ML20090L747

Responds to Re Equipment Performance Under Degraded Grid Voltage Conditions

ML20090L747
Person / Time
Site:	Monticello
Issue date:	09/17/1976
From:	Mayer L NORTHERN STATES POWER CO.
To:	Ziemann D Office of Nuclear Reactor Regulation
References
NUDOCS 9102120606
Download: ML20090L747 (7)

Text

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v NORTHERN STATES POWER COMPA p

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September 17, 1976 hgda{0ly Docket Fidi ALic Mr. D. L. Ziemann, Chief

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Operating Reactors Branch #2 Division of Operating Reactors

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9 U. S. Nuclear Regulatory Commission A

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Dear Mr. Ziemann'

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FONTICELLO NJCLEAR GENERATING PIRif Docket No. 50-263 License No. DPR-22 Response to 8/13/76 NRC Letter on Questions Concerning Equipment Performance Under Degraded Grid Voltage Conditions This letter is in response to the request for infomation included in your August 13, 1976, 1ctter concerning equipment performance under degraded grid voltage conditions. The responses below are numbered to correspond with the questions included in enclosure 2 of the above referenced letter.

1.a.

Plant procedures require transfer of auxiliary power to an off site power source just prior to removing the generator from service. The percentage of plant operatin;; time in which power is supplied by an off site source is therefore essentially the same as the percent-age of time that the generator is off line while the reaci.or is critical. On a cumulative basis this has been 3.45%.

1.b.

The normal operating range of the 345 Kv Substation Bus voltage at Monticello is between 354 Ky and 338 Kv.

The normal operating range of the 115 Kv Substation Bus voltage at Monticello is between 125 Ky and 118 Ky.

During operation with 1R transfomer supplying station auxiliary loads the voltages at the safety related buses for the above range of 115 Kv Substation voltage will be as follows:

9574 9102120606 760917 PDR ADOCK 05000263 P

PDR

m 125 KV 118 KV 4.16 Kv Bus 15 4400 4155 4.16 Kv Dus 16 4350 4100 480v L.C.103 483 458 480v L.C. 104 477 449 1AR Transfomer is another source for the safety related 'Uuses. The voltages at the safety related buses with 1AR under no load conditions and the range of 345 Kv Substation voltages specified above will be as follows:

354 KV 338 KV 4.16 Ky Bus 15 4210 3995 4.16 Kv Bus 16 4210 3995 480v L.C. 103 486 460 480v L.C.104 486 460 If 1AR transformer were supplying load to the Safety Related buses, the bus voltages for the above range of 345 Kv Substation voltage with 1AR carrying 7500Kva would be as follows:

354 KV 338 KV I

4.16 KV Bus 15 4081 3872 4.16 KV Bus 16 4081 3872 480v L.C. 103 449 422 480v L.C.104 447 420 1.c.

With the station auxiliaries and therefore the safety related buses, supplied by 1R Transfomer the lowest voltage will occur on the safety related buses when the 115 Ky Substation voltage is at the minimum nomal operating voltage of 118 Ky and 1R Transfomer is carrying the station auxiliary load of 32 Mva.

4.16 KV Bus 15 4155 4.16 Kv Bus 16 4100 480v L.C.103 458 480v L.C. 104 449 The highest voltage will occur on the safety related buses when the station auxiliaries are supplied by 1R Transfomer under no load con-ditions and the 115 Kv Substation voltage is a maximum nomal opera-ting voltage of 125 Kv.

4.16 KV Bus 15 4629 4.16 Ky Bus 16 4629 480v L.C. 103 534 480v L.C. 104 534

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- - -.. ~.. -. -

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i For the case of 1AR Transformer supplying the safety related buses the lowest voltage condition on 4.16 Ky buses will occur with 1AR loaded at 7500 Kva and 345 KV bus voltage at 338 Ky.

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4.16 Ky Bus 15 3872 4.16 Ky Bus 16 3872 480v L.C.

103 422 480v L.C.

104 420 For the other extreme, no load on IAR and 345 Ky bus voltage as 354Kv:

4.16 Kv Bus 15 4210 4.16 Ky Bus 16 4210 480v L.C. 103 486 f

480v L.C. 104 486 i

Our design is presently being analyzed to determine if the voltage profiles at the safety related buses are satisfactory.

1.d.

The generator voltage operating range is limited by machine design and therefore operating practice to 22 Ky + 5%. The station auxil-iaries bus voltages are therefore not detemined by 345 Ky Substation voltage when the station auxiliary buses are supplied by 11 Station i

Aux. Transformer. The range of station auxiliary (safety related) bus voltages occurring with 11 station auxiliary transfomer carrying 30.4 bWA are as follows:

23.1 KV 20.9 Kv

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4.16 Ky Bus 15 4350 4040 l

4.16 Ky Bus 16 4300 3900 480v L.C. 103 480 450 480v L.C. 104 480 442 1.e.

There are two loss of voltage trip sensors located on each of the i

two safety related buses. The trip setpoint for these sensors is 2.625 Kv. The trip setpoint selection was based on the stall volt-l age of the motors fed by the bus.

1.f.

With the station aux. buses supplied by 1R Transformer, the maximum 4.16 Ky and 480v bus voltage will occur with 115 Kv Substation volt-age at 125 Kv. The following bus voltages will occur with 1R trans-former carrying 32 hWA:

4.16 Ky Bus 15 4400 l

4.16 KV Bus 16 4350 480v L.C. 103 483 480v L.C. 104 477 l

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With 1AR supplying the safety related buses the maximum 4.16 Ky ard 480v bus volts will occur when the 345 Kv bus is at 354 Kv:

j No load Full load 1

4.16 av Bus 15 4210 4081 4.16 Ky Bus 16 4210 4081 480v L.C.103 486 447 480v L.C.104 486 449 The loss of voltage relays are all set to drop out at a 4.16 Ky bus voltage of 2.625 Kv. The corresponding 4.16 Ky and 480v bus volt-age at the time of drop out will be:

4.16 KV Dus 15 2.625 Ky 4.16 Ky Bus 16 2.625 KV 480v L.C. 103 286 V 1

480v L.C. 104 287 V 1.g.

No station auxiliary motors or contactors will operate correctly at the voltages corresponding to drop out of the loss of voltage relays.

A definition of the voltage range over which the safety related components, and non safety components can operate continuously in the performance of their design function will be supplied follow-ing completion of the analysis discussed in 1.c.

above.

1.h.

The Operators take a voltage readings of each 4.16 Ky bus (excluding discharge structure buses) every hour from voltage monitors located in the control room. The computer provides an alarm at a high volt-age of 4.5 KV and at a low voltage of 3.8 KV on any of the 4.16 KV buses. A trend recorder monitors 345 Ky and 115 Ky bus voltages.

An annunciator alanns for loss of voltage in the 345 KV or 115 Kv Substation. There are also voltage indicators for the main genera-tor, diesel generators and 1AR transformer.

2. The load shedding feature is not maintained after the diesel genera-l tors are connected to their safety related buses.

3. There is no grid stability analysis cited in the FSAR, however the following operating limits have been established:

l a.

Real 6 reactive power - see attached figure.

l b.

Generator voltage -

.2 KV + 5%.

c.

Frequency - underfrequency trip at 58.5 hertz.

l Operating procedures outline these limits and provide instructions for making necessary adjustments.

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3-A.

A description of any proposed actions or modifications to our facility will be provided following ccupletion of the analysis discussed in 1 c.

above.

Yours very truly, 3r'd.

v L. O. Mayer, hhnager, Nucicar Support Services IDt/sdd Attachment ec:

J. G. Keppler G. Charnoff MPCA Attn:

J. W. Ferman I

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