ML17174A104

Forwards Info Re Adequacy of Electric Distribution Sys Voltages,In Response to NRC 790808 Request.Addl Info Re Evaluation of 480-volt Undervoltage Conditions Will Be Provided by 791215

ML17174A104
Person / Time
Site:	Dresden, Quad Cities, Zion
Issue date:	11/01/1979
From:	Janecek R COMMONWEALTH EDISON CO.
To:	Gammill W Office of Nuclear Reactor Regulation
References
NUDOCS 7911060330
Download: ML17174A104 (26)

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Commonwealth Edison One F1rs1 Na11ona1 Plaza. Chicago. Illinois A*aares5Reiifv1o: P-651 0tiice-80X:7st Chicago. Illinois 60690 November 1, 1979 Mr. William Gammill, Acting Assistant Director for Operating Reactors Projects Division of Operating Reactors U.S. Nuclear.Regulation Commission Washington, D.C.

20555

Subject:

Dresden Station Units 1, 2, and 3 Quad-Cities Station Units 1 and 2 Zion Station Unit& 1 and 2 Adequacy of Station Electric Distribution System Voltages NRC Docket Nos. 50-10/237/249, 50-254/265 and 50-295/304 References (a): w. P. Gammill letter to All Power Reactor Licensees dated August ~,

1979 (b):

R. F. Janecek letter to W. Gammill dated October 91 1979 I

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• Co. is reviewing the adequacy of the Dresden,.Quad-Cities,**

L_.. _._ *-*--------~and.. Zion -Station.. auxiliary.power _~ys~e1q_s.

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b- * * * *... :...,~..:~.:.;.,~~~Reference ~b},-.c~e.,are ~submitting..::repoJ.ts :;wb.ich:~~Qn_cern:~tbe -~~-.::'.::---_=.:::;,--~~:!,".:.:: ~ -:.:

p-,*==* * *:-;~'-::**:~~":'.~~=-~4'cadequacy ;of -~the* :el.ectfic distr.ibutlori-Z~y~J"tem :::=.vo*1ta9es... ::and. ;_';~-~---~-=~::::~~~;:;~~::?,~--~'.*;.,: -~~-

?;,,,.. ~. *-*----* ~---~-. -~ :.:....,aescr ibes.. the results of.. our.analy,sis ~of.;.the.. auxiliary;:;power -_* :.

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systems.

These reports are contained in Enclosures 1, 2 1 and 3 for Dresden 2/3, Quad-Cities, and Zion, respectively.

The analysis for Dresden Unit 1 will be submitted by February 1,

1980, As stated in the reports, additional information concerning further evaluation of 480 volt under-voltage conditions will be provided by December 15, 1979.

Please address any additional questions you may have concerning this matter to this office.

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I*

.Mr. William Gammill:

Commonwealth Edison 2 -

November 1, 1979 One (1) signed original and seventy-nine (79) copies of this transmi~tal are provided for your us~.

RFJ:mae enclosures

~

Very truly yours,

• R(:f;;[ t!::::!

Nuclear Licensing Administrator Boiling Water Reactors

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Adequacy of Station Electric Distribution System Voltages Cormnonwealth Edison Company Dresden Uni ts 2/3

.October 29, 1979

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.I plant's loads.

voltage Dresden Unit 2/3 Tbe NRC has required the licensees of power reactors to show that each station auxiliary power system will provide adequate power to essential Specifically, the licensee is asked to confirm the acceptability of the conditions on tpe station electric distribution systems with regard to:

1. Potential overloading due to transfers of either safety or non-safety loads.

2.

Adequacy of the offsite and the onsite distribution system to automatically start as wel~ as operate all required safety.loads.

Each generating unit at Dresden 2/3 Station has a system auxiliary power transformer (SAT) which is supplied from the offsite power system.

Eac;i!J. SAT has capacity_ t_o... carr_y all the normal auxiliary power needs of one unit and the emer-gency *auxiliary _power needs of the second uirl.t.

Each. of these auxiliary power sU.ppiie*s--.fs. available-; -through circuit breaker switching' only to emergency equip-ment of the other unit. It has been verified that a single SAT is never required to carry all the auxiliary power loading for both units. There is no automatic circuitry or protective relaying failuxes that could cause one SAT to carry or at-tempt to carry all the auxiliary power load for both units.

See the figures of auxiliary power bus arrangements in Attachment B.

Attachment A provides an analysis of the Dresden 2/3 Station auxiliary power system voltages assumi..Tlg the SAT is loaded simultaneously with the maximum e~-pected loading on the auxiliary power system, plus the load of the engineered safety features.

The 11Guidelines for Voltage Drop Calculations" in Enclosure 2 of the NRC letter dated August 8, 1979 were followed in making this analysis.

Attachment B provides a r~view of the electric power system to the re-quirements of GDC-17.

AB indicated in Attachment A, the performance of the auxiliary power sys-*

tem at the 4K.V level is adequate.

The 480 volt Engineered Safety Featill-e (-ESF). ::::;:;~::=;-~~-~::"'.

buses rm:J. with a slightly high voltage for the maximum expected grid voltage of

=-*142KV for Unit 2 and J62KV for Unit ;.

C.E.Co.--.is presently-in the process.. of

• • • -~----*"~'"-"~

--..,-~~~--~-* __ evaluating the effect of _short duration overvolta,ge. ~~mdi tions _an~ v.rhat correct:i,v~ -~*.:~--~.~"--;-~~~

actions may be required.

This information will be provided by December 15, 1979.

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A test shall be performed to verify that the analysis program used to* -~*

make the calculations in Attachment A is valid.

The test will be made with 'the *----*--~**

output of both units disconnected from the grid which results in the minimum ex-pected voltage at the time of the test.

The minimum expected voltage at the time of the test is based on the grid system loading at that time, and will not neces-sarily correspond to the minimum grid voltage used iil the analysis of Attachment A.

The test will consist of measuring and recording the 345KV or 138KV, 4KV 2nd 480 volt bus voltages and the various bus loadings.

The grid voltage (345 or 138KV) and tbe bus loadings will then be used to calculate the various bus voltages using the same analysis progr3Ill used in me.king the calculations for Attachment A.

If the calculated results compare reasonably well with the measured bus voltages, tah.""i...-rig into acc~unt metering inaccuracies, etc., this will be considered to be verification of the analysis program.

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The test will be made at the first ti.me.that both units at the plant a.re disconnected from the grid at the same ti.me.

Test results will be submitted three weeks after the test is complete.

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SARGENT Be LUNDY ENGINEERS CHICAGO Project No. 6030-31 October 31, 1979

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.Attachment A l

ADEQUACY OF STATION ELECTRICAL DISTRIBUTION SYSTEMS VOLTAGES

-*-DRESDEN UNITS 2 & 3 I.

INTRODU~TION II.

The Nuclear Regulatory Commission (NRC) has required the licensees of all power reactors, in a letter dated August 8, 1979, to show that each plant's station auxiliary system will provide an adequate supply of power to essential loads during the contingency which presents the largest load demand on the auxiliary system.

This request was a result of the incident at Arkansas Nuclear One Station described in detail in the NRC's IE Information Notice 79-04.

This report documents the results of a study conducted to determine the adequacy of the electrical auxiliary system at the Dresden Nuclear Station Units 2 and 3 to provide a pow~r source of sufficient capacity and capability to supply the ~ngineered safety feature loads iQ the event of a con-tingency presenting the maximum load demand on the system.

The result of the study for Dresden Unit 1 will be furnished later.

Dresden Unit 1 is presently out of service.

. -OFFSITE POWER SUPPLY

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'.**The offsite power at Dresden Unit 2 is provided from CECO 138 kV system (blue bus).

The voltage at this high volta~e

_:-*bus varies 'from 132.to 142 kV: '1he -short_;c1rcuit level**:.ranges:::::::::-* --:::::-*:.:::

-from -1945--::'.°to --15000 -MVA.

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._The. off site power.:at )'.>resden ~unit -:3.:=;is.*provided.:from.;eECO_:~::i':

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345 kV **system (red *bus) *. The voltage at this :high,.voltage.... :..::.:.::E;.~~~=*-+:,\\~~::;~

• bus varies from 344 to 362.kV.

The short circuit level ranges from 6275 to 25000 MVA.

The switchyard arrangement at Dresden.Nuclear Station is shown on F i.gure 1.

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SARGENT & LUNDY ENGINEERS CMICACilO October 31, 1979 60~0-31 Page 2

• The station auxiliaries for each of these two units are

~-,---~*----*-A*******~-.. --~---*--served from s~i-X, 4.16 kV buses, : two of whieh are designated for safety-related loads.* The electrical distribution system at Dresden Nuclear Station is shown on Figure 2.

During no~al operation, half the station load is supplied from the' unit auxiliary transformer (UAT) and the other half from.the reserve auxiliary transformer (RAT).

When the generator is not operating, as during start-up or shutdown, or unit trip, the loads fed from the UAT are transferred to the RAT.

The unit's RAT is the first offsite source to the safety-related buses.

The RAT of the other unit is the second offsite source tlirough a bus tie provided between corresponding safety-related buses of the two units.

The interuni t tie is closed only if off site power to one of the two units is lost.

In accordance with Regulatory Guide 1.81, it is assumed that the other unit is either running or in a safe shutdown condition.

III.

LOADING ANALYSIS The auxiliary systems of the two generating units under study are connected directly through their -RATs to different

.high voltage systems.

The RATs of the two uni ts are, therefore., electrically independent.

The loading on one

.. ':Unit's auxiliary system will have no effect on* :the *performance

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- -unit analysis required by *the -guideline "is ~'.not**appli..cable-::t::7_:~:7"'.~:~'.*"':c:7&

in this.case.

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~"The worst loading condition *for "Units "2 -:and**3-*.rexists *'*when*'::'~~,,* *~,;.,-~.:;;_-:~~~_;;~~.;_"'

the unit experiences a loss of coolant accident.

The unit was supposed to be generating rated output.at the time of the event.

In addition to the ESF loads required during LOCA, all loads operating fqr unit's 100% ge'neration condition wer*e assumed to operate from RATs with the exception of:

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• e SARGENT & LUNDY

• ENGINEERS CHICAGO l~

Two Recirc. Pump MG Set Motors *

... 2. *. Two Reactor Cleanup Recirc. Pumps

3.

One Reactor Building Cooling Water Pump.

October 31, 1979 6030-31 Page* 3 These motors are tripped off at the instant of loss of coolant~accident.

Bus loadin9 assumed for the study is shown on Table 1.

• .IV.

CRITERIA FOR ACCEPTABLE VOLTAGE The criteria for the acceptable-voltage range at motors, con tac tors, and control circuits is based on equipment ratings as *defined by the National Electric Manufacturers Association.

These standards require that the maximum voltage should be limited to 110% of equipment rated voltage and the minimum voltage to be limited to.90% of equipment rated voltage.

• v.

In.order to _provide adequate torque for motor starting and to prevent contactors from dropping out at 480V motor control centers, the starting voltage should be limited to an acceptabl_e level. This level is 75% of motor rated vol ta.qe.

• SYSTEM PERFORMANCE

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. ;~:~~.:.~~-. -.:_*,* -L-~-;-~~1-tage *"analysi's --was -*made ~£or ;'.Units. :2 :~and -~3 :::RATs*-~:ar~ylrtg :~=*::~~:~:*~l~~~;~

• ,their ~orst case loading.

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=-~~:-::::--:~".:":.~*-:*=*-*~:~=:':The ~-ifupeaances --of,cables-between.'tlie*-.£.oiiowing :~buses*::;~r--e*=-=.::::-..~=::::::::;-'.";:_~".'

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• 3.

4160V Buses 33 and 33-1

4.

4160V Buses 34 and 34-1 for Unit 3 The minimum calculated running voltages on the various buses of Units 2 and 3 are shown in Figures 3 and 4, respectively.

~*..

SARGENT & LUNDY ENGINEERS CHICAGIO Dresden unit 2 (October I,6030-31

Page 4 31, 1979 The results of voltage drop caiculations -show that the voltage at the 4 kV buses are satisfactory.

The minimum running 3786 voltage is 91.0% of 4.16 kV or 94.6% of 4 kV.

This a.llow for enough margin to account for voltage drop in the motor feeder *. A ~% drop iri voltage 1s a typical value for a motor feeder cable at 4 kV level.

In making the calculations, the minimum value of switchyard voltage and the minimum value of switchyard short circuit current were assumed.

The running voltages at selected loads are shown. in Table 2.

These values do not include voltage drop in the cables from the bus to the load.

The loads selected are those expected to have *the maximu...'Tl voltage drop from the bus to the

.. equipment. terminals.

The starting bus voltages are also shown in Figure 3.

The minimum starting voltage is 3156V ( 78. 9% of. 4000V) when a 900*0 horsepower. reactor feed pump is started on bus 21 or

22.

This value is considered acceptable.

The starting voltage *for the other 4 kV motors is above/80% of motor rated voltage.

Simulation was made to start all ESF motors at once and it was found that the voltage is better than 80% of motor rated voltage.

The total horsepower of all

• *ESF motors simultaneously starting in the event of LOCA

. _;£through *one RAT winding are about 4600 horsepower.

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Figure* 3 also indicates that voltage at 480V buses are

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• • • -:Satisfactory with unit substations set *at ~4ossv*.:i ~2~%) ~:~:::~--=-=-~=-..:.=_::-:-:*.--:-.,.,_--...... "*

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___ This_.*2~%.. boost can.result -in-maximum :.v0l-tages ~in-excess.. '....,,,;-;

.of 110%.of motor J:"ated voltages* if.J:he _tr.an~fo~~r ~s _15=:g?.J~1Y.~... *.~~::~~.-.,;;,.:~;~

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• ~**on Table 3.. The minimum voltage at 4 80V -switchgear *bus is 429V or 93.3% of 460V.

The minimum voltage at the switchgear

• a.llows for a 3.3% drop in cable between 480V switchgear and 460V motor.

A 3.2% drop in voltage has been calculated for a cable between~V switchgear and 460V motor terminal.

This cable was expected to h~ve the maximum voltage drop.

SARGENT 8c LUNDY ENGINEERS CHICA~

Dresden Unit 3 October 31, 1979 6030-31 Page 5 The result of the volta.ge drop calculations is shown on Figure 4~

These results indicate that the minimum auxiliary system ~oltages for Unit 3 are generally 2% higher than those for Unit 2.

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4 VI.

UNDERVOLTAGE RELAYS

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• ",*T-:-~-T"*------ * - 0 Undervoltage relays are provided for each ESF.bus* to transfer the ESF load to the onsite diesel generator in case offsite power is lost or degraded.

The. minimum voltage to transfer load to the ESF buses is 2929V or 73.0% of 4000V.

Since the miniinum expected voltage during normal motor starting operation, 3578V, is well.above the relay setting, transfer to the onsite power supply should not occur.

The undervoltage relays incor-porate sufficient time delay so that short circuits can be cleared without undervoltage relay operation.

H. Ashrafi

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ENGINEERS

• SARGENT & LUNDY CHICAGO TABLE 1 BUS LOADINGS ASSUMED FOR OFFSITE POWER SUPPLY ANALYSTS DreS!den Unit 2 Bus*

41,60V Bus 4160V Bus 4160V Bus 4160V Bus 21 + 22 23 + 24 23-1 24-1 Load

. 14.9 MVA 2.5 MVA 2.8. MVA

34. 7 MVA B.

• Dresden Unit 3 Bus Load 4160V Bus 31 + 32

• 14. 5 MVA 416ov* Bus 3~ + 34

15. 7 MVA

. *.. mov Jlus.. 3 3-1 _... *.... *.

-,,----~ _ ' +2_::5.}v~~e:. - ~~'.-.. :..~~;;~1 41*60V Bus 34-1

... ( 3. 5 MVA'\\

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TABLE 2 Rh~ING 1~0LTAGES AT SELECTED LOADS Load HP Unit 2 i

Reactor Feed Pump 9600 Circulating Water Pump * ** *

l.~50 Service Water Pump

iboo Core Spray Pump LPCI Pump RX Bldg. Exhaust Fan aoo ;

.J :~oo. :jl:

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I *100.l.*

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t:r Feed Pump*

II*! ! 9boo :I

• Circulating Water Pum~* j1 1

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j i~sb *i

~ * ~*1*.d 'l ii J... !

Service Water Pump

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.1 1**.:.*

core Spray Pump Y!il::i: j !~oo

• LPCI Pump

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1 1 ?oo !

I 111 RX Bldg. Exhaust Fan f~'.'.{'j' *: j: ;Joo: !

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Rated Voltage (vol ts) 4000 4000 4000 4000 4000

'460 4000 4000 4000 4000 4000 460 Running Volts 3913 3800 3800 3786 3786 429 4027 3876 3876 385.8 3858 438 Percent of Motor' *'

Ra1;ed 97.9 95.0 95.0 94.6 94.6 93.3 100.7 96.9 96.9 96.4 96.4 95.2

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4SOV 4SOV Bus e

21 + 22 23 + 24 23 + 24' 24-1 24-1 Swgr Bus 129 31 +* 32 33 + 3.4 e

33 + 34 34-1.

34-1 Swgr Bus 139..

SARGENT & LUNDY ENGINEERS.

CHtCAGO

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TABLE 3 NO-LOAD VOLTAGES-DRESDEN UNIT 2 Percent of

____..... __,~.. -*

l.

Bus Switchyard 4.16 kV Buses Unit Substations Fed From 4.16 kV No-Load Volts 142 I 000 4,390 519.7

. Equipment Rating 109.7 113.0 NO-LOAD VOLTAGES-DRESDEN UNIT 3 Bus

.. _Swi tchya.rd

~-.16 kV Buses Unit Substations Fed From 4.16 kV AO(..,_'.,---*- *....-----*--* * -,-

No-Load Volts 362,000 4 '365.

516 Percent of Equipment Rating 109.0 112.3

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Attachment B Dresden Units 2 & 3 Review of Auxiliary Power Connections to Offsite Network INTRODUCTION The Commonwealth Edison Company offsite electrical power system connections to Dresden Station are designed to provide a diversity of reliable power sources which are physically and electrically isolated so that any single failure can affect only one source of supply and cannot propagate to alternate sources.

SYSTEM AUXILIARY POWER TRANSFORMERS Each unit has a system auxiliary power transformer which has sufficient capacity to handle the auxiliary power needs of one unit and emergency auxiliary equipment of the other unit.

Each of these auxiliary power supplies is available, through circuit breaker switching, to emergency auxiliary equipment of the other unit and therefore serves as the second offsite source for a unit.

This can be seen on Figure Dl and is in compliance with GDC~17.

UNIT 2 SYSTEM AUXILIARY NETWORK CONNECTION The Unit 2 system auxiliary transformer is connected to the offsite network in the 138Kv switchyard.

(See Figure D2).

The 138Kv bus is interconnected with eight sources of power, namely, Unit 1 output through its main power transformer, six 138Kv transmission lines, and a 300 MVA transformer.which connects to the 345Kv switch-yard.

Two of the 138Kv transmission lines are double circuited and.

terminate at Joliet Generating Station.

One of the lines terminates at both Will Co. Generating Station and at McCook Transmission Sub-station.

Of the other three lines, one terminates at Kewanee Transmission Substation, one at St~eator Transmission S~bstation,

• and one at Bradley Transmission Substation.

UNIT 3 SYSTEM AUXILIARY NETWORK CONNECTION The Unit 3 System Auxiliary Transf.ormer is connected to the offsi te network.in the 345Kv switchyard.

(See Figure D3).

The*345Kv double ring bus is interconnected with eight sources of power, namely, Unit 2 and Unit 3 outputs through their main power trans-formers, and six 345Kv transmission lines.

Two lines terminate at Goodings Grove Transmission Substation.

Two lines terminate at Electric.Junction Transmission Substation.

Of the other two lines, one terminates at Powerton Generating Station, the other at Pontiac Midpoint :rransmission Switching Station.

2 -

SYSTEM The twelve transmission lines which interconnect Dresden Station leave on three separate transmission corridors (See Figure D4) and then diverge to the Edison transmission network.

The pro-bability of losing the offsite electric power supply has been minimized by the design of the Commonwealth generation and transmission system.

Increased reliability is provided through interconnections to neighboring systems.

The Commonwealth trans-mission system consists, in part, of 74 345-kV lines totaling 2244 miles, and 3 765-kV lines totaling 152 miles.

The transmission system is interconnected with neighboring electric utilities over 28 tie lines:

12 at 138 kV, 15 at 345 kV, and 1 at* 765 kV.

Commonwealth is a member of Mid-America Interpool Network (MAIN).

In general, all electric utilities in Illinois, northern and eastern Missouri, Upper Michigan, and the eastern half of Wisconsin are members of MAIN.

The transmission within MAIN currently consists of 120 345-kV lines totaling 4714 miles and 3 765-kV lines totaling 152 miles.

The reliability of the transmission grid is demonstrated by the performance data of the 345-kV transmission lines.

The average 345~kV line in the MAIN grid experienced i.7 f9rced outages per year, with an average duration of 59 hours6.828704e-4 days <br />0.0164 hours <br />9.755291e-5 weeks <br />2.24495e-5 months <br /> per'forced outage during 1975 and 1976 covering 219 line years of exposure (References 1 and 2).

For the 12 years between January l, 1965, and. December 31, 1976, the average Commonwealth 345-kV line experienced 1.9 forced outages per year, with an average duration of 7.8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> per forced outage.

This 12-year period represents 427 line years of experience.

The causes of the forced line outages may be summarized as follows:

a.

terminal-related *

1.

storm damage

2.

equipment failure

3.

human error

4.

false trip

5.

other

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1.

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other c.. unknown

% of Forced Outages 3.4 18.4 7.3 13.7 14.5 17.5 3.0 13.7 8.5 100%

e 3 -

e The only source of fire or explosion in the area of the switch-yard would be the oil filled circuit breakers.

These circuit breakers are located so that the worst possible failure will not result in the total loss of offsite power.

The combined micro-wave and meteorological tower is located away from transmission lines and switchyards so that it cannot cause failure of the offsite sources.

The described design of the offsite power system is in compliance with NRC General Design Criterion 17.

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ATTACHMENT 3 138kV SUPPLY FOR DRESDEN TRANSFORMER 22 (Unit 2)

The reliability of supply to Dresden Transformer 22 from 138kV buses 1 and 3 has been evaluated by Commonwealth Edison's System Planning Department.

The results of that evaluation, summarized in the attached table, indicate that the reliability of supply to these two busses is essentially equal at approximately 0.05 outages per year.

Bus 3 will be somewhat less reliable, however, because of outages originating on Transformer 12 which is connected directly to Bus 3.

Since no directly applicable data on the reliability of such 138kV transformers is available, the frequency of outages on 345kV

• auxiliary transformers of 0.166 outages per year was used in estimating the overall reliability of Bus 3 (see table).

This value is considered to be substantially too pessimistic, perhaps two to five times higher than appropri-ate for Transformer 12.

A value of 0.035 to 0.083 outages per year would be more representative of Transformer 12's expected reliability.

Bus 3 is somewhat preferable to Bus 1 from the standpoint of voltage support for Transformer 22 during outages of other 138kV buses.

345/135kV auto-transformers are connected to Buses 2 and 4 and Bus 3 is directly connected to both, while Bus 1 is connected only to Bus 2.

Thus for a Bus 2 outage, Bus 1 will depend on 138kV lines from Joliet and LaSalle for its supply.

This analysis is based on 345kV equipment outage experience since 138kV outage data has not been compiled in a manner supporting probabilistic analysis.

Errors introduced by this assumption will generally be offset in comparing the reliability of Buses 1 and 3 as their connections are essentially symmetrical except for normally open bus tie 2-3.

outages of Transformer 22 itself are not included as they are common to either plan.

0859K

Attachment Stat1on ~2 Dresden Re11ab111tv of 138kV Supoly to Transformer 22 Supply Pr1mary Length Est. Outages Probab111ty Est. Outages From Outage

{miles}

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of Breaker of Supply Failure {1}

Bus per Year 0

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( l) Based on 345kV outage data presented 1n EPRI Report EL 3880, Vol. 1.

L1nes: 1.9 +.0254 L outages/yr., where L = length 1n m1les 56975(2)