Main Turbine Control, EHC/DEH

Question 1

What is the purpose of the EHC system?

Answer 1

Provides hydraulic fluid for the operation of the main stop valves, governor valves, reheat stop valves, and intercept valves.

Question 2

What are the power supplies for the EHC pumps?

Answer 2

P-19A - MCC-3

P-19B - MCC-4

Question 3

What is the normal lineup for the EHC pumps?

Answer 3

1 pump running, 1 in standby

Question 4

What causes an EHC pump to auto start?

Answer 4

Standby pump auto starts at 1750 psig

Question 5

What happens on an EHC reservoir low-low level?

Answer 5

At 7 5/8” from the bottom of the tank, standby pump gets locked out, but the running pump stays running.

Question 6

How does a loss of service water affect the operation of the EHC system?

Answer 6

Non-Critical Service Water cools EHC fluid, so EHC would heat up, causing erratic control of the governor valves

Question 7

What happens when the turbine is latched?

Answer 7

• Performed at the front standard
• Auto stop oil (supplied by main lube oil) pressure builds up, which closes the interface valve
• With the interface valve closed, EHC pressure builds up to allow opening of the main stop, governor, reheat stop, and intercept valves.

Question 8

How do the 20ET trips trip the turbine?

Answer 8

Port EHC around the interface valve, causing all steam admission valves to close

Question 9

How do the interface valve trips trip the turbine?

Answer 9

Auto stop oil is dumped, causing the interface valve to go open, which causes EHC to go back to the reservoir and steam admission valves go closed

Question 10

What are the 20ET turbine trips?

Answer 10

• MSIV out of position
• Thrust bearing - 40 mils
• Low auto stop oil pressure - 45 psig (2/3 logic)
• ATWS (2375 psia PCS pressure 2/4 logic)

Question 11

What are the interface valve turbine trips?

Answer 11

• Manual trip lever
• Overspeed - 110%
• Low condenser vacuum - 18-21” Hg
• Low lube oil pressure 5-7 psig
• Solenoid trips

Question 12

What are the solenoid turbine trips?

Answer 12

• Reactor trip
• Generator trip
• MSIV out of position
• C-01 pushbutton
• No load - < 8 psid across the HP turbine for > 60 seconds
• DEH initiated (loss of power to the manual cabinet)

Question 13

What is the purpose/function of the Aux Governor Trips

Answer 13

At 103% rated speed, governor and intercept valves go closed. Once speed is below 103%, valves go back open.

Question 14

What causes DEH to swap to manual control?

Answer 14

• Loss of power to auto controller
• Auto controller not updating the Data Highway
• Greater than 3% deviation between governor valves
• Loss of speed feedback loop while in Auto Speed Control

Question 15

What are the limitations on journal and thrust bearing temperatures?

Answer 15

Should not exceed 185 F to prevent damaging bearing surfaces

Question 16

What are the limitations on turbine exhaust temperature?

Answer 16

Should not exceed 217 F for extended operation, or 250 F for > 15 minutes to prevent overheating the later stages of the LP turbine

Question 17

What is the precaution for relamping the LATCH pushbutton on the DEH panel?

Answer 17

Shall not be relamped online due to possible turbine trip

Question 18

What are the required parameters to sync to the grid?

Answer 18

• Reactor power <= 13%
• Tave <= 540 F
• TBV controller output signal > 55%

Question 19

What is the preferred response to “Turbine No Load Pretrip” alarm?

Answer 19

Turbine will trip after 60 seconds, so it is preferred to manually trip the turbine