Turbine Controls Flashcards
What are the purposes of the reheat intercept and stop valves?
Intercept valves (closest to turbine) limits flow of steam from MSR after load rejection or overspeed.
Stop valves provide fast additional protection to prevent turbine overspeed in event of trip
Describe operation of the turbine throttle/governor valves and arrangement.
Governor valves 2 and 3 open together first, then Gov valve 1 and gov valve 4 last and is throttled to control header pressure.
What is the purpose of autostop oil, where is it normally supplied from and what is its backup supply?
Autostop oil controls the trip functions of the main turbine and holds HPO-65 (interface valve) closed against spring pressure until a trip condition is sensed where the oil will drain off and trip the main turbine.
Normally supplied from P-18 with P-21 being the backup.
What is the double shocker?
Steam flow to the HPT with 1 and 3 GVs only open or 2 and 4 only open. Can lead to damage on HPT.
How does the emergency trip block operate and what trips are generated from the trip block?
The trip block is mounted on a pivot bar. When trip occured the block pivots and allows autostop oil the be dumped and trip the turbine.
Trip Block Trips
- Thrust Bearing (75#)
- Low Vacuum (24.5” Hg)
- Low Bearing Oil Pressure (6 psig)
- Turb Trip Solenoid (Gen LO, DROPs, Rx Trip, both MFP Trip, EHC loss of power, etc)
What function does the overspeed trip mechanical dump valve serve for trips on the trip block?
Serves as a seal in for trips on the trip block by staying open.
What are the turbine lube oil pumps, functions and autostarts?
P-19 (Backup LO Pump) - Provides lube oil when turbine not running. Powered by B-11 and autostarts at 10-12#.
P-20 (Emergency Lube oil Pump) - Provides assured oil source for turbine. Powered by B-56, autostarts at 8-10 psig.
P-21 (Seal Oil BU Pump) - Provides backup Seal Oil and autostop oil. Powered by B-56 it autostarts at 10-12#.
P-76 (HP Lift Oil Pump) - Needs P-19 or P-20 to provide suction. Provides lift oil pressure to bearings 3,4,5,6. Autostarts < 600 rpm if B.O. > 7#. Stops if oil pressure < 2.5#.
What provides an electrical backup trip to HPO-65 (Trip interface valve)
SV-8527 is energized on loss of autostop oil pressure (2 of 3) which will bleed off EH oil to provide trip function.
What components does the OPC circuit control and how is this accomplished?
OPC will close the governor and intercept valves by opening SV-8525 and SV-8526 on the EH oil system at > 103% turbine speed or generator output breakers open and load rejection.
> 30% difference between megawatts and the reheat pressure with the generator breakers open, the intercept and governor valves close to maintain 1800 rpm and shifts turbine to operator auto.
Describe the Electronic Overspeed System.
EOS function is to trip main turbine during overspeed condition (1980 rpm or 110%) from main speed probe independent of the mechanical overspeed trip device.
It contains 3 channels (A,B,C) powered from D-11,D-21 and D-46 respectively. When K1 and K2 (interposing relays) de-energized (2 of 3 channels tripped), the K1/K2 contacts close to energize R1 or R2 trip relays which opens SV-8524, SV-6623 and 6624 (Backup Trip Solenoids) to depressurize autostop system.
Both Interposing relays must be de-energized and either output relay have to be energized.
What would be the effect of de-energizing A and B EOS channels?
Unable to trip on an electronic overspeed condition since the K-1/K-2 contacts must be energized for trip function.
What are the power sources for EH control system?
RC-1/Y01
What determines whether turbine is in speed or load control? What changes when control is swapped?
Generator Output Breakers
Display will change from RPM to a voltage signal
What valves are controlling when turbine is latched in speed control and raising speed to sync turbine to grid? When is control swapped to governor valves?
Turbine is initially controlled by throttle valves with Governor valves open. This is referred to full arc admission which evenly warms up the turbine and casing. In this mode the throttle valves are in proportional control with governor prop/int control with 80 rpm speed error.
At 1700 RPM turbine is shifted to governor valve control (TV-GV Transfer). Gov valves are swapped to proportional control and 100 rpm bias given to throttle valves.
Speed is then raised to 1800 RPM to sync to grid.
What occurs with the turbine when Gen Output Breakers are closed?
Turbine BLOCK loads approximately 40 MW and reverts to manual to provide bumpless transfer and then back to Op Auto.
What do the aux speed channel and main speed channels supply?
Main: reference feedback to turbine control and overspeed trip circuits (110%)
Aux: Turbine shaft speed ind on C01, and signal to OPC
