SGWL Flashcards
What is the purpose of the Steam Generator Water Level Control system?
To regulate steam generator feedwater flow such that
- Feedwater flow matches steam flow
- Steam generator water levels are maintained within normal operating limits
Maintains indicated steam generator level above the Low Steam Generator Level trip setpoint (25.9%) and below the High Level Override setpoint (84.7%) for:
- Step load changes of +/- 10% of rated
- Ramp load rate rise of up to 5% per minute.
- Ramp load rate lowering of up to 15% per minute.
What is the steam generator water level control operational design?
Uses three elements of control:
- Steam generator level
- Feedwater flow
- Steam flow
Processed within Main Feed Reg Valve Level Indicating Controllers, LIC‑0701, LIC‑0703
SGWLC is “Level Dominant” signal is determined based on the S/G Level error (Actual level vs. Setpoint) as measured in the downcomer region
This signal is fine tuned via
- Mismatch between Main Feedwater Flow and Main Steam Flow
How does the Automatic Control within LIC-0701/0703 function with the feed pumps and Main Feedwater Regulating Valves to control level?
Signal based on SG water level in downcomer, modified by mismatch between feed flow and steam flow.
Signal Sent to:
- Feedwater Regulating Valve Controller to modulate the Feed Reg Valve (CV-0701/0703)
- Main Feed Pump Combined Speed Controller and ultimately to the individual Feed Pump Speed Controllers to change the Turbine Driver (K-7A/B) speed for its respective Main Feed Pump.
The feedwater regulating valve controller in combination with the turbine driver speed control system will function to control the level in each steam generator by modulating the feedwater flow.
Normal operating level (setpoint) is 65% at power
How does the MFP speed control HIC-0525 function within the SGWL system?
HIC-0525, when in cascade, selects the signal via LIC-0701/0703 from the steam generator requiring the higher feedwater flow which is compared to a feedback signal from turbine speed in the speed controller of each driver.
Any difference between the two signals will cause the speed controllers to produce a change in turbine speed in the appropriate direction.
How does MFP fixed speed control function with SGWL?
At low power levels (< 25% power) a single element control unit (Individual Pump Speed Controller) is used.
- The turbine driver speed control system can be divorced from the feedwater regulating system.
- Operated automatically to maintain parallel operation of each turbine driver at a manually set speed.
- Feedwater regulating valve system will then function to control steam generator level by automatically throttling the discharge of the feed pumps.
How do Main Feed Reg Valve Level Indicating Controllers, LIC‑0701, LIC‑0703 function?
Use steam generator water level in downcomer region as primary signal source.
Output signal refined by mistmatch between steam flow and feed flow.
- Outputs a signal to its respective Feed Regulating Valve positioner and to the Combined Speed Hand Indicating Controller, HIC-0525.
Indications
- Red Pointer - actual S/G level
- Blue Pointer - Level Setpoint
- Slider Scale - Output signal (0-100%)
- PV- Process Variable
- SV- Setpoint Variable
- MV- Manipulated Variable (value of output meter)
Operating Modes
- PF Key non-functional
- Only Auto and Manual modes are operational.
- Cascade is inhibited and cascade push button does not illuminate.
To transfer from manual to auto
- Green PF light flashes when actual level is within 5% of setpoint
- Match set point to process (green flashing light) and press AUTO
- Bumpless transfer to manual, manual tracks auto
- Transfer to AUTO is blocked if turbine trip signal is active (e.g., 386 AST relay has actuated)
- Transfers to MANUAL on 386 AST.
Large feedwater transients are minimized by controller design which limits how quickly the output signal is generated when controller is in Auto and the setpoint is changed
How do Main Feed Reg Bypass Valve Level Indicating Controllers, LIC‑0734, LIC-0735 function?
Identical to LIC-0701 and LIC-0703, except
- Single element control and the controller output signal is generated from the mismatch (error) between actual S/G level and setpoint.
What is the purpose of the Main Feed Reg Bypass Valves, CV-0734, CV-0735?
Main Feed Reg Bypass Valves, CV-0734, CV-0735
- Bypass valves purpose is to enable finer control of S/G level at low flow conditions vis single element of SGWL program
- Main Feed Regulating Bypass Valves are at least 50% open (70% preferred).At least 80 MWs Turbine load (90 preferred)
- DP between the Main Feed Pumps and the S/Gs should be 150 to 200 psid.
- Since Main Feed Pump speed is in manual control, ensure following parameters are closely monitored:
- Valve position indication
- S/G levels
- Controller response
Valves fail “as is” on loss of air.
What is the function of the Combined Speed Hand Indicating Controller, HIC-0525?
Combined Speed Hand Indicating Controller, HIC-0525
Modes of Operation
- Cascade
- Auctioneers the largest signal from the S/G Level Controllers, LIC-0701 or LIC-0703, and pass this signal on to the Feed Pump Individual Speed controllers
- Manual
- Provide a signal to the Feed Pump Individual Speed Controllers
- Auto
- Not functional, and only used when transferring from Manual to Cascade.
- PF Key non-functional
Indications
- BLUE - auctioneered largest % signal from LIC‑0701/03 (input to controller or “setpoint demand”)
- RED - % signal being sent to HIC‑0526/29. Should match output indicator
- PF light flashes when set point and process are matched (within 0.5%) and indicate that swap to CASCADE is permissible (push AUTO button first)
- PV- Process Variable
SV- Setpoint Variable
MV- Manipulated Variable (value of output meter
- The 0% to 100% signal is equivalent to a feed pump speed of 0 to 6000 rpm.
- HIC-0525 output ranges 54.2% to 87.5% cover MFP governor control range of 3250 rpm to 5250 rpm.
In order to use this controller to control pump speed, individual pump controller(s) (HIC-0526 and/or HIC‑0529) must be in CASCADE.
How do Main Feed Pump Speed Hand Indicating Controllers, HIC‑0526, HIC-0529 function?
Designed to control Main Feed Pump Turbine speed between 3250 to 5250 RPM. On Governor only.
Tuned to ensure pumps respond slowly to signal changes from the Combined Speed Controller, HIC‑0525.
- Prevent Operators from inducing divergent Feed Flow oscillations due to rapid changes in setpoint
If a rapid change in pump speed is called for, the Operator must place the individual pump controllers in MANUAL and use the slide bar at the bottom of the controller to change pump speed
Modes of Operation
- AUTO buttons and PF key not functional
- PF light blinking is used for Bumpless Transfer when set point (Blue pointer) and pump speed (Red pointer) are within 0.5% of each other.
- On Turbine Trip, controller goes to the ramp down feature of the controllers - Auto Light Lit.
- CASCADE
- Individual Feed Pump Speed Controllers accept the output of the Combined Speed Controller, HIC-0525, as the setpoint for Main Feed Pump Turbine speed
Indications
- Blue pointer is RPM being called for by HIC‑0525
- Red pointer is actual feed pump speed
- PV- Process Variable
- SV- Setpoint Variable
- MV- Manipulated Variable (value of output meter
What is the design function of the Main Feed Reg Valves, CV-0701, CV-0703?
Main Feed Reg Valves, CV-0701, CV-0703
- Designed to provide adequate flow to the S/Gs so that level is maintained at setpoint by the Steam Generator Water Level Control program from 15% power to 100% power.
- Valves fail “as is” on loss of air. Drift closed.
What is the function of the S/G Level Transmitters, LT-0701, LT-0703?
S/G Level Transmitters, LT-0701, LT-0703
Control Channels
- Range is 0% to 100
- Narrow range instruments are “hot calibrated” and are the indication of choice when at rated temperature and pressure conditions.
What is the function of the S/G Level Transmitters (LT-0758A/B, LT‑0757A/B)
S/G Level Transmitters (LT-0758A/B, LT‑0757A/B)
Primary use is during transients involving low S/G levels (<0% level) and when the PCS is cold
- Cold Calibrated
- Range is –140% to +150%
What is the function of Steam Flow Transmitters, FT-0702, FT-0704?
What happens if the pressure signal to the steam flow transmitters fails high or low?
Steam Flow Transmitters, FT-0702, FT-0704
- Range is 0 to 6E6 Lbm/hr steam flow
- S/G main steam flow input to the S/G Three Element Controllers
- LIC-0701 and LIC-0703
Pressure signal fails low, indicated flow will decrease to a lower value.
Pressure signal fails high, indicated flow will increase to a higher value.
Due to changes in pressure causing changes in density without a corresponding change in sensed DP.
How does CHP interact with the SGWL control program?
Containment High Pressure (CHP)
- Affects FRVs and FRV Bypasses
- Signal output of LIC‑0701/0703 is grounded. Therefore the FRV goes closed and the HIC-0525 signal is zero.
- On a Containment High Pressure, normally both channels of CHP would actuate, therefore both FRVs and FR Bypass valves go closed.
- Feed Reg Bypass Valve closure signal may be overridden by use of key switch on C-01 panel HS-0735/34. Allows use of feed system to feed a S/G in event it is needed to cool the primary.
- CHP signal override applies only to the Feed Reg Bypass valves
What is the function of the Steam Flow Transmitters, FT-0702, FT-0704?
- Range is 0 to 6E6 Lbm/hr steam flow
- Designed to provide a S/G main steam flow input to the S/G Three Element Controllers (LIC-0701 and LIC-0703)
What is the function of Feed Flow Transmitters, FT-0701, FT-0703?
How does a dp flow transmitter work?
Feed Flow Transmitters, FT-0701, FT-0703
- Range is 0 to 6E6 lbm/hr feedwater flow
- Designed to provide a S/G main feedwater flow input to the S/G Three Element Controllers (LIC-0701 and LIC-0703)
Flow rate is directly proportional to the square root of the differential pressure
How does Low S/G Pressure interact with SGWL?
Affects FRVs and FRV Bypasses
The FRV and FRV bypass close only on the S/G with the low pressure
- Basis for the S/G low-pressure closure.
- Limit mass addition to the containment structure in event of a main feed line break.
- Assumes S/Gs de-pressurized and feed is supplied by condensate pumps.
- Consequences of continuing to feed a S/G with a steam line break:
- PCS overcooling
- Possible containment over pressurization
How does High Level Overide affect SGWL?
High Level Overide
- Affects FRVs only
- Actuated by level indicating alarms LIA‑0702/ LIA‑0704 on steam generator E‑50A/B at 84.7%
- Grounds the signal from the SGWLC three element controllers (LIC-0701/0703) to the Main Feedwater Regulating Valve positioners.
- No signal, valves go closed
- Once the high level condition is clear, the signal ground is cut out and the HLO is removed.
- Only the FW Regulating Valves associated with the S/G with the high level is affected.
What is the purpose of the high level overide?
Prevent moisture carryover to the turbine which could possibly result in turbine damage.
How does a Turbine Trip affect SGWL control?
- (LIC-0701/0703) transfer from auto to manual.
- MFRVs remain in their “as is” position.
- If HIC‑0526 and HIC‑0529 are in CASCADE, their controllers automatically shift to the AUTO mode and their auto signal will ramp down to zero.
- Operator takes manual control of the Individual Feed Pump Speed controllers, and ramps down the output to minimum speed.
- Prevents Overcooling of the PCS and the resulting PCS depressurization to the SIS setpoint due to the tuning of the Individual Speed Controllers in AUTO mode (output response is too slow in AUTO).
- Operators use manual control to close MFRVs.
How do LIC-0701 and LIC-0703 react to a CHP, Low SG Pressure and High Level SG ground?
- Do NOT respond to a grounded signal as it is grounded downstream from the controller
- Controller is still monitoring S/G level and feed flow and steam flow. Its response will be based upon this fact plus the fact that the respective FRVs are closed, thus no flow to the affected S/G. Therefore, if the controller is in AUTO, its signal output will show 100% (assume no plant trip).
- The Operator must look at the Feed Regulating Valve position indication on C-01 and the PPC to determine actual valve position.
What are the power supplies for A SGWL components?
Most ‘A’ SGWLC equipment is normally powered from EY-10 and will automatically transfer to EY-30 on loss of EY-10, and will transfer back when power restored.
- All associated flow transmitters for Main Feedwater control for E-50A, ‘A’ S/G including feed flow, steam flow, steam pressure, S/G level are powered from this supply.
What are the power supplies for B SGWL components?
Most ‘B’ SGWLC equipment is normally powered from EY-20 and will automatically transfer to EY-40 on loss of EY-20 and will transfer back when power restored.
- All associated for transmitters for Main Feedwater control for E-50B, ‘B’ S/G including feed flow, steam flow, steam pressure, S/G level are powered from this supply.
