Main Feedwater (FW/FT)

Question 1

What is the minimum and maximum speed for the Main Feedwater pump turbine?

Answer 1

• Min Speed: 4150 rpm
• Overspeed: 6350 rpm (110%)

Question 2

What is the steam source for the Main Feedwater pump turbines?

Answer 2

MFP Turbines (9 stages)
* < 35% power: Main Steam supplied (HP)
* > 35%: Hot Reheat (from MSR D) starts to supply (LP)
* Aux Steam can be manually aligned during outage for testing

Question 3

What are the Main Feedwater Pump trips?

Answer 3

**Trip Signals (Energized to trip)
1. Manual - MCR or Local
2. Overspeed > 6,350 RPM (110%)
3. Low Suction Pressure < 245 psig (2/3 logic) 10 sec TD for B MFP / 15 sec TD for A MFP. One MFP trips first to help prevent a complete loss of MFW on short secondary transients. (Alarms at < 290 psig)
4. High Discharge Pressure > 1780 psig (2/3 logic) (alarms at 1690 psig)
5. Low Main Condenser Vacuum > 13.5” HgA (2/2 logic) [PSs on MFP Turb Exh – Exhausts to Cond A]
6. Low Control Oil Pressure to Stop and Control Valve Operators < 75 psig (2/3 logic)
7. High Active & Inactive Thrust Bearing Wear Oil Pressure > 40 psig
8. Low Pump OR Turbine Bearing Oil Pressure < 4 psig (2/3 logic) (alarm at 5.5 psig)
MFP Trip alarm actuated if < 75 psig control oil pressure OR trip circuit is energized.

Question 4

How does the Main Feedwater Pump turbine trip?

Answer 4

MFP Trip
* HP / LP stop and control valves close
* Mini-flow valve closes
* Tripped signal to RPCB (oil pressure)
* Red light lit when tripped

Question 5

What is the capacity of a Main Feedwater Pump?

Answer 5

Each pump can supply up to approximately 60% of the total feedwater flow requirements of the plant at rated power.

Actual feedwater flow is determined by the speed of the turbine powering the pump. (Normal pump speed is 4155 to 5775 rpm with a speed limiter setting of 5,889 rpm.)

Question 6

What is the capacity of the High Pressure Feedwater Heaters?

Answer 6

High Pressure FW Heaters (5, 6, 7)
* Two train (3 heaters each)
* 75% flow per train
* 25% heater bypass line
* Heats the feedwater ~ 101°F
o Outlet temperature ~ 449˚F
* **Power is limited with one train OOS **to prevent undue loading or overstressing of turbine components.

Question 7

How do the Main Feedwater Pump Mini-Flow Valves (FV-1 / FV-2) fail on a loss of:
air
controller(120 vac NNN)
power (120 vdc NKN)

Answer 7

• Loss of air: Fail open.
• Loss of 120 Vac to controller: Fails Open (Reverse acting controller)
• Loss of 125 Vdc (NKN):
• **Fails As-Is **if the MFP is not tripped (no affect on the mini-flow operation)
• **Fails Open **if MFP is Tripped (low flow signal)

Question 8

How many speed sensors are on the MFP’s?

Answer 8

• Speed Pickup Detector Assembly (4 sensors)
  o 2 - internal governor control
  o 1 - speed reference signal to local tach and to MCR speed indicator
  o 1 - signal to the turbine supervisory instrumentation (computer input)

Question 9

What determines MFP speed?

Answer 9

• Speed determined by position of Control Valves.
  o Valve positions are controlled by the operating cylinder. Operating cylinder is controlled by the speed governor.
  o Governor controlled by DFWCS or manual speed control potentiometer in MCR.

Question 10

Describe the impacts to MFP on a loss of NNN-D15/16

Answer 10

Loss of NNN-D15
* A MFP control valves fail closed (trip without a RPCB)
Loss of NNN-D16
* B MFP control valves fail closed (trip without a RPCB)
* Loss of stop valve VPIs (both MFPs)

Question 11

Describe the impacts to MFP on loss of NKN-D41/42/43

Answer 11

Loss of NKN-D41 (125 Vdc)
* **A MFP Trip **and Reset circuit loses power (local manual trip only).
* A MFP mini-flow SOVs lose power (will not close on a MFP trip)
* MFP suction pressure drops (A HDT Pump discharge closes, HDT pump recircs open, A/B Cond Pump recirc open)

Loss of NKN-D42
* MFP suction pressure drops (C Cond Pump recirc opens)

Loss of NKN-D43
* B MFP Trip and Reset circuit loses power (local manual trip only)
* B MFP mini-flow SOVs lose power (will not close on a MFP trip)
* MFP suction pressure drops (B HDT Pump discharge closes)

Question 12

What is the capacity of the Main Feed Water Pump Mini-Flow Valves (FV-1 / FV-2)?

Answer 12

MFWP Mini-Flow Valves (FV-1 / FV-2)
* ~** 5000 gpm flow capacity**
o Mechanically limits flow to 5000-7000 gpm.
(Normally closed when > 30% power)

Question 13

What is the capacity of the Main Feed Water Pump Mini-Flow Valves (FV-1 / FV-2) respond to a MFP Trip?

Answer 13

*** Auto close on MFP trip **(< 75 psig oil pressure)
o Energizes two 125Vdc SOVs to align closing air. (Air to top, vents the bottom)
o Prevents freewheeling.

Question 14

What is the purpose of the internal pilot valve in the Low Pressure stop valves of the Main Feedwater Pump Turbine?

Answer 14

LP Stop Valves
* Hydraulically operated by the HP oil system (full open (MFP reset) or closed (MFP trip))
* Internal pilot equalizes pressure across main valve to allow it to open

Question 15

What does the Low Pressure Stop Valve Test Switch do?

Answer 15

• LP Stop Valve Test Switch (MCR or local): Strokes to a mid-position. Limit switch stops valve motion. Reopens when released.

Question 16

What does the High Pressure Stop Valve Test Switch do?

Answer 16

• HP Stop Valve Test Switch (MCR or Local)
  o Logic requires the HP control valve to be fully closed.
  o Prevents low SGWL trip if the MFP is on HP steam.
  o Local Green light LIT when HP control valve is closed (test is circuit enabled)
  o “Test” pushbutton closes the stop valve. Valve reopens when released.

Question 17

What is the interlock for the Low Pressure/High Pressure stop valves on the Main Feedwater Pump Turbines?

Answer 17

• Interlock to open: LP/HP Control Valve closed