GO2-82-807, Final Deficiency Rept Re High Resistance Cable Grounding of 4.16 Kv Diesel Generators.Initially Reported on 820506. Manufacturers Advised That Equipment Can Operate for Indefinite Period w/line-to-ground Fault W/O Damage

Final Deficiency Rept Re High Resistance Cable Grounding of 4.16 Kv Diesel Generators.Initially Reported on 820506. Manufacturers Advised That Equipment Can Operate for Indefinite Period w/line-to-ground Fault W/O Damage

ML20063P242
Person / Time
Site:	Columbia
Issue date:	09/28/1982
From:	Matlock R WASHINGTON PUBLIC POWER SUPPLY SYSTEM
To:	Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V)
References
10CFR-050.55E, 10CFR-50.55E, GO2-82-807, NUDOCS 8210130217
Download: ML20063P242 (3)

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Washington Public Power Supply System P.O. Box 968 3000GeorgeWashingtonWay Richland, Washington 993527(509)372-5000 Docket No. 50-397 'N DP September 28, 1982 G02-82-807 Mr. R. H. Engelken U.S. Nuclear Regulatory Commission Region V 1450 Maria Lane, Suite 210 Walnut Creek, California 94596

Subject:

NUCLEAR PROJECT NO. 2 10CFR50.55(e) POTENTIALLY REPORTABLE CONDITION #189, HIGH RESISTANCE CABLE GROUNDING 0F THE 4.16KV DIESEL GENERATORS

Reference:

Telecon L.C. Floyd to T. D'Angelo, dated May 6, 1982, same subject.

In accordance with the provisions of 10CFR50.55(e), your office was informed, by telephone, of the above subject potentially reportable condition on May 6, 1982. Attachment A provides the Project's final report on Condition #189.

If there are any questions concerning this matter, please contact Roger Johnson, (509) 377-2501, extension 2712.

o Program Director, WNP-2 LCF/kd

Attachment:

Final Report cc: W.S. Chin, BPA - Site A. Forrest, Burns and Roe - HAP 0 N.D. Lewis, NRC J. Plunkett, NUS Corp.

R.E. Snaith, Burns and Roe - NY V. Stello, NRC A. Toth, WNP-2 NRC Resident Inspector Site Files 9178 8210130217 820928 99 PDR ADOCK 05000397 O PDR CO

ATTACl#4ENT A WASHINGTON PUBLIC POWER SUPPLY SYSTEM NUCLEAR PROJECT NO. 2 DOCKET NO. 50-397 LICENSE NO. CPPR-93 HIGH RESISTANCE CABLE GROUNDING OF THE 4.16 KV DIESEL GENERATORS 100FR50.55(e) POTENTIALLY REPORTABLE CONDITION #189 FINAL REPORT Description of Deficiency WNP-2 uses a high resistance grounding system for the 4.16 KV and 480 V essential power systems (Class lE). The advantage of this system is to allow operation of the system with a single line-to-ground fault.

It is not mandatory that this type of system be utilized on nuclear power plants, but plant and equipment availability is improved. The operator is advised via annunciation in the main control room that a ground fault exists. However, the annunciators are not Class lE. On the 4.16 KV switchgear, individual feeders are alarmed in the control room. For 480 V switchgear, the feeder for the switchgear is alarmed and local indication at the switchgear indicates the faulted feeder from the switchgear.

The indicated deficiency is that the system cables and equipment cannot operate for indefinite periods of time with a single line-to-ground fault.

Analysis of the Safety Implications All equipment manufacturers (switchgear, motors, diesel generator, etc.)

have been contacted and they have advised us that their equipment can operate for an indefinite period of time with a line-to-ground fault without damage.

For the 100% insulation level of 5 KV cable, the maximum rated line-to-ground voltage is SKV/d=2890V. At the 133% insulation level which is the rating of the Okonite cable on WNP-2, the maximum rated line-to--

ground voltage is 2890V x 1.33 = 3844V. The impressed line-to ground voltage on the line-to-ground fault will be 4160V, This is approximate-ly 8% above the cable rating for the 133% insulation level. However, the 133% insulation level allows operating on a line-to-ground fault for one (1) hour. See IPCEA Publication No. S-68-516.

After one (1) hour, some degradation of cable life may occur, but this amount of degradation is not definable.

On the 480V system, 1000V cable is utilized. This insulation is accept-able for line-to-ground faults for an indefinite period of time.

Final Report Page Two Corrective Action Taken The 5 KV cable with 133% insulation level is acceptable. This cable has been used on high resistance grounded systems in numerable instal-lations in nuclear power plants without detrimental consequences. Addi-tionally, line-to-ground faults are unusual occurences. Since the degra-dation of cable life is unknown after one (1) hour, the following admin-istrative controls will be utilized:

a. The technical specifications will include directions to the oper-ators that ground faults should be cleared manually within one (1) hour if plant availability and reactor safety is not jeopardized.

b. If a line-to-ground fault cannot be isolated within one (1) hour, the 5 KV cables connected to the 4.16 KV essential bus will be tested after the bus is de-energized. Tests will be in accordance with cable manufacturer's recommendations to show that the cable is capable of performing its intended 40 year life.

c. If the cable does not pass the tests in (b) above, the cable will be replaced.

This item has been determined to be not reportable under 10CFR50.55(e).

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