EHC: Electro-Hydraulic Control Flashcards
What valves are controlled by the EHC System?
Main Stop Valves
Control Valves
Control Intercept Valves
How many Main Turbine speed signals are used by the EHC System?
2
What happens if one of the speed signals used by the EHC System is lost?
Acceleration will double.
EHC uses both speed signals to get the acceleration indication. Losing one will cut indicated acceleration in half so the EHC System will double actual acceleration in an attempt to return indicated acceleration to its original value.
What happens if both speed signals to the EHC System are lost?
The Main Turbine will trip unless its < 100 RPM or in Standby
If the Main Turbine Output Breakers are closed, what is the only speed reference signal that can be selected on the EHC Control Panel on B06?
1800 RPM
How are the speed signals generated for the EHC System? How do they work?
- Magnetic Speed Sensors
- Sensors are located over a toothed wheel and generate a sinusoidal frequency proportional to Turbine speed. At 1800 RPM they output 4800Hz which is then converted to -10VDC for use by the EHC System.
What is the trip logic for Aux Speed Control in EHC?
2/3
What functions do the Aux Speed Control Units provide in the EHC System?
Backup Overspeed Trip at 111.5%
Permissive for MSLO Pressure Trip (100 psig) at 75% rated speed (1350 RPM)
Permissive for Loss of Both Speed Signals Trip at 5.5% rated speed (100 RPM)
When in Standby, what are the overspeed trip set points?
Normal - 110%
Backup - 105% - Backup lowered from its original value.
When a Load Rate (1/2, 1, 3, 10) is selected by an operator on the EHC Control Panel, when is this rate applicable: Increase, Decrease, or Both?
Increase ONLY
Decrease is always 130%/min
When is the INCREASE button on the EHC Control Panel inhibited?
- PLUB
- RPCB
- Anytime the Load Set Motor is adjusted any more than about 2% greater than the Load Limit Potentiometer. (i.e. you can’t completely move the Load Set Motor out of the way. It’ll stop at 2% above and follow the Pot down remaining 3.5%-4% above the Pot)
In addition to the INCREASE/DECREASE pushbuttons, what else can control the Load Set Motor?
- RPCB System - “Runback” on RPCB
- Lowering the Load Limit Pot
- Speed Matcher - not used
- PLUB - “Runback” generated but transparent because Turbine is tripped.
What trip of the Main Turbine is deactivated when in Standby?
Loss of Both Speed Signals
What has to be done with the controlling valve signals prior to entering Standby mode in EHC?
They should be matched. There’s a pushbutton to bypass this requirement that works going both ways.
What two types of tripping protection are available for the Main Turbine?
Mechanical (MTSV)
Electrical (ETSV)
Do Main Turbine Setback and Runback work while in Standby?
No
What happens when the DECREASE button for the Load Set Motor is depressed?
Load Set Motor output lowers 130%/min and Load Reference Signal goes with it (assuming it is below the Load Limit Pot)
What Load Rate is automatically selected when the first Main Generator Output Breaker is closed?
10%
How do you clear a Main Turbine Setback?
Lower the Load Limit Potentiometer until the Load Limiting Light comes on.
What is performed first: Shell Warming or Chest Warming?
Shell Warming
Chest Warming refers to what?
The warming of the valve chests
What do the INCREASE/DECREASE pushbuttons on the Chest/Shell Warming section of the EHC Control Panel operate?
MSV-2
When performing Chest Warming, which valves are open?
MSV-2 only.
Which Starting Rate is automatically selected when the Main Turbine is reset?
Slow
What must be done to the Standby Potentiometer before a reset of the Standby Circuit can be performed?
It has to be taken to zero.
When do the Intercept Stop Valves open?
When the Main Turbine is reset.
When is Stage Pressure Feedback used?
Control Valve Testing
What are the power supplies for the EHC System?
House Power - NNN-D15
PMG while > 90% speed
How is a PLUB generated?
Looks at MW vs. Hot Reheat Pressure. If MW go down rapidly in relation to Hot Reheat Pressure a PLUB is generated which will trip the turbine.
