR – 105%
3-Trip via Primary Lockout – 110%
Volt/Hz Limiter – prevent oversat due to Hz decreasing, 3 relays:
1-106%-decreases AC VR
2-110%-45 sec trip
3-118%-2 sec trip
Off-Line Forcing – prevents off-line overexcitation–105%-disconnects AC & DC raise switches
What protections are available when the Direct Control Voltage Regulator (DC VR) is in service?
(“IVLO”):
o Instantaneous Current Limiter
o Volt/Hz Limiter
o Loss of Field Trip
o OXP
Discuss Loss of Transducer (voltage regulator).
1 or #3 – forced to DC VR
#2 – forced to AC VR
Discuss Under-Frequency Protection (86UF).
There are four relays (for redundancy) on the back of RTGB 101(201) which will open the generator output breakers ONLY, on under frequency of <58 [57] Hz.
Discuss Inadvertent Energization Relay (86INAD).
Protects Main Generator from being energized as an induction motor
The relay will trip if an attempt is made to close either of the Main Generator Breakers while there is ‘0’ voltage measured on any phase within the Main Generator. Also tripped are the 6900 VAC and 4160 VAC feeder breakers from the Auxiliary Transformers.
What cools the Main Generator?
Hydrogen cools the Stator and Main Generator Bushings, (cooled by TCW) ~75 psig
Forced Air cools the Exciter and Isophase Buses, (cooled by TCW)
Discuss Isophase Bus Duct cooling.
Self Cooled Mode (Fans failed) capable of 60% power
Normally cooled by two fans (1-run, 1-stby) with air cooled by TCW
Monitor Power, Amps, and Temperatures
Trip at 125C
Discuss Main Generator Auto Ground Detection.
One brush on Main Generator shaft and one brush on Main Generator rotor windings
Alarm and indicating lights if insulation breaks down between rotor windings and MG shaft
Discuss Isophase Hydrogen Detection.
Air sample is burned (catalytic) which varies temp of detector resulting in Resistance change as H2 changes. This changes volts in a bridge circuit. Volt change drives meter circuit and Alarm/Protection.
At 1.6% Hydrogen a damper will shift to allow fans to purge the Isophase Bus Ducts with Outside Air.
What happens at 1.6% H2 concentration in the Isophase Bus Ducts?
A damper will shift to allow fans to purge the Isophase Bus Ducts with Outside Air.
Discuss Digital Fault Recorder.
Continuously monitors various Main Generator parameters.
What is normal Main Generator Hydrogen purity?
Maintained greater than 90% Hydrogen.
Discuss Generator Condition Monitor.
Detects overheating by sensing thermal decomposition of insulation
Hydrogen Gas passes through Ion Chamber with a coated radioactive wire. Contaminants from overheating will interrupt the flow of charged particles emitted by wire. Decrease in current actuates alarm located behind the RTGB. 80% of scale is Normal, will alarm if drops to 50%
To check if alarm is valid: Send Operator to check computer.
Discuss Main Generator Temperature Monitoring.
Generator Cold Gas temperature (4 RTD’s)
Normally 38 C
If ≥ 46 C Throttle TCW to maintain < 46 C
If ≥ 47.7 C Reduce MG MVAR Loading to 0 MVAR
If ≥ 50.7 C Rapid Downpower to reduce generator load
Hot Gas (24 RTD’s) – Trip Rx/Turbine if ≥ 113 C
Discuss Trip of Generator Output Breakers 8W49 & 8W52.
Does not immediately trip the Turbine. The OPC tries to close down on the GV’s & IV’s to handle loss of load. When plant trips, no FDBT to the SUTs The Fast Transfer must take place within 3 to 10 cycles, if not there is a Lockout. Turbine has already coasted down so that Frequency is significantly reduced.
Discuss Generator Trip accomplished via Generator Primary / Secondary Lockout Relay.
Trips open Switchyard Mid and East Breakers
Trips Generator Field Breaker
Trips Auxiliary Transformer supply breakers (Fast Dead Bus transfer of In-House Loads)
20/ET and 20/AST Solenoids energize to trip turbine (steam admission valves close)
Closes Startup Transformer supply breakers
Discuss Generator Secondary Lockout Relay 86GB.
Generator Field Failure
Generator Leads Ground
Generator-Transformer Delta Current
Generator Breaker Failure
Generator Turbine Trip
Aux Transformer Breaker Failure
Aux Transformer Sudden Pressure Trip
What are the Generator Trips Actuated By Primary Lockout Relay 86GP?
Generator Negative Sequence,
Protects generator from external faults. Unbalanced switchyard or un-isolated fault can produce a negative phase sequence that results in local overheating, insulation damage, and uneven torque on the Main Generator Rotor. A valid alarm is at least 1900 Amps difference between phases trips generator if a very high negative phase current, (63%) The larger the imbalance the less time allowed. [Timer on Bench section energizes starts count down to Turbine Trip]
Generator Differential Current,
Checks current in/out, protects phase to phase shorts/grounds
Generator Ground, Detects Phase to Ground Faults in, Stator Windings, Isophase Bus and Primary side of the Main and Auxiliary Transformers
Generator Leads B/U Trip,
Protects against a fault on the MG output leads to the Main Transformer
Generator Turbine Trip,
If output bkr or excitation bkr closed, and all 4 Throttle Valves go closed OR if Auto-Stop Oil Pressure is Low
Generator String Bus Differential Current,
Protects against fault on distribution lines, MG to swyd
[Generator Motoring],
relays sense Reverse Power
[Generator out of Step]
Main Transformer Differential Current in/out of Transformer
Aux Transformer Differential Current in/out of Transformer
Excitation Switchgear Trip, OXP, Logic P/S Failure, and Instantaneous Current Limiter
Volts/Hz Protective Trip, Gives a lockout if there is a fault on the Midway lines that is not removed
What are the Main Generator Capability Curve Regions and what is the primary concern in each region?
Region 1: Rotor Windings
Region 2: Stator Windings
Region 3: Stator Core
Region 4: Slip a Pole
Discuss Main Generator Startup and Paralleling to Grid.
Generator Ground Check
Close Exciter Field Breaker
Raise MG Terminal Voltage to 22 KVA with the DC regulator (adjuster)
VR to TEST – Adjust AC VR to zero out VR Null Meter – Take VR to ON
Insert Synch Plug in and turn to AUTO 1E (preferred) or 1M
Match Incoming and Running voltages - Push the DEH AUTO SYNCH PB
Depress and Hold the SYNCH ENABLE [AUTO SYNCH MANUAL PERMISSIVE] PB as needle approaches 11 O’clock, Release PB when the breaker closes or needle passes 12 O’clock
There is a 5 Second Dropout Timer that defeats the Auto Sync Manual Permissive Pushbutton if it is held for a Full Revolution of the Syncroscope
Pick up 40 MW load minimum
Select and close the remaining Main Generator breaker in Manual
Remove Synch Plug and match breaker flag to actual position
Discuss Main Generator Shutdown.
1[2]-GOP-123, “Turbine Shutdown -Full Load to Zero Load”
Removing the Generator from service
If unit is being shutdown for refueling or the reactor is to be shutdown then: Reduce turbine loading to 25% and transfer station electrical 6.9KV loads from AT’s to the ST’s Trip the reactor. Verify generator lockout transfers both the A2 & B2 4.16KV buses. Complete 1[2] EOP-01 & 02. Take the Voltage Regulator Control Switch is then taken to OFF. Take the AC Regulator Adjuster is adjusted to minimum output. Take the DC Regulator Adjuster is adjusted to minimum output.
If reactor is to remain critical, or if unit is being shutdown for a SG tube leak then:
Turbine load is reduced to 0 MWs
MVARS are reduced to 0 by lowering on the AC Regulator.
When Generator output reaches 20 MW: Open Both generator breakers (East and Mid) Trip Turbine Open Exciter Field Supply breaker Place Voltage Regulator Control Switch in OFF. Take the AC Regulator Adjuster to minimum output. Take the DC Regulator Adjuster to minimum output.
Contact Load Dispatcher to open disconnects if Main Generator offline > 4 hours
