ML19310A585
| ML19310A585 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 06/17/1980 |
| From: | Dunn C DUQUESNE LIGHT CO. |
| To: | Varga S Office of Nuclear Reactor Regulation |
| References | |
| TAC-13110, NUDOCS 8006200310 | |
| Download: ML19310A585 (7) | |
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(4:2)45s4000 435 Sixth Avese Is"$"""
June 17, 1980 Director of Nuclear Reactor Regulation United States Nuclear Regulatory Commission Attn:
Mr. Steven A. Varga, Chief Operating Reactors Branch No. 1 Division of Licensing Washington, DC 20555
Reference:
Beaver Valley Power Station, Unit No. 1 Docket No. 50-334 Adequacy of Station Electric Distribution System Voltages Gentlemen:
NRC letter dated May 1, 1980, submitted five questions related to our February 22, 1980, response to questions originally asked by the NRC during July and August 1979. Attached hereto are anst:ers to these five questions. We continue to conclude that the steps which we indicated in our February 22, 1980, response (the addition of capacitors on the 1A and 1D 4160 volt buses and the interim tap changing procedure applicable to the system station service transformers) are adequate.
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We have noted in the attachment to this letter in response to Question 2 that marginal voltages.have been calculated to exist on the vital buses if these buses are being supplied from their alternate source (480/120 inverter bypass transformers) during the conditions assumed in the Case 1 loading condition (i.e.:
low system voltage combined with CIB with reactor coolant pump running).
Even though we have decided to replace the inverter bypass transformers with regulating type transformers, we would like to point out that the configuration assumed for the Case 1
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loading is unrealistic.
Since during Case 1 loadings conditions, the 1N 480 volt bus voltage will drop to 84.5 percent of rated voltage, this will cause automatic separation of the associated 1AE 4160 V bus from its off-site source through the operation of the 480 volt undervoltage relays and will automatically transfer load onto the diesel.
This transfer of power e
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Be vsr Vcilcy Powar Statien, Unit N2. 1 Docket No. 50-334 Adequacy of Station Electric Distribution System Voltages Page 2 source will eliminate any low voltage' condition exisiting on the vital buses.
We conclude, therefore, that the low voltage condition will be maintained only during the operation time of the undervoltage relay and will have no effect on the safety of the plant.
Based upon this analysis, we conclude that the plant can be operated safely during the interim period until permanent modifications are accomplished.
Should you have further questions, please do not hesi. tate to contact my office.
Very truly yours, C. N. Dunn Vice President, Operations
- cc:
Mr. D. A. Beckman, Resident Inspector U.S. Nuclear Regulatory Commission Beaver Valley Power Station Shippingport, Pennsylvania 15077 U.S. Nuclear Regulatory Commission c/o Document Management Branch Washington, D.C.
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e 6/10/80 Reply to NRC Letter Dated 5/1/80 l
QUESTION #1 Testing has not been done to verify the results of the studies as of this date.
However, tests are being scheduled based on the following:
We will determine the station normal and emergency equipment that can be run safely (simultaneously) with the main unit off.
This load will be applied
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with the source being taken from the 138kV grid.
Included in the test will be the start of the largest 4160V motor (6000 HP) and the start of the largest motor on the 480V energency bus (300 HP).
Voltages on the various class 1E busses will be recorded before, during and after the start of the largest motors.
The grid voltage at the time of the test will be accepted.
The test-will involve only one of the two emergency bus power systems since 'they' are similar and should give the same results.
A new computer voltage study will be made.
This e tudy will duplicate, as closely as possible, the 138kV grid voltage and the loading of the actual test.
The results of the test and the study will be compared.
If these results are within reasonable a.greement, we will conclude that the study values simu-lat ing minimum syst em (grid) voltage and accident loading previously sent to l
you are verified.
We will provide a test report substantiating the results of this analysis.
We propose this approach to the verification of our studies because it is not feasible in a test to duplicate the minimum system voltage / accident con-ditions.
First, it would require forcing the 138kV grid to a minimum voltage condition, which is undesirable from a system operating standpoint.
- Second, various station service loads cannot be run dry without je,opardizing the equip-ment.
In our judgement, the approach we have outlined above will verify the accuracy of.the computer study.
QUESTION #2 Voltages on Class 1E Equipment Rated Less Than 480V for Cases Analyzed Case 3 Loading Condition Following are the calculated voltages on the 120/208V busses for the case -
3 loading condicion,considering also the start of a reactor coolant pump:
120/208V Heat Tracing Transformer, Sec. Voltage (TRF-BR-05) e s
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o 480/208 Tap 468/208 Tap
- 480/208 Tap 468/208 Tap
- Without Cap.
Without Cap. With Cap.
With Cap.
1 Before Start RCP 182.8V (87.9%)
188V (90.4%)
194.7V (93.6%)
200V (96.1%)
During Start RCP 142V (68.2%)
147V (70.7%)
152.5V (73.3%)
157.7V (75.8%)
Af ter Start RCP 176.7V (85%)
182V (87.5%)
189 (90.8%)
194V (93.3%)
- See discussion below.
The above transformer and other similar transformers are supplied from the 480V bus IN1.
Case 1 Loading Condition Following are the calculated voltages on 120V busses for the case 1 loading condition:
PNL-AC-El I
480/120V Tap 468/120V Tap *-
400/120V Tap 468/120V Tap
- Without Capacitors Without Capacitors With Capacitors With Capacitors 100.6V (83.8%)
103.6V (86.3%)
107.7V (89.7%)
110.6V (92.2%)
- See discussion below.
- PNL-VITBUS-1 (Thru TRF-1015)
Without Capacitors With Capacitors 100.7V (83.9%)
107.8V (89.8%)
The reactor coolant pump is not started for this case, however, the study considers the pump running.
Discussion
- d' We recognize the marginal voltages obtained and are taking steps to improve them.
The heat tracing transformers and the transformers supplying PNL-AC-El and similar busses are provided with taps..The present tap settings are 480V tap.
Taps will be changed to increase the voltage 2.5% (468V tap).
This will not cause overvoltage for light load condition;.
The transformers, such as TRF-101 above, only supply PNL-VITBUS-1 through -4 when the uninterruptible power supplies (UPS) are down for mainte-nance.
These, however, are scheduled to be replaced with regulating transfor-They will maintain the 120V vital busses within + 10%.
It shoold be mers.
noted that the vital busses are normally supplied by the UPS.
For the con-dition of low 480V system input to the UPS., the output is maintained at proper voltage levels.
We have not experienced any' equipment failures as a result of low voltages on the 120V vital busses.
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QUESTION #3 We have provided two physically independent circuits from the offsite grid in accordance with CDC17.
Our analysis indicates there are only two conditions that could cause simultaneous loss of both circuits:
1.
A simultaneous fault on both circuits.
However, the two circuits are on separate towers. We do not consider this a credible occurrence.
There are no common overcurrent devices associated with the two circuits.
The electrical protection for each is separate.
2.
Loss of the high voltage system due to a major disturbance.
With our strong interconnections with neighboring utilities and the stability of the high voltage system, we do not consider this a credible event.
For further discusion on this subject, please refer to the FSAR Section 8.3.
For each of the two cas,es above, should they occur, redundant emergency diesel generators in the station would be started automatically ^.
We, therefore, consider our design to be in compliance with GDC17.
QUESTION #4 (A) Comparison of Voltages With NRC Guidelines 3 and 9 of Ref. (b)
. The voltages on the emergency busses we obtained in our studies for the condition of starting the reactor coolant pump motor (RCP) are acceptable on the following basis:
1.
They are transient and are to be expected in the practical design of
, a system.
2.
They are inftequent 9,,7 3.
They are of short duration.
4.
They are the result of an infrequent minimum grid voltage condition.
5.
Since the starting of the RCP is manually controlled by the operator, we would not expect'that, simultaneous with starting an emergency bus load, the operator would start the RCP.
6.
We do not expect the loss of any emergency load due to the starting of the RCP.
(B) Terminal Voltages on Class IE 480V and 120V Circuits During Starting of Largest 480V Class lE Motor e
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- , 1 Following are _ the calculated bus voltages associated with starting of the largest 460V motor (300HP RS-P-1A) with all other 460V emergency loads on except the 300HP mctor:
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Voltage P.U.
on 120V Vital Bus P.U. on Bus IN (460V) 460V Base (18.8 KVA Load) 120V Base Prior to Start 443V
.963 llo.lV'
.917 During Start 368V
.800 91.lv
.759 Af ter Start 432V
.939 107.8V
.898 The above values were calculated on the basis of minimum grid voltage, 6 MVAR of capacitors. on each normal 4160V bus and the loads associated with Containment Isolation phase B without loss of offsite power.
(Case l' loading condition)
The calculated vital bus voltages are on the basis of these busses being supplied from inverter bypass transformers.
This is not the normal feed. The vital bussss are normally supplied from Uninterruptible Power Supplies (UPS);
When on this normal supply, the voltage dip will not occur.
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(CORPORATE SEAL)
Attest:
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T. Welfer, fr'.
Secretary COMMONWEALTH OF PENNSYLVANIA)
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COUNTY OF ALLEGHENY On this
/d day of
_e, 1980, before me, HENRY G. ST0ECKER a Notar % blic in and for said Commonwealth and County, personally appeared C. N. Dunn, who being duly sworn, deposed, and said that (1) he is Vice President of Duquesne Light, (2) he is duly authorized to execute and file the foregoing Submittal on behalf of said Company, and (3) the statemente set forth in the Submittal are true and correct to the best of his knowledge, information and belief.
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HENRY G. ST0ECKER, Neary Pubfc Pmburgh, A!!egheny County, Pa.
My Commission Expres February 20,1982
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