DEHC Flashcards
DEHC Generates electronic signals to position which components:
a) four HP turbine stop throttle valves
b) four HP turbine governor-control valves
c) two reheat stop valves and two intercept valves per LP turbine
Trips the turbine if speed exceed____ of rated speed to prevent exceeding ______.
108%
120%
What are the 4 headers?
Emergency trip header
HP supply header
Normal drain header
Atmospheric drain header
If one input of three fails, _____.
The average of the other two is used to control the turbine.
Reactor trip occurs above _____ when <______ psig on _____ 1/2 trains -or-
_____closed
P-8
<1000 psig
2/3 on 1/2 trains
4/4 TVs closed
OTdeltaT/OPdeltaT runback
In auto:
In manual:
How actuated:
When does it stop?
Ramps down at 200%/minute for 1.5 seconds, rests for 28.5 sec, repeat until condition clears or 235 MW reached.
2/4 delta T channels within 3 % of setpoint.
CD/FW PP trip runback
In auto:
In manual:
How actuated:
If in operator Auto:
Ramps down at 250 MW/min, stops at 700 MW.
If in manual:
Ramps down at 200%/min, stops at 700 MW.
Actuated manually at OWS or with runback PB.
HD PP trip runback:
In auto:
In manual:
How actuated:
In auto: Ramps down at 20 MW/min, stops at 780 MW.
In manual: Ramps down at 200%/min, stops at 780 MW.
Actuated manually at OWS.
FW heater isol runback:
In auto:
In manual:
How actuated:
In auto: ramps down at 100 MW/min, stops at 1050 MW.
In manual: ramps down at 200%/min, stops at 1050 MW.
Actuated manually at OWS.
Single valve control mode.
What does it do?
When used?
Advantages/disadvantages
- All GVs act as one, opening/closing together.
- Used: -<20% power - TV/GV testing -If GV demanded position differs substantially from actual position
- Single admits steam to full arc of HP turbine: more even heating, minimizes thermal stresses, less efficient due to throttling losses.
Sequential valve control mode.
What does it do?
When used?
Advantages/disadvantages
- GV-1, 2 and 3 open together, then GV-4 throttles to control turbine speed after GV 1-3 are full open.
- Used >20% power
- Provides greater efficiency due to less throttling losses.
Operator Automatic/Overspeed Protection Control Controller (OA/OPC) provided trips:
- Overspeed 2/3 >=108%
- EH pressure low 1000 psig
- Watchdog trips: loss of drops 3 and 53 or signal from ETS to OA to generate turbine trip.
ETS controller provided trips:
- Overspeed 2/3 speed >=108%
- Bearing oil pressure low 6 psig
- Condenser low vacuum 10” Hg absolute, can be bypassed to allow turbine to latch without vacuum
- Thrust bearing failure 70 psig
- Watchdog trips, loss of both drop 2 and 52 or signal from OA to trip turbine.
Valve contingency:
____error between GV demand and actual position or ___seconds on 2/2 LVDTs.
On1 GV: ________
On 2 or more GV:__________
5% error between GV demand and actual position or >10 seconds on 2/2 LVDTs.
On1 GV: reject to single valve control
On 2 or more GV: reject to manual
OPC 1 and 2 solenoids are powered from _____. Function is to ______.
Strokes ____ and _____ only.
Prevents ____________.
DC bus 114
Strokes GV and IV only
Prevents turbine overspeed on partial or complete load rejections. Actuates at 103%.
Standby auto EH pump starts at ___
1600#
EH is cooled by ____ and maintains temperature of EH fluid ____ to _____.
WS
110-130F
There are ____ ETS trip manifold solenoid valves and they are (energize/de-energize) to trip.
8
De-energize
What are the 4 feedback loop modes?
Speed/frequency
MW
Impulse
NIS power
EH 5042 directs air to isolate the following three components:
- AO check valves (non-return) close
- ES062s (MSR 1st stage) close
- Spillover valves open
Resonance region for main turbine is ____ to _____ RPM.
800-1200
C-20 AMS permissive
Inputs
Function
2/2 impulse pressure >30%
Arms AMS
P-13 turbine at power
Setpoint and coincidence
Function
1/2 P-imp ch >10%
2/2 P-imp ch <10% to clear
Input to P-7 permissive
C-5 turbine low power rod stop
Setpoint and coincidence
Function
Turbine low power rod stop
Validated P-imp <15%
Stops outward rod motion in auto
Speed feedback loop maintain speed at ______. ___ speed sensors fail, kicks to manual. Auto enabled when ______.
1800+-2 rpm
2/3
1/2 output breakers closed
Impulse feedback loop quickly adjusts_____ position to match actual and reference pressure.
GV
MW feedback loop adjust _____to match actual and reference MW.
MW (in/out) selected when w/i ___ of any power limit to prevent a power increase above limit.
GV position
MW out
5%
Any runback in progress or runback pushbutton depressed will_____.
disable the GO pushbutton.
CD/FW runback is unique because ______
Can be initiated from pm02j
When OPC actuates, what happens?
4 items
a) OPC solenoid valves 20-1/OPC and 20-2/OPC energize to open
b) OPC header is depressurized to Atmospheric Drain Header
c) EH pressure is released from GV and IV dump valves allowing spring pressure to close valves
d) Steam ventilating valves _GS036A and _GS036B open when EH pressure is <1000 psig to bleed off steam between GVs and IVs (same as during turbine trip.)
After OPC actuates, When speed drops to <103%: (1854 rpm), what happens?
a) 20-1/OPC and 20-2/OPC deenergize and close
b) OPC header is repressurized and IVs are allowed to reopen
c) GVs will reopen to maintain rated speed (Operator Automatic)
Low condenser vacuum alarm is ___
Low condenser vacuum trip is ____
Alarm is 22.5” Hg
Trip is 20” Hg
The condenser trip override bypass is automatically disabled above ____ rpm.
250 RPM
The EH reservoir Lo-2 lockout is reset with a switch located _____.
MCB
Piping downstream of the ___ heating up is an indication that the filters are being bypassed. With the filters and coolers bypassed EH reservoir level will rise due to the fluid _____.
check valve
being hotter
Inputs to servo valves:
(1) Demand signals from DEHC
(2) Feedback signal from the valve LVDT demodulator
(a) Valve travel converted to a proportional AC signal
(b) AC converted to DC by the demodulator
(3) DEHC demand signal and LVDT feedback summed for control
Two actuation signals to RPS indicate the turbine is tripped
a) All four TV closed, or
b) 2/3 pressure switches in the EH fluid Trip Header < 1000 psig on 1/2 trains.
Electrical turbine trips from train A SSPS
1) K640 relay from Train A of SSPS
a) P-4
b) SI
c) P-14
2) Electrical Overspeed from Braun system– 108% of rated speed
3) Actuation of Turbine Generator Tripping Relay 86G1A
4) AMS
Electrical turbine trips from train B SSPS
1) K640 relay from Train B of SSPS
a) P-4
b) SI
c) P-14
2) Actuation of Turbine Generator Tripping Relay 86G1B
Local Emergency Trip Pushbutton trips turbine by ______.
Deenergizes all eight solenoid valves by removing power directly by in series contacts.
What is the valve speed in manual?
a. for GV LOWER NORMAL?
b. for GV LOWER FAST ACTION?
c. for GV LOWER RAPID?
a. 180 second valve stroke time
b. 45 second valve stroke time
c. 30 second valve stroke time
Once the transfer from TV to GV control has been made, can control be transferred back to the TV’s; and how or why not?
Cannot transfer control back to TV’s. Once control is transferred to the GV a FULL OPEN signal is applied to the TV servo actuators. This signal keeps the TV fully OPEN until the Turbine is tripped. Only means then is to trip turbine, and then relatch.
____ emergency trip header pressures and _____ turbine throttle valve closures required while in mode 1 with power ______.
3 >=910psig
4
>P-8
