ML18044A619
| ML18044A619 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 03/07/1980 |
| From: | Huston R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Ziemann D Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8003110652 | |
| Download: ML18044A619 (7) | |
Text
consumers Power companv.
General Offices:. 212 West Michigan Avenue, Jackson, Michigan 4g201 * (617) 788-0660 March 7, 1980 Director, Nuclear Reactor Regulation Att Mr Dennis.L Ziemann, Chief Operating Reactors Branch No 2 US Nuclear Regulatory Commission Washington, DC 20555
- DOCKET 50-255 - iicENSE DPR PALISADES PLANT*- RESPONSE TO ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEMS VOLTAGES.
Consumers Power Company was requested by NRC letter dated August 8, 1979 (adequacy of station electrical distribution systems voltages) to addr~ss the questions of Enclosure 2 of that letter.
Our response is as follows:
Item 1 Separate analyses should be performed assuming the power source to safety buses is (a) the unit auxiliary transformer; (b) the startup transformer; and (c) other available connections to the.offsite network one by one assuming the need for electric power is initiated by (1) an anticipated transient (e.g.,
unit trip) or (2) an accident, whichever presents the large~t l6ad dema~d situation.
Response to Item 1 The largest load demand situation occurs following an accident which trips the unit and initiates an SIS signal.
In this situation, all of the safety injection loads are simultaneously loaded onto the 2400 V start-up transformer No 1-2.
In this analysis, the grid voltage was depressed to.95 PU and assumed a.2 starting power factor.
The plant was assumed to be fully loaded prior to the accident with these loads remaining on during the starting of the safety motors.
The analysis shows an instantaneous per unit (PU) voltage drop of.714 (Bus lC),.596 (LC 11),.588 (MCC 1),.714 (Bus lD),.583 (LC 12) and.578 (HCC 2).
If the voltage on Bus lC or Bus JD remains below.913 PU for longer than 6.5 seconds, the second level of undervoltage protection initiates a load ~
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shed and the safety loads are sequenced onto the on-site power supply (emergency diesel generators).
Item 2 For multi-unit stations a separate analysis should be performed for each unit assuming (1) an accident in the unit being analyzed and simultaneous shutdown of all other units at that station; or (2) an anticipated transient in the unit being analyzed (e.g., unit trip) and simultaneous shut~own of all other units at that station, whichever presents the largest load demand situation.
Response to Item 2 The Palisades Plant is a single-unit station; -therefore, this_ item does not apply.
Item 3 2
All actions the electric power system is designed to automatically initiate should be assumed to occur as designed (e.g., automatic bulk or sequential loading or automatic transfers of bulk loads from one transformer to another).
Included should be consideration of starting of large non-safety loads (e.g.,
condensate pumps).
Response to Item 3 All protective circuitry is assumed to operate as designed.
The pl~nt's large nonsafety loads (condensate, primary coolant and cooling tower) are on 4160 V buses.
Analysis shows that motor starts on the 4160 V system have negligible effect on the voltages on the 2400 V safety buses.
Item 4 Manual load shedding should not be assumed.
Response to Item 4 Voltage drop calculations for the Palisades Plant do not assume manual load shedding.
Item 5 For each event analyzed, the maximum load necessitated by the event and the mode of. operation of the plant at the time of the event-should be assumed in addition to all loads caused by expected automatic actions and manual actions permitted by administrative procedures.
Response to Item 5 This item assumes the largest load situation which.is covered in Item I of this response.
Item 6 3
The voltage at the terminals of each safety load should be calculated based on the above listed considerations and assumptions and based on the assumption that the grid voltage is at the "minimum expected value."
The "minimum expected value" should be select.ed based on the least of the following:
- a.
The minimum steady-state voltage experienced at the co~ection to the offsite circuit.
I
- b.
The minimum voltage expected at the connection to the offsite circuit due to contingency plans which may result in reduced voltage from this grid.
- c.
The minimum predicted grid voltage from grid stability analysis (e.g.,
load flow studies).
In the repo.rt to NRC on this matter the licensee should state planned actions, including any proposed "Limiting Conditions for.Operation" for Technical Specifications, in response to experiencing voltage at the connection to the offsite circuit which is less than the "minimum expected value." A copy of the plant procedure in this regard should be provided.
Response to Item 6 As stated in the response to Item I above, our analysis is performed assuming that the grid voltage is.95 PU.
This is the "minimum expected value" of the predicted grid voltage.
Consumers Power Company does not intend to include any "Limiting Conditions for Operation" for the Technical Specifications in response to experiencing voltage at the connection to the off-site circuit which is less than the "minimum expected value." If the grid voltage becomes less than.95 for a sustained time period, the recently installed second level of undervoltage protection would cause load shedding that would take the plant off line ~r prevent it from starting up.
This second level of undervoltage protection provides a built-in "Limiting Condition for Operation."
Item 7 The voltage analysis should include documentation for each condition analyzed, of the voltage at the input and output of each transformer and at each intermediate bus between the connection to the offsite circuit and the terminals of each safety load.
Response to Item 7 As stated in the response to Item 1, the largest load demand situation occurs when all of the safety injection loads are simultaneously loaded onto the 4
2400 V start-up transformer No 1-2 with the grid voltage at.95 PU.
The P1161 program provides values for voltage on the input and output for each trans-former and* intermediate bus.
Item 8 The analysis should document the voltage setpoint and any inherent or adjust-able (with nominal setting) time delay for relays which (1) initiate or execute automatic transfer of loads from one source to another; (2) initiate or execute automatic load shedding; or (3) initiate or execute automatic lqad sequencing.
Response to Item 8 The attached Drawing SK-E-100 (Attachment 1) was generated as part of the Undervoltage Protection Modification.
This drawing shows the voltage set points and time delay relays involved in undervoltage protection, load transfers, load shedding and load sequencing.
Item 9 The calculated voltages at the terminals of e~ch safety load should be compared with the required voltage range for normal operation and starting of that load.
Any identified inadequacies of calculated voltage require immediate remedial action and notification of NRC.
Response to Item 9 The second level of undervoltage protection prevents the safety load terminal voltage from dropping below the required range for normal operation and starting of that load.
Inadequate voltages have been eliminated by the second level of undervoltage protection.
Item 10 For each case evaluated the calculated voltages on each safety bus should be compared with the voltage-time settings for the undervoltage relays on these safety buses.
Any identified inadequacies in undervoltage relay settings require immediate remedial action and notification of NRC.
Response to Item 10 The voltage-time settings for the second level of undervoltage relays were initially chosen as a result of our voltage drop calculations.
The load configuration has not changed since these calcul~tions were made so there is no need to reevaluate the settings.
5 Item 11 To provide assurance that actions taken to assure adequate voltage levels for safety loads do not result in excessive voltage, assuming the maximum expected value of voltage at the connection to the offsite circuit, a determination should be made of the maximum voltage expected at the terminals of each safety load and its starting circuit. If this voltage exceeds the maximum voltage rating of any item of safety equipment immediate remedial action is required and NRC shall be notified.
Response to Item 11 This determination was made as a result of the NRC's letter.dated June 3, 1977.
Consumers Power Company reported this determination in our letter dated October 2, 1978.
Item 12 Voltage-time settings for undervoltage relays shall be selected so as to avoid spurious separation of safety buses from offsite power during plant startup, normal operation and shutdown due to startup and/or operation of electric*
loads.
Response to Item 12 The values for voltage-time settings for undervoltage relays were addressed in our letter to the staff dated October 2, 1978.
Setting selection involved consideration of avoiding spurious separations and protection of safety loads from sustained undervoltage.
Item 13 Analysis documentation should include a statement of the assumptions for each case analyzed.
Response to Item 13 All major assumptions are itemized in the response to Item 1.
The staff has al.so requested more information on how Consumers Power Company intends to verify our analysis by test.
The following is a description of the method intended to be used in performing this verification:
The Palisades Plant routinely performs surveillance Test R0-8 which assures that the plant can start the safety injection loads from.off-site power and then repeat the loading sequence using on-site power.
.The closest simulation of the worst case voltage drop conditions is to monitor the voltage drop experienced from simultaneously starting all of the safety injection loads off of the 2400 V start-up transformer No 1-2.
6 The test will involve taking strategic voltage, current and power readings just prior to the motor startings.
This will model the exact plant loadings at the time of the test.
Oscillographs will record the voltage drop from the motor starts.
A case which models the motor starts is then prepared.
The verification will be made by comparing the voltage drop from the computer case with the actual oscillograph readings.
This method of verification testing was discussed with members of the staff on August 21, 1979 and was verbally approved.
The test results will be submitted for staff review upon completion of the test and the computer case.
Senior Licensing Engineer CC JGKeppler, USNRC
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ATTACHMENT 1 2
LOADS
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BECHTEL AU ARBOR. lllCHIGU PALISADES PLANT CONSUMERS POWER COMPANY GWO 8538 U
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D C TIO S LOGIC DIAGRAM 2.'IKV SAF(TY BUSES I*("' 1*0 UNDl:RVOLTAG[ PROTECTION A DllAWHl8...
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