ML19347D488
| ML19347D488 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 03/23/1981 |
| From: | Hoffman D CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8103260156 | |
| Download: ML19347D488 (8) | |
Text
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Company o.a.rw ovne.s: 212 West Michigan Av.nu., J.ckson, MI 49201 * (517) 788 0550 March 23, 1981
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I kYh'7 Director, Nuclear Reactor Regulation
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Att Mr Dennis M Crutchfield, Chief
,,4 Sp, [2 Operating Reactors Branch No 5 g4 US Nuclear Regula.ory Commission 9
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v Washington, DC 20555 g
DOCKET 50-155 - LICENSE DPR %g BIG ROCK POINT PLANT - GENERIC
/
4 ISSUE - ADEQUACY OF STATION Q
ELECTRIC DISTRIBUTION VOLTAGES NRC letter dated January 27, 1981 requested Consumers Power Company to provide additional information relating to the generic issue of the adequacy of station electric distribution voltages.
Attachment I to this letter provides our responses to those information requests in the same numerical scheme.
David P Hoffman (Signed)
David P Hoffman Nuclear Licensing Administrator CC Director, Region III, USNRC NRC Resident Inspector-Big Rock Point oc03s'l-0262a-43
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1 A'ITACHMENT I Responses to Request for Additional Information on Adequacy of Station Electric Distribution System Voltages References NRC generic letter to all Power Reactor Licensees, " Adequacy of Station a.
Electric Distribution Systems Voltages," dated August 8, 1979.
b.
CP Co letter, David P Hoffman, to Director, Nuclear Reactor Regulation, USNRC, " Response to Generic Issues--Adequacy of Station Electric Distribution System Voltages," August 29, 1980.
c.
CP Co letter, David P Hoffman, to Director, Nuclear Reactor Regulation, USNRC, " Response to Generic Issue--Degraded Grid Voltage," August 21,
- 1980, d.
CP Co letter, William S Skibitsky, to Director, Nuclear Reactor Regu-lation, USNRC, "On-Site Emergency Power Sources," June 14, 1978.
Item 1 For each previously analyzed case (References b, c & d) and for the analyses required by the following questions, please supply the calculated voltages and the voltage ratings for all low voltage AC (less than 480V) Class 1E equipment (including the alternate source for any motor-generators or inverters). Do these systems supply any instruments or control circuits as required by GDC 137 If so, is all the equipment capable of sustaining the analyzed voltages without blowing fuses, overheating, etc, and without affecting the equipment's ability to perform the required function?
Response to Item 1 Previously analyzed and submitted cases were for equipment rated nominal 480 V and above. These analyses do not include the effect of low voltages on Class 1E equipment which is rated less than 480 V nominal. General Design Criteria 13 requires instrumentation to monitor variables and systems over their anticipated ranges for normal operation, for anticipated operational occurrences and for accident conditions to assure adequate safety. The Big Rock Point Plant i.as Class 1E equipment which is rated 120 V ac and is used to comply with the requirements of GDC 13.
GDC 13 is purposely vague about specific instruments which are required due to the uniqueness of each plant.
It is, therefore, necessary to develop a list of instruments and other 120 V ac equipment which is required to perform a safety function. Work activities recently completed for the Systematic Evaluation Program (SEP) provide the input for this list. The SEP list includes equipment which is 480 V and above, de and some mechanical equipment.
The SEP list was, therefore, reduced to include only 120 V ac equipment. The list was further reduced by evaluating the failure mode of the equipment.
By nu0381-0262a-43
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this process, the original list of safety equipment was reduced to include only power supplies for instrument loops.
These instrument power supplies are fed from 120 V Instrument and Control Panels 1Y and 3Y.
These are, in turn, supplied from either 480 V Hotor Control Center (MCC) 1A or MCC 2B through their respective instrument transformers. As previously submitted, the second level of undervoltage protection was installed to protect the 480 V MCCs from sustained voltages below 85%.
Voltage drop calculations were performed between the 480 V MCCs and each instrument power supply. The worst case shows a voltage drop of only 2%.
The smallest voltage drop was only 0.3%.
These voltage drops were added to the assumed 85% voltage at the MCC and the resultant was compared with the ratings of the instrument power supplies. The worst case shows a voltage only 4.4%
below the guaranteed rating of the power supply. The best case shows a voltage only.17% below the guaranteed rating of the power supply.
Each of the power supplies and their corresponding instrument loops were evaluated to determine the effect of these voltages on the ability of the equipment to perform their safety functions.
Informal tests in the past have shown that an instrument loop will continue to provide a current signal as long as the transmitter oscillator is functional. The transmitters remained functional even down to input voltages of 30%. The percent error in the current signal is dependent on the age of the equipment and the degree of undervoltage and is not necessarily directly proportional to the input voltage.
In each case, a reduced voltage would result in a downscale reading on the indicator. For the instruments analyzed above, the downscale reading would result in a safety function occurring sooner or an operator taking a more conservative reading.
Finally, the instrument loop is probably monitoring a transient condition (flow indication) and the undervoltage condition is timed out at 10 seconds which results in a transfer to a different power source (diesel generator).
It is inconceivable that an error of 4.4% or less while monitoring a transient condition for 10 seconds or less will cause the maloperation or failure of any equipment in the instrument loop or cause significant misinterpretation by the operators. These reduced voltages, over the 10-second time range, will not result in the overheating of the power supply, blown fuses or other damage to the equipment.
The 120 V ac Instrument and Control Panels 1Y and 3Y are not supplied by M-G sets or inverters.
(Inverters are used to convert de to ac.
The dc is sup-plied from batteries and is not affected by short undervoltage conditions on the station ac distribution system.)
nu0381-0262a-43
3 Item 2 Are the analyzed cases for MCC 2A feeding Class 1E MCC 2B worse than MCC 1A feeding MCC 2B7 If not, provide the required analyses for the alternate (MCC 1A) feed.
Response to Item 2 The previously analyzed and submitted cases assumed that MCC 2B was being fed from MCC 2A.
Additional cases have since been prepared with MCC 2B being fed from MCC 1A.
The alternate MCC 1A feed will result in slightly higher voltage drops than the MCC 2A feed due to the additional 16 feet of cable from MCC 1A to MCC 2B and the additional 6 feet of cable from Load Center (LC) I to MCC 1A.
The loading on LC 2 will also result in higher voltage drops. The motor starting cases reflecting these additional voltage drops were reanalyzed and the results are summarized in Table A.
(NOTE:
Previously submitted results for the 46 kV supp.'? assumed that both the reactor fcad pumps and the circulating water pumps were being supplied from this source. The plant does not operate the reactor feed pumps while on thu 46 kV line, so these loads were removed from the analyses.)
Item 3 Provide, in percent of maximum bus loading, the loading of the buses as measured in your test verification (Reference b, Attachment II). What are the test measurement accuracies (including instrumentation and potential trans-former accuracies)?
Response to Item 3 The following summarizes the actual running bus loads and total connected bus loads based on the ampere and watt feeder readings taken during the verifi-L cation test.
SUMMARY
OF BUS LOADS Total Connected Actual / Total Bus Actual Running Bus Load (kVA)
Load (kVA)
Connected (%)
2400 V 2988 3275 91.24 LC 1 328 363 90.36 LC 2 320 363 88.15 MCC 2A 87 419 20.76 MCC 2B 9
144 6.25 All of the instruments used for the test were calibrated to i.5% accuracy.
Portable instrument transformers had an accuracy of 1 2% and permanently in-stalled instrument transformers had an accuracy of i 1.2%.
nu0381-0262a-43
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Item 4 Are the voltages supplied in your response to Item 1 (Reference c) derived from the same computer simulation (P1161) that your testing (Reference b) verified? If they are not, provide a steady state voltage analysis that has been verified by a test.
In either case descrioe the loads for the analyzed conditions.
Response to Item 4 The voltages supplied in our response to Item 1 (Reference c) were derived from the same P1161 computer program that was verified by the test.
The P1161 is the only program used by Consumers Power Company for these studies.
Our response to Item 1 (Reference c) included voltages for auxiliary systems when the supply comes from the (1) station generator, (2) 138 kV off-site system, and (3) backup 46 kV system. These analyses were performed assuming that all major 2400 V and 480 V equip =ent were operating. Actual load readings and a study of the one-line diagra=s were used to determine which minor MCC loads were on.
The total of these loads is used in the program.
The computer doesn't differentiate between individual loads that are on for each MCC; it just uses the total kVA.
As noted in the response to Item 2 above, our assumptions regarding the load-ing while on the 46 kV supply were overly conservative, so the loads repre-sented by the reactor feed pumps and circulating water pumps were removed from the base case for the 46 kV supply. The reanalyzed results are presented in Table A.
Item 5 The continuous operating voltage range for the Big Rock Point safeguards equipment is supplied by Reference d.
What are the transient operating voltage ratings (ie, rated starting and stall voltages) for this equipment?
What are the voltage ratings for your Class IE motor contactors and starters?
Response to Item 5 The Big Rock Point "lant has two different models of battery chargers (Exide and Solid-State controls). Each has a guaranteed output if the input voltage is 10% nominal. The battery chargers do not have stall and start ratings.
The manufacturers each state that an input voltage which is less than the rating of the charger would result in reduced output voltage and current. The magnitude of the reduction is dependent on the magnitude of the input voltage and the amount of load on the charger. A voltage of 85% for 10 seconds or less would not affect the batteries which, in turn, are available to provide the power for any safety functions that are required for the short duration of the undervoltage.
The safety equipment on MCC 2B includes a 100 hp fire pump and several motor-operated valves (2 hp or less). The stall and start ratings for transient nu0381-0262a-43
5 conditions are a function of voltage and can best be defined by observing the motor / pump speed torque characteristic curves. These curves are not typically prepared for every size motor by the manufacturer. This is the case for these small motors on MCC 2B.
However, the motors are generally built so as to be able to start with only 80% full voltage. According to our analysis, the safety loads would be able to start, accelerate to full speed and continue operation as required.
The contactors and starters on the Class 1E motor control centers have a rated lower limit pickup of 85% (102 V).
The lower limit for dropout is 50% (60 V).
These are values supplied by the manufacturers.
Item 6 Your response to guideline 1 (Reference b, Attachment I) provides two analyses, one for starting a reactor feed pump with the 138 kV source, the other for starting a fire pump with the 46 kV source.
Is each the worse case for that source?
If not, supply the worst case analysis for the source.
i Identify the duration of these transient conditions.
i Response to Item 6 Starting a 1500 hp reactor feed pump from the 138 kV supply is the worst case for that source.
Starting the 100 hp fire pump and the emergency motor-operated valves on MCC 2B is the worst case for that bus but is not the worst case for the off-site 46 kV supply. Transfer to the off-site 46 kV supply due to low station power voltages may require the simultaneous starting of two 440 V, 200 hp condensate pumps. This results in the worst case motor starting conditions for the 46 kV off-site supply. With the 46 kV supply at.95 Pu, the prestart voltage on LC 1 is.9454 Pu and on LC 2 is.9540 Pu.
The instantaneous voltage for starting the condensate pumps on LC 1 is.7932 Pu and on LC 2 is
.8028 Pu.
J The moter and pump speed torque curves and moments of inertia are required to perform transient analyses. These curves are not available to Consumers Power Company at this time. The motor and pump manufacturers have been contacted and the information is being collected for transmittal to us.
In the absence of this information, we were able to locate two recordings of strip chart data that were taken on two reactor feed pump star:s.
Both recordings show the pump starting and accelerating to full speed in approximately five seconds or l
less. We are confident that our analysis of the speed torque curves and inertia data will substantiate the time delay setting of 10 seconds on the second level of undervoltage protection scheme.
l l
For the start of the condensate pumps, a transient analysis is not required to substantiate the time delay setting of 10 seconds. The analysis for the con-densate pump starts shows taat the 2400 V bus voltage does not drop below the dropout voltage for the second level undervoltage relay and, therefore, the 10-second timer is not started, nu0381-0262a-43 L
l t
6 Y
Item 7 It is not clear from Figure 1 (Reference b) whether transformer No 77 is a possible source of power to the 2400 V switchgear bus or a load on that bus.
Describe the connections of this transformer at the service building.
If this is a possible power source, provide the analyses required by reference (a) and the above questions.
If this is not a source, are the effects of this connection reflected in your analyses for the 46 kV source?
Response to Item 7 Figure I was provided for the identification of the buses described in the load flow cases and was not intended to provide the details associated with the formal one-line diagrams which are available for the plant. The No 77 transformer was purposely not included in the past analyses for the 46 kV supply, since the 50 kVA transformer and its associated loads would have an insignificant effect on the studies. This load has now been added to the base data and was included in the cases that were prepared for this submittal. All future studies will also include this load.
nu0381-0262a-43
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ATTACHMENT I TABLE A 4
i Fire Pump Start-Up Summary of Bus Voltages 2400 V Bus LC 1 LC 2 Bus IA Bus 2B Case (2.4 kV)
(480 V)
(480 V)
(480 V)
(480 V)
Generator @ 1.0 Pu
.9941
.9459
.9516
.9449
.9448 Prestart Generator @ 1.0 Pu
.9863
.8622
.9434
.8557
.8494 Start-Up Generator @.95 Pu
.9411
.8894
.8956
.8883
.8882 Prestart Generator @.95 Pu
.9336
.8098
.8877
.8035
.7976 Start-Up 46 kV Swing Bus @.972
.9981
.9501
.9558
.9491
.9490 Pu, Prestart i
46 kV Swing Bus @.972
.9832
.8591
.9401
.8526
.8464 Pu, Start-Up 46 kV Swing Bus @.95
.9743
.9248
.9307
.9238
.9237 Pu, Prestart 46 kV Swing Bus @.95
.9597
.8358
.9154
.8294
.8233-Pu, Start-Up nu0381-0262b-43
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