Systems Exam 4 - Main Turbine Flashcards
(33 cards)
Indication of a turbine runback in effect?
→ALB-6D Win 1.9 “ANY TURB RUNBACK EFFECTIVE” will be lit
→will not be lit if already below runback power setpoint
→for auto runbacks, the annunciator on Digital Control System (DCS) is illuminated for 9 minutes
Auto Runbacks
→HDP Trip: 35% per min to 800 MW (70%)
→MFP or Condensate Pump Trip: 35% per min to 700 MW (60%)
→C3 / C4: 200% per min for 1½ sec, then off for 28½ sec; repeat until condition clears
Manual Runbacks
→preset buttons available to drive turbine to selected MW load
→button provided for 50 MW @ 100 MW/Min; resets in 30 sec
→load settings available: 900 and 700 MW at 35% per min
→must be manually reset on DCS by turning OFF sub loop controller
→for manual runback or load reduction, Runback Annunciator clears once actual load reaches load setpoint
Where does MSR heating steam come from?
HP Stop and Control valves share common body; MSR heating steam taps off between the two valves.
How does the Main Turbine Turning Gear work?
Turning Gear is supplied from 2 valves:
→requires both valves to be open to initially roll the turbine
→speed varies between 80 and 190 rpm dependent upon whether vacuum established
→auto close if thrust bearing LO pressure 25#
→alarm actuated if EITHER valve is open AND <9 rpm on main turbine
→neither valve will open if generator breakers are closed
u-HV-6554A Turning Gear Valve #1:
→auto opens at 230 rpm decreasing
→auto closes at 260 rpm increasing
→manually operated <50 rpm due to lack on fine control at low speed
u-HV-6554B Turning Gear Valve #2:
→used to initially roll the turbine
→auto closes at 15 rpm increasing
→can be manually opened <15 rpm
Turbine Exhaust Hood Spray Valve
→solenoid valve opens at 194°F with >1340 rpm
→sprays condensate into the area to lower temps
→happens mostly at low power with low steam flow available to cool area
→condensate line taps off header before drain coolers
→solenoid valve must be manually closed once temp restored, but will auto close when high temp clears if LP turbine inlet steam pressure ≥7 psia
→separate MOV provided if solenoid valve insufficient to maintain temps
→if exhaust temp can’t be maintained <212°F, turbine is manually tripped
MTOT Temperature Control
Temperature in MTOT is maintained between 90°F and 100°F via heaters installed in the side of the tank.
Main Turbine Main Oil Pump
→located in HP turbine front pedestal
→driven by gear attached to HP turbine shaft
→provides all the lubrication needs of the Main Turbine / Main Generator once turbine reaches 1800 rpm
→during normal startup, Aux Lube Oil Pumps can be shut off around 1700 rpm because Main Oil Pump will have developed enough pressure
Main Turbine Aux Lube Oil Pumps
→3 pumps, A, B, & C
→powered from uB1, uB2, uB3
→A and B auto start at 110 psig
→C auto starts at 103 psig
→during normal startup, Aux Lube Oil Pumps can be shut off around 1700 rpm because Main Oil Pump will have developed enough pressure
Main Turbine DC Lube Oil Pump
→powered from uD2
→auto starts at 32 psig bearing header pressure
→only supplies bearings
Main Turbine Lube Oil Booster Pump
→used to prime the Main Lube Oil Pump
→turbine driven; supplied from main header
Main Turbine Shaft Lift Oil Pump (SLOP)
→auto starts at 510 rpm decreasing
→auto stops at 540 rpm increasing
Main Turbine Lube Oil Coolers
→3 lube oil coolers, 2 normally in service
→cooled by TPCW
→not normally shifted at power due to potential loss of lube oil and resulting Main Turbine damage
Shaft / Gland Seal Steam Systems
→initially supplied from Aux Steam; as turbine power increases, turbine becomes self-sealing at ≈40% turbine power
→Gland Steam supply header maintained at 4” WC via AOVs (supply and leakoff); valves fail as is on loss of air or power
→leakoff directed to FW Heaters 5 and 6
→leakoff header from Gland Seals and leakoff from stop and control valves is directed to Gland Steam Condenser
→Gland Steam exhaust uGS-0141, 0142 vented to PPV to ensure monitoring if SG tube leak
→opening the emergency bypass to atmosphere on either the Main or Auxiliary Gland Steam Condenser will result in an unmonitored release to atmosphere
EHC Pumps and Pressures
→3 dual stage pumps; stage 1 (LP) 114 psig, stage 2 & 3 (HP) 455 psig
→normally 2 pumps in service; standby pump auto starts at 398 discharge pressure
→powered from uB1, uB2, uB4
→red handswitches on CB-09
→114 psig control fluid supplies:
→Main Turbine Control
→tripping (protection)
→HP Stop Valve actuators
→455 psig control fluid supplies:
→LP Stop Valve actuators
→HP/LP Control Valves
EHC Operating Temperatures
→EHC fluid maintained at 131°F ± 9°F to maintain constant viscosity for proper operation of turbine valves
→minimum 70°F for starting EHC pumps
→Fyrquel is used because of its high flashpoint (475°F)
EHC Control Fluid Pressure, Function
→114 psig fluid directed to Startup Fluid Solenoids, Trip Block Valve and EHC Converter
→used to control the overall hydraulic system.
EHC Startup Fluid Pressure, Function
→114 psig fluid supplied from the Startup Fluid Solenoids and directed to Test Valves, which are used to stroke test stop and control valves
→essentially used to reset the system for power operation.
EHC Trip Fluid Pressure, Function
→114 psig fluid supplied from the Trip Block Valve and directed to the EHC Converter, Test Valves, Reset Valve, Trip Test Valves and HP/LP Stop Valves
→used to open the HP stop valves and is the source for Secondary Fluid.
→Trip Fluid also ports 445 psig fluid to open the LP Stop valves
EHC Secondary Fluid Pressure, Function
→114 psig fluid coming from the EHC Converter and supplied to HP and LP Control Valves
→used to control the HP and LP Control Valves by porting 455 psig fluid to actually operate the valves
Electro-Hydraulic (EHC) Converter
converts electronic control signal from the controller to hydraulic pressure and amplifies the pressure before sending it to the control valves
Digital Control System Load Rejection Feature
→designed to prevent overspeed of turbine in event of load rejection
→initiated by:
→any power level, load rejection >290MWe per second
→lower loads, IF actual load drops below 160MWe, AND actual load is 160 Mwe lower than load target
→when circuit initiated, EHC will transfer from load control to speed control
→speed control setpoint automatically set to value ≈ current actual load
→reset C-7 as required once desired load is reached to prevent instrument failure from causing spurious steam dump actuation
What do the HP and LP Stop and Control Valves do on a Turbine Trip?
Valves close to prevent overspeeding of the turbine.
LP Control Valves only throttle down on large loss of electrical load to help overspeeding of the Main Turbine.
Note: during normal operation at power, HP & LP Stop Valves are normally open with LP Control Valves fully open and HP Control Valves 50% open.
Main Turbine Speed Signal Probes
→total of 8 speed probes (6 used, 2 installed spares)
→3 probes provide input to software overspeed
→3 probes provide input to hardware overspeed
→each of the six speed channels (3 for hardware overspeed, 3 for the software overspeed) is automatically tested once every 24 hours when turbine >40 rpm
→tests verify that speed channels trip when speed is simulated >1980 rpm
