ML19094A559

Response to Request for Additional Information Systems Capabilities of Handling Degraded Voltage Conditions

ML19094A559
Person / Time
Site:	Surry
Issue date:	09/26/1977
From:	Stallings C Virginia Electric & Power Co (VEPCO)
To:	Case E, Reid R Office of Nuclear Reactor Regulation
References
Download: ML19094A559 (5)

Text

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VIRGINIA ELEOTRIO AND POWER COMPANY RxoHMOND,VXRGINIA 23261 September 26,

• 1977

• Mr. Edson G. Case, Acting Director Nuclear Reactor.Regulation Serial No. 234A/060377 PO&M/TAP:das U. S. Nuclear Regulatory Commission Washington, D. C.

20555 Attn:

Mr. Robert W. Reid, Chief Operating Reactors Branch 4

Dear Mr. Case:

Docket Nos~ 50-280 50-281 License Nos. DPR-32

-- -- -*--DPR-37* -:----

This letter is to present. the results of our analyses of your June 3,* 1977, request for further information on our system's capabilities of handling degrad-ed voltage conditions.

We have reviewed our system with your staff and believe that our present system capabilities are adequate.

Also,.we are submitting for your study a proposed addition to our surveillance requirements.

Specifically, our responses to your Staff Positions as discussed at our meeting of September 6, 1977,* follow:

1)

Position 1:

Second Level of Under-or-Over Voltage Protection With a Time Delay We require that a second level of voltage protection for the onsite power system be provided and that this second level. of voltage protection shall satisfy the following criteria:

a)

The selection of.voltage and time set points shall be.

determined from an analysis of the voltage requirements of the safety~related loads at. all onsite system distri-bution.levels.

Response

Our letter serial number 197 /081276 dated November 3, 1976,

.thoroughly.describes the voltage protection.features employed.

We will.briefly summarize our system capabilities.

The emergency buses are fed from the Reserve Station Service Transformers which each have an automatic tap changing feature.

This tap changer is activated by a. change in output voltage of +/-1.25%

for greater *than *thirty* seconds at which time the tap changer changes in *increments of

• 625%. per second for* 16 steps.

Thus, our first. level of protection protects the emergency buses, plus or minus 10%, around the normal line volt_age.

e VIRGINIA ELECTRIC AND POWER COMPANY TO Mr. Edson G. Case Page No. 2 Our undervoltage detection and actuation is by coincidence logic of 2/2 relays per bus.

The relays have LV coils which.have response characteristics as shown on the attachment.

Therefore, even though the setpoint of diesel start at 84% of nominal voltage and of isola-tion from off-site power at 79.5% of nominal voltage occurs at 12 se-conds from the time of reaching.the setpoint, other conditions of.

undervoltage will also.be detected. For exi:i.ID.ple, on complete loss of voltage the* relays will trip in 1.2 seconds.

With these two levels of protection, the emergency bus is pro-tected at all points except for the range of 80-90% undervoltage.

However, our safety grade motors were all purchased to start *at 70%

of rated voltage and thus the motors*will all start and accelerate through the range of 80-90% of nominal voltage. If the transient de-graded voltage condition does not last longer than normal starting times (10~30 seconds) the motors will suffer no harm.

Any longer period than that may b_egin to reduce their useful. life, but they still will respond as required during the postulated problem.

The vital buses are r_egulated to compensate for unusual volt_age conditions and the margin of setpoint charrge under the worst cases will.

be. minimal.

Another.level of disconnecting the en:e.rgency buses from the off-site power source occurs at 45.8% of nomin.il voltage as sensed on each of the transfer buses, the method of sensi~g is similar to that on the emergency buses.

Therefore, we consider our system to be in compliance with the intent of Staff Position 1. The attached proposed (for study only)

.Technical Specification change will place.our. Technical Specifications in compliance *.

2).

Position 2:. Interaction of.Ortsite *Power Sources.with*Load Shed.Feature

Response

Our system does not have a.feature to load shed the emergency buses once.the onsite source is supplying power.

Therefore, we are in compliance with Staff Position.2 *.

. 3)

Position 3: Onsite Power Source Testing

• Response The full operability*at full.load of the on-site power source is tested per Technical Specification requirement monthly.

Our Technical Specification includes a.requirement for simulating

e VIRGINIA ELECTRIC AND POWE!i COMPANY TO Mr. Edson G. Case Page l'j'o. 3 loss of offsite power in conjunction with a safety injection actua-tion signal at each refueling.

The high head and low head safety injection pumps are not started but the breakers are placed in test to preclude a RCS overpressure accident per a prior NRC commitment.

This serves the intent as the pumps are proved operable monthly and this test proves the starting sequencing during accident conditions and proper diesel loading.

The difference in.diesel load is minimal as we have no load sequencer, and the other heavy loads are not start-ed immediately during a SI condition (containment spray and contain-ment recirculation spray pumps) but would be required later.

Therefore, the monthly testing proves the operability under full

.load of the onsite power source; the refueling testing proves these-quencing of diesel start and load; and the refueling testing proves the starting of required loads.

We are in compliance with the intent of Staff Position 3 except for interrupting the load on the diesel.

As during emergency condi-tions our diesel is only protected by mechanical overspeed trip, we do not feel this test is appropriate nor do we believe that further trips 011 the diesel are proper during emergency conditions. Justi-fication for this load interruptiqn test is also minimal as we have no load sequencer or load shed feature on our onsite power source which could cause this postulated load interruption.

Therefore, we believe that we are in compliance with the full intent of Staff Positions 1, 2 and 3 as they apply to our facility.

Attachments cc:

Mr. James P. O'Reilly Very truly yours,

,/

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,,.-or.::..-,,...,.,..'--- I C *. M. Stallings Vice President-Power Supply and Production Operations

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ATTACHMENT Proposed (for study only) Technical Specification Change for Surry Power Station T.S. 4,6 D Emergency Bus Undervoltage Detection

1. Tests and Frequencies.

The undervoltage relays on the emergency buses shall be checked each refueling to be.within the trip values stated below:

Functional Unit Loss of Power a) 4.16 KV Emergency bus (D,E,F) Undervqltage

~Loss of Voltage) b) 4.16 KV F.mergency bus (Il, J) Uuder--.;ol tagc (Degraded Vol~age)

Trip Value (_allowable tolerance) 45.8% (~5.0, -5.0%)

12 Second delay (+/- 1.0 secon<l) 80.5% (+5.0%, -5.0%)

12 Second delay (1. 0 second)