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*'"""I'NRC Dl,STRIBUTION FOn PART 50 DOCKET MATERIAL

TO: J.F. STOLZ FROM: TOLEDO EDISON DATE OF DOCUMENT

TOLEDO, CHIO 11-3-76.

L.E. ROE oATE RECEivEo

11-10-76

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(E C RIGiN AL {]UNC LASSIPIE DOCOPY 1

DEScrlPTION ENCLOSU RE

LTR. RE. OUR 10-1-76 LTR.., TRANS THE FOLLOW- RESULTS OF INVESTIGATION OF THE'JEFFECTS OF GRI:IING.... VOLTAGE W...

( 1 SIGNED CY. RECEIVED).. ...( . 7..PAGES)-. .

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__JLANT NAME: DAVIS BESSE y-. , ,

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SAFETY FOR ACTION /INFORMATION E?NTRn SAB 11-12-76

ASSICNED AD: A_SSIGNED AQr/ BRANCH CHIEF: STOLZ BRANrH cMTEP. l

IPROJECT MANAGER: PROJECT MANAGER *.

Ii / LIC. ASST.: HYLTON LIC. ASST.!

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PROJECT MANAGEMENT REACTOR SAFETY OPERATING TECH. CAMMTTL'

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EDISON

November 3, 1976 LOWELL E. ROEv.c. m..o.at

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Serial No. 144 mei ass.s 4afv ss

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Mr. John F. Stol.: 3'

Chief Light Water Reactors 9/ Cu,s.eg.;,.;7.d.

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naC ;.swBranch No. 1 Division of -

Project Management ;,

United States Nuclear Regulatory CommissionWashington, D.C. 20555 :,p

Dear Mr. Stols:

Your letter to us dated October 1,1976, described equipment failuresduring a degraded grid voltage condition at Millstone, Unit 2. We haveanalyzed per the request for information in your Enclosure 2 the effectof various grid voltage conditions on Davis-Besse Unit No. 1. A summaryof this investigation is included in Attachment 1 of this letter.

Yours very truly,

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Attachment 1 - Results of investigation of effects of grid voltageon Davis-Besse Unit No. 1

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THE TOLEDO EDISON COMPANY EDISON PLAZA 300 MACISON AVENUE TOLEDO. CHIO 43652

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ATTAC19EENT 1 - RESULTS OF INVESTIGATION OF EFFECTS- 0F GRID VOLTAGE ON DAVIS-BESSE UNIT NO.1

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Describe the plant conditions under which the plant auxiliary systems(safety related and non-safety related) will be supplied by offsitepower. Include an estimate of the fraction of normal plant operatingtime in which this is the case.

Response: Normal occurrences for which plant auxiliary systemsare supplied from offsite power include plant startupand shutdown. Presently the one month refueling opera-tion per year is the only planned occurrence.

Abnormal occurrences.for which plant auxiliary systemsare cupplied from offsite power include faults associatedwith the auxiliary transformer. No time estimate isavailable for abnormal occurrences.

Item Ib

The voltage used to describe the grid distribution system is usuallya " nominal" value. Define the normal operating range of your gridsystem voltage and the corresponding voltage values at the safety re-lated buses.

Response: Tha normal operating range for the grid system voltageand the corresponding voltage values at the safety re-lated buses are given below:

Minimum Voltage Maximum Voltage

345 KV Grid 98.3% 102.2%4.16 KV 96.6% 101.1%

480 V 94.7% 99.3%

Item Ic

The transformers utilized in power systems for providing the requiredvoltage at the various system distribution levels are normally providedwith taps to allow voltage adjustment. Provide the results of an analysisof your design to determine if the voltage profiles at the safety relatedbuses are satisfactory for the full load and no load conditions on thesystem and the range of grid voltage.

Response: Voltage profiles are listed below for the full loadand no load conditions.

System Voltage

98.3% 102.2% 98.3% 102.2%

Bus Full Load No Load

4.16 KV 96.6% 101.1% 102.8% 106.9%480 V. 94.7% 99.5% 105.0% 109.3%

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* At no load and 102.2% voltage of the grid, the calculated bus voltages-are above the allowable voltages for some of the equipment-as listed initem ig. Therefore, when the unit is shut down, administrative pro-cedures will be taken to lower the, voltages to within acceptable limits.

Item Id

Assuming the facility auxiliary loads are being carried by the stationgenerator, provide the voltage profiles at the safety buses for gridvoltage at the normal maximum value, the normal minimum value, and atthe degraded conditions (high or low voltage, current, etc.) which wouldrequire generator trip.,

Response: When Davis-Besse Unit No. I auxiliary loads are carried-

by the station generator, the voltage profiles at thesafety buses are as follows:

Minimum Voltage Maximum Voltage,

345 KV Grid 101.7% 102.1%4.16 KV 100.0% 97.1%480 V 98.5% 95.3%

At degraded conditions below the minimum voltages listed above,system load shedding of 10% will occur at 59.3 Hz and 15% at 58.9nl. If degradation continues, i.e., 58.2 Hz for 30 cycles, thegenerator breaker is tripped, the grid load is disconnected and thegenerator supplies the station auxiliaries at the generator nominalvoltage.

On overload conditions, the system can operate with the generatorvoltage down to 95% continuously, i.e., 23.75KV. The calculatedcorresponding voltages on the 4.16KV and 480V safety related busesare 92.8% and 90.7%, respectively.

Item le

Identify the sensor location and provide the trip setpoint for yourfacility's loss of Offsite Power (undervoltage trip) instrumentation.Include the basis for your trip setpoint selection.

Response: Undervoltage relays are located at the safety related4.16KV buses with a setting'of 59% of rated voltage.This setting is predicated on total Loss of OffsitePower, but not on a sustained low voltage conditions.

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Item if.

Assuming operation on offsite power and degradation of the grid systemvoltage, provide the voltage values at the safety related bus,s corres-ponding to the maximum value'of grid voltage and the degraded gridvoltage corresponding to the undervoltage trip setpoint.

Response: The voltage values at the safety buses corresponding tothe maximum value of grid voltage are 101.1% on the4.16KV and 99.5% on the 480V. The calculated grid voltagecorresponding to the,undervoltage trip setpoint is 67%.

Question lg

Utilizing the safety related bus voltage values identified in (f),evaluate the capability of all safety related loads, including relatedcontrol circuitry and instrumentation, to perform their safety functions.Include a definition of the voltage range over which the safety relatedcomponents, and non-safety components, can operate continuously in thefarformance of their design function.

'

Response: The voltage range over which safety and non-safety relatedequipment can operate continuously in the performance oftheir design function is tabulated below:

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Equipment Rating

110%Non-safety related motors 90% -

Safety related motors * 90% - 110%,

Non-safety related 13.8KV Switchgear 83% - 109%!

Non-safety related 4.16KV Switchgear '3% - 114%>

Safety.related 4.16KV Switchgear 93% - 114%Safety and-Non-safety 480V Switchgear maximum of 106%

120V Contactors 80% - 110%120V Relays 95% 110%-

* Safety related motors are designed to start at 70% voltage and toprovide full load torque during a momentary dip to 65% of ratedmotor nameplate. voltage at the motor terminals for 15 seconds.

Item lh

Describe the bus voltage monitoring and abnormal voltage alarms availablein the control room.

Response: Voltmeters 'qc.ated in the Control Room provide theoperators with the voltage monitoring of the 345 KV,13.8KV, 4.16KV and 480V buses.

In addition, undervoltage conditions on the above busesare detected by undervoltage relays and alarmed on theannunciator and computer. Analog voltage signals from !

the two 345 KV buses and the two essential 4.16 KV buses |

!are' logged hourly. |

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,EItem 2

The functional safety requirement of the undervoltage trip is to detectthe loss of offsite (preferred) power system voltage and initiate thenecessary actions required to transfer-safety related buses to theonsite power system. Describe the load shedding feature of your design

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. (required ' prior to transferring to the onsite (diesel generator) systems)and the capability of the onsite system to perform their function if theload shedding feature is maintained af ter the diesel generators areconnected to their respective safety buses. Describe the bases (if any)for retention or reinstatement of the load shedding furetion'after the

diesel generators are coanected to their respective buses.

Response: If loss of power is confirmed by loss ot voltage atthe safety related 4.16KV bus, the following occurs:

1. All bus load breakers, except the breakers supplyingpower to the 480V safety related switchgear andcomponent cooling pumps, are tripped.

2. Both source breakers are tripped and the bus isisolated.

3. The emergency diesel generator associated with thedeenergized bus starts, the generator breaker closes,and the service water pump utarts after a timedelay.

This operation occurs anytime an undervoltage conditionexists on the bus. However, analysis has shown that thelowest voltage occurring on the bus during sequentialloading of the diesel generator is about 78%. Therefore,.

since 59% voltage is required to initiate in-plant loadshedding, load shedding does not interfere with theoperation of the onsite system.

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Item 3

Define the facility operating limits (real and reactive power, voltage,frequency and other) established by the grid stability analyses cited inthe FSAR. Describe the operating procedures or other provisions presentlyin effect for assuring that your facility is being operated within theselimits.

Response: The stability analysis cited in the FSAR for Davis-Besse Unit #1 determined an unstable condition resultingfrom a fault that left the station tied to the system viaonly the Ohio Edison line. This line was one of threenormally available. One result of this study was the

! addition of a fifth breaker to the switchyard in such away. that no single electrical fault lef t the station,

connected to just the Ohio Edison line.

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, Item 2

The functional safety requirement of the undervoltage trip is to detecttha loss of offsite (preferred) power system voltage and initiate thenecessary actions required to transfer safety related buses to theonsite power system. Describe the load shedding feature of your design

. (required prior to transferring to the onsite (diesel generator) aystems)d and~ the capability of the onsite system to perform their function if theU load shedding feature is maintained af ter the diesel generators are!! connected to their respective safety buses. Describe the bases (if any)

! for retention or reinstatement of the load shedding function after the

| diesel generators are connected to their respective buses.;!

Lesponse: If loss of power is confirmed by loss of voltage atthe safety related 4.16KV bus, the following occurs:

1. All bus load breakers, except the breakers supplying'

power to the 480V safety related switchgear and;;component cooling pumps, are tripped.

2. Both source breakers are tripped and the bus isisolated.

3. The emergency diesel generator associated with the;

deenergized bus starts, the generator breaker closes,and the service water pump starts af ter a timedelay.

;.

This operation occurs ar,cime an undervoltage conditionexists on the bus. Eowever, analysis has shown that thelowest voltage occurring on the bus during sequentialloading of the diesel generator is about 78%. Therefore,since 597. voltage is required to initiate in-plant loadshedding, load shedding does not interfere with theoperation of the onsite system.

Item 3

! Define the facility operating limits (real and reactive power, voltage,frequency and other) established by the grid stability analyses cited inthe FSAR. Describe the operating procedures or other provisions presently ,

in effect for assuring that your facility is being operated within these |

!! limits.,

Response: The stability analysis cited in the FSAR for Davis-,, Besse Unit #1 determined an unstable condition resulting

1

fran a fault that lef t the station tied to the system via

); only the Ohio Edison line. Ihis line was one of threenormally available. One result of.this study was theaddition of a fif th breaker to the switchyard in such a'

way that no single electrical fault left the station

i- connected to just the Ohio Edison line.

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There are presently no transient stability considerationswhich restrict real and reactive power, voltage, and

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frequency of the unit beyond the limitations set by themanufacturer. Manufacturer's limitations are appro-priately identif'04 in station operating procedures.

Item 4

Provide a description of any proposed actions or' modifications to yourfacility based on the results of the analyses performed in response toitems 1-3 above.

Response: We propose to extend the protective system to coverthe conditions established by our response to items 1-3.The feasibility of extending the protection is now underin-depth study. We will submit the final proposals nolater than December 31, 1976.

pc 33a/2-6

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