ML19220B882

Forwards Addl Info Concerning Applicants Solution to Problem Involving Single Auxiliary Transformer Operation at TMI-2

ML19220B882
Person / Time
Site:	Crane
Issue date:	08/31/1978
From:	Herbein J Metropolitan Edison Co
To:	Varga S Office of Nuclear Reactor Regulation
References
GQL-1454, NUDOCS 7904270583
Download: ML19220B882 (20)

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l METROPOLITAN EDISON COMPANY :x:w.n ce wism ouuc uriuma cc ucur.=

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POST OFFICE BCX 542 REACING. PENNSY LVANI A 196C3 TELEPHONE 215 - 9r3.%01 4.,-,

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C;erating License No. DPE-73 Oceket No. 50-320

n respense to the request cf Mr. H. Silter of your staff, encicsed please find additional info mation concerning cur sclutica to the prcb'a icl ring single Auxiliar-/ Wansforner C;eration at

~'C-2.

' nis problem was initially repor ed to the NEC in Licensee Etent Report ( LZR) 78-35 /l"' on May 9, 19~S.

Additional info maticn concerning cur solution to this pctential problen was sut=itted to your office on May 30, 1978. As was indicated in that let-ter, our re'riev cf the problem, its solution, and GCC 17 leads as to the conclusion that cur solution (as described in the attachments to this let-ter) neets all the prc'risicns of GDC 17

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CORIENTS I

3ackgrcund Information II Autecatic Balance cf Plant Load Shedding (Description)

III Components Used IV Alternatives - Defeat of the Automatic Transfer Mechanism V

Compliance with General Design Criteria 17 VI Reliability Factors VII Su= mary and Conclusions O

I-Background Information On May 9,1973, Metropolitan Edison Company (Met-Ed) filed Licen ae Event Report (LER) 78-35/1T (see Attachment 1) with the Nuclear Regulato y Com=ission. LER 78-35/lT identified a potential problem involving the Auxiliary Transformers at TMI-2.

If one of the auxiliary transformers at IMI-2 were to fail, all station loads would be automatically transferred to the re=aining transformer. Using a voltage study prepared by Burns and Roe (the project Architect En ginee r), it was determined that with the of f-site grid voltage at the icwer end of its normal operating range, if the full unit load was carried by a single Auxiliary Transformer, losses in the system would produce voltage levels low enough to blow entrol fuses on ES components if these components were called on to start (as, for example, in the event that a LOCA would occur).

At that time, Mat-Ed proposed several possible solutions to the problem, including the long term solution finally agreed upon (i.e. selective Balance of Pl ant (BOP) load shedding).

On May 30, 7.978, Met-Ed submitted GQL 0961 (see Attachment 2) to the Co= mission. This letter further explained the Auxiliary Transformer situation s.t TMI-2, and also identified which of the corrective actions mentioned in LER 78-35 would be taken.

In determining the corrective action whichevould be =ost acceptable, Met-Ed attempted to locate NRC tegulations and guidance which may have been published concerning Auxiliary Transf ormer and associated problems. Using the guidance available (i.e. the TMI-2 FSAR, GDC 17 and Reg. Guide 1.6) and sound engineering judgement, Met-Ed selected th automatic shedding of selected 30P loads as the best solution to the TMI-2 Auxiliary Transformer problem.

As will be demonstrated later, the solution chosen =eets all the require-ments of GDC 17.

Recently, the Commission has raised several questions concerning the long term fix which was chosen and installed.

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'n'estinghouse Model M6-6 CO/CA C0/C3 C0/A3 HD/CA HD/C3 RD/A3 Transformer Lock-Cut Relays Electro-Switch Corp.

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All co=ponents used in the Automatic 30P Lead Shedding Sche =e are of the same quality as the off-site power syste (including the Auxiliary Trans f o r=e rs).

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VI Reliability Factors Recent discussions with ce=bers of the NRC staf f have indicated that the reliability of the Autc=atic BOP Load Shedding Sche =e is a primary area of concern. Met-Ed has tested this scheme and found it to operate reliably.

A number of factors contribute to the overall reliability of the sche =e.

A.

As was =entiened in Section II, any of six lock out relays per auxiliary transformer may initiate the s0P load tripping sequence.

In addition these six re.1ays not only initiate the 30P load tripping sequence, but also are used to open the creakers which energize the transfor=er. Therefore, the auxilidry transformer will become de-energized as a result of energizing a relay which is in turn used to initiate the BOP

.ad tripping sequence. Therefore, if the trans-for=er becomes de-e.

gized, the 30P. cad tripping sequence =ust be initiated.

3.

As has already been indicated, sae compon.Js used in the Automatic 30P Load Shedding Sche =e are all of industrial co==ercial quality.

Although these componeuts do.iot carry the same " pedigree" as do safety-grade co=penents, there is essentially no dif ference between these ec==ercial quality ce=ponents, and safety-grade components used elsewhere, in the industry. In addition, these components are located in areas which are not expected to see adverse environ = ental conditions (such as a LOCA environ =ent).

C.

In addition, at the first scheduled refueli ng outage a Solid State Undervoltage Protection Syste: (SSUVPS) will be installed. This SSLTPS will act as a "back-up" for the Automatic 30P Load Shedding Scheme. The SSUVPS will perfor= this back-up function by detecting the undervoltage condition which would lead to the blowing of control fuses on safety related components. When such an undervoltage condition is detected the SSUVPS will atte=pt first to transfer the load to the failed auxiliary transfor=er, because this will not be possible, the e=ergency loads will be supplied by the on-site pcwer sources.

D.

The reliability of the Autc=atic 30P Lead Shedding Sche =a is further enhanced at the present time by a =anual "back-up".

E=ergency Procedure 2202-2.8 requires, upon the loss of an auxiliary transf or er and the failure of the Automatic 30P Load shedding Sche =e, that the operator =anually trip the loads which the Aute=atic 30P Load Shedding Sche =e should have tripped.

In addition, Met-Ed has undertaken to determine quantatively, the reliability of the Autc=atic 30P Load Shedding Scheme which has been installed.

The worst design basis condition only exists when tha f cllowing events have occurred si=ultaneously:

1) An Auxiliary Transfor=er has failed,

2) The Aute=atic 30P Load Shedding Scheme has failed, and

3) A LOCA has occurred.

In order to determine the probability of these events occurring sicultaneously, the ter st=ultaneously =ust be defined. For the purpose of our calculations, events will be considered to have occurred si=ultaneously if they have occurred within the same one

=inute period.

[2I3 ~ [ ($5 The probability of a LOCA occuring (P ) is 10-4 per year (WASH 1400).

L The probability of a Auxiliary Transfor=er failing (P ) is 1.445 x 10-6 A

per hour (IEEE 500).

The probability of tae Automatic SOP Load Shedding Sche e f ailing (P ) is 3

3.88 x 10-" per hour (IEEE 500).

Che reliability of the Autocatic 30P Load Shedding Scheme has been deter =ined using the reliability valces of each component of the scheme.

ThEse reliability values have been taken frem the reconmended values found in IEEE Standard 500. The probabili;y of failure for the Automatic BOP Load Sh;dding Scheme was determined by assuming the f ailure probabilities for all components which would prevent the scheme from completing its function.

In addition no credit has been assumed for n tial operation of the sche =e.)

Because the three events menticned above =ust occur "st=ultaneously" each of these probabilities =ust be converted to probabilities on a. per minute basis and then factored together (one sinute is 1.9 x 10-6 ears and 1.66 x 10-2 hours).

PL = (10-4) (1.9 x 10-6) 1.9 x 10-10 per minute (1)

=

= (1.445 x 10-6) (1.66 x 10-2) 2.4 x 10-8 per minute (2)

PA PS = (3.88 x 10-4)

(1.66 x 10 2; 6.4 x 10-6 per ninute (3)

=

The probability of these events occurring simultaneously (P77) is:

P.

= (P, ) (P. ) (Pe)

= 2.91 x 10-23 oer minute (4)

This may be compared with the reliability of the off-site power system. Met-Ed has found that the probability (Poi of the off-site power grid decaying to the point at which off-site power could not be used to sitigate the consequences of a LOCA with two auxiliary transfor:ers in operation is 3 x 10-7 per year.

Because this would not be a probles unless a LCCA occurred "si=ultaneously", it cust be treated in the same manner as was the above-centioned situation.

P

= (10-4) (1.9 x 10-6) = 1.9 x 10-10 per minute (5) t P

= (3 x 10-7) (1.9 x 10-6) 5.7 x 10-13 per minute (6)

=

0 Pro = (P ) (Po) = 1.08 x 10-22 per minute (7) 2 As descastrated above the probability of a si=ultaneous 10CA, auxiliary transformer failure and Autn=atic BOP Load Shedding Scheme failure is less than the probability of airuitaneous loss of offsite power and LOCA by a factor of nearly h.

It is therefore concluded : hat the 3CP Lcad Shedding Schere dces not decrease the reliability of the offsite power syste. :n fact, because the Occurrence of a LCCA is c--~^n to bcth of the above calculaticns it can be e-4nated.

This vouli all:v a cct;arison cf the probability of lec:ang Offsite pcwer, with the probability :f the 'st=ultinecus" loss of an Auxiliary Tr2rsformer and the Autc atic 3CP Lcad Shedding Echeme.

- t <

Probability of loss of offsite pot.er P op = 5.7 x 10-13 per minute (8) t (EQ 46)

Probability of simultaneous loss of Auxiliary Transformer and loss of Automatic J0P Load Shedding Sche =e (".Q 42 and #3)

PAT BOP " (P ) (P ) = (2.4 x 10-8)

(6.4 x 10-6) - 1.3 x 10-13 (9)

A S

per minute Thus, the combination of the Auxiliary Trsnsformer and the 30P Load Shedding Scheme is less likely to fail and therefore does not decrease the reliability of the offsite power grid.

Because the of f site power system hc.s been f cund to be acceptably reliable for use as the preferred power source, the Automatic 30P Load Shedding Scheme is also acceptably reliable. Therefore, the reliability of the preferred power source is cot appreciably af f ected by the installed scheme.

CONSERVATISMS IN PRECEEDING ANALYSIS:

1.

The reliability of the Automatic 30e Load Shedding Sche =e resulting from iteus C and D above were not included in the determination of Ps.

2.

The failure of a component which cculd inhibit any portion of the 30P Load Shedding Scheme was considered to cause a complete f ailure of the Scheme, (i.e., no credit was taken for partial Scheme operation).

3.

The method for calculating PS (i.e. su= sir.g of individual co=ponent fai bre rates) yields more conservative results than would be expected for f ailures of the system as a whole).

6 3 7 C.9

VII Su==arv and Conclusiens As has been demonstrat id above, Metropolitan Edison Cocpany has acted responsibly in referencing the appropriate NRC guidance for meeting Electric Power Systems Design Criteria. All applicable NRC guidance (i.e. GOC 17 and Reg. Guide 1.6) are complied with by the installed auto =atic BCP Load Shedding Sche =e.

Therefore, as has been demonstrated through probability analyses, the current TMI-2 design is a.esptably reliable. Further, because all applicable design criteria are met, and bec':se the reliability of the pref erred power source is not appreciably dif ferent from that under which the plant was originally licensed, no Liccasing precedent is set.

For the reasons mentioned throughout this report, Metropolitan Edison Company concludes that the installation of the Autcmatic 30P Load Shedding i che=e does not involve an unreviewed safety question because:

1) the probability of occurrence or the censequences of an accident or =alfunction of equipment L:portant to safety previously evaluated are not increased; 2) the probability for an accident of a dif ferent type than has been previously analyzed is not created, and 3) the margin of safety as defined in the bases of the Technical Specifications is not redu ed.

Therefore, we believe that the automatic 30P I aad Sheddicg Scheme is the only solution which is required for the problem which was identified in LER 78-35/1T.

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.S B3 m.. rJ Condensate Pu=p and a Second Heater Drain Pu=p are also tripped prior to the starting of Auxiliary Cc=ponents which would be needed to =icigate a LOCA condition.

One result of tripping 30P loads is to increase the voltage level at the E3 buses.

(This is the reason the Auto =atic 3CP Load Shedding Scheme was selacted as a solution to the proble= which was identified in LER 73-35/lT). As was =entioned earlier in this report, if a LOCA was to occur concurrent with the loss of an Auxiliary Transfor=er, the operation of the Auta=atic BOP Load Shedding Scheme (i.e., the tripping of 8250 HP in 30P loads) raises the voltage level at the Auxiliary Cc=ponents wnich will in turn be needed to =itigate a LOCA condition sufficiently to prevent the blowing of control fuses on r. hose cc=penents. The tripping of those sa=e loads plus the additional 30P loads (i.e. the additional Heater Drain mad Ccndensate Pu=ps) as occurs during a normal unit shutdown, will result in higher voltage levels at the Auxiliary Co=penents which would be needed to =itigate a LOCA condition.

Thus, during a unit shutdcwn with a single Auxiliary Transfor=er operating, suf ficient 30P loads are tripped prior to the starting of those Auxiliary Cc=ponents which would be needed to =itigate a LOCA Condition. This then provides suf ficient voltage to assure that control fuses on those co=ponents would not be blown, and in turn ensures the required components would start in the event of a LOCA.

Therefore, in response to Mr. Tedesco's questi a, if one assumes that both an Auxiliary Transformer and the Auto =atic 30P Load Shedding Sche =e f ail si=ultaneously (a double failure with probability of occurrence of 1.3 x 10-13 per =inute (EQ #9) or 6.8 x 10-8 per year), the safe, nor=al shutdown of the unit is not i= paired.

In addition, should a LOCA occur while the unit is being shutdown, the proble= centicned in LER 78-35/lT would be eliminated at the point during the shutdown when sufficient 30P loads had beer ripped. This point would be reached when the 2 Circ 'a'ater Pu=ps are tripped, fo11owing the turbine trip.

Prior to that point in the shutdown, the failure of an Auxiliary Trans-former, concurrent with the f aflure of the Autc=atic 30P Load Shedding Sche =e and a LOCA vould produce the sa=e proble which was identified in LER 73-35/lT.

This triple failure, as de=onstrated earlier in this report, is, due to the reliability of our scheme, a highly unlikely occurrence.

(See Section VI Reliability Factors.)

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(.' METHOPOLITAN EDISON COMPANY

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POST OFFICE SOX 542 REACING, PENNSYLVANI A 19503 TELEPHcNE 215 - 929 3601 May 9, 1978 GO,L C890 Mr. 3. H. Grier, Director Offi:e of Ins?ecticn and hforcement Eegica I U. S. ?!uelea.r Regulatory Ccc.issien 631 Pa-k krenue T.ing of Prussia, Pennsylvania 19hC6 Zear Sir:

Three P.ile ! lan:1 !!uelear Staticn L'ait 2 (TIE-2) g' Operating License :ic. DPR-73 malesed please find Licensee Frent Report 78-35/1T vhich is subaitted in a::Or:iance with section 6.91.8.h of ce Technical Specifications.

Sincerely, c:

.!. c. '.,'~.i J. G. Herbein Vice President-Ocneration

.. -n..,.. c j g v.

-..s.

Scicsu c: LER 78-35/1T hriey Silver (?!30) 00 83.n

LICENSEE EVENT REFORT c '.iset r LM.<: l l

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(PtEA:E PAINT OR TY

.LL b6 RED INFOM.9 ATICU) lo I -l O! 0l 0l 01 Ol -l Ol 0]@ L l 1l 1J ll 1[@f i

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RE7C9T DAT E C

t>d 63 EVENT C ATE 6J 61 OCCAET % YSER EVENT DESCRLPTICN AND PROBABLE CONSECUENCES hencin-r 4

@ l'Aile in " ode S +he TMI-2 a-chitect E i sincie_ auxiliary transfer =er eteration within the nor-al ccerating rance

[

TT] 1v111 not provide sufficient voltare levels for operation of the L80 V totor c Because the unit has not been cperated l K jdurin; eriods of peak unit auxiliary demand.

tici for any l

t ;c mr level recuirine maxi-um unit curiliari :s, there was no poten E Lat l

E l a.-rre effect on the health and safety of the rublic.

1 5)

I& I l CO \\t P.

VA LV E 1

COMPONENT C001

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30 31 32 W.7ACHYENT NPRCM PRIVE COYP, CCYPCNENT MA%FACTUAER A '*Tr O1.

FUT' jai EFFECT SH UT0 0.*. N HOURS SV G r.'I TT E D FOR.'.t huS.

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CxusE OESCRtPTION AND CORHECTIVE ACTIONS hitect engineer afteq lojlCirgle trr.sformer oceraticn voltare studies cc-ducted by the arc t

tin ~

f voltage cetimizatien studies, chewed that vithin the nor".a'. crera iij lccenletin: the 7g j rang of the grid (232 to 23SK7) a cincie auxiliarv transforT:.cr can' t p

_a Ji"T] l *coltare levels to curecrt coeratien of the unit Engineerine Safety 1

'y, I t of rirt auxili ar'.c s.

(Continued)

C3 METHOD OF DISCOVE RY DES;mPTtC1 7

8 9 CISCOt E R V 5

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12 13 LOCATION of n;LE A32 ACTIY1TY CO'4 TENT AMOUNT CF ACTIVITY IA 8tEllA519 ** GELEASE 62 II$

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aTr/E TO ACCC:'?!JTf LER 78-35 On I'27 3,1978, the results of the single a= ciliary transformer voltage study were received frc= the Architect Engineer (Burns & Ree). The voltage values

1:ulated for the L8O V Motor Centrol Centers, for a nor=al voltage of the 230 E. gri:1 vere below the required h07 Y AC nece::::ary to assure ::are operation of the magnetic centroller.: and prevent centrol power fase blowing. These voltage values are ba: ed on having the -'vinu= unit auxiliaries in service during the cu ner =:nths, with all circulating vater pc=ps in service.

This ite vas determined to be a violation of Technical Specification 6.9.1.8.h, in that the Safety Evaluation Report states that each unit auxiliary transformer is sized to carry the unit full lead auxiliaries and the energized safety features a=ciliaries. Since the ESF bus povered frc= the inoperable transfor=er is designed to fast transfer to the re=aining transforner, the potential to disable both ESF trains due to centrol power fuse bleving exists.

Follow up stulies have verified that by aute=atically shedding selected Balance of Plant leads upon auxiliary transfo: :er failure, adequate voltage levels are available at the 480 V I'cter Centrol Centers throughout the nor=al operating range of the 230 rt g-id.

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Cause escriction and Corrective Actions In order to assure adequate voltage level, one of folicving corrective actions vill be taken: A) the unit vill not be operated above a power level ccepatibl to safe single transfer:er operaticn; 3) selective balance of plar.t load shedding vill be installed; c) er the automatic bus transfers to the other auxiliary trancfor=er for designated bus vill be disabled.

I P.

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j A:tichment #2 NYU h

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METROPOLITAN EDISON COMPANY s esmuc m m aoc w s

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4 PCST CFFICI Box 542 REAolNG.PENNSYt.VANI A 19603 TELEPHCNE 215 - 929-0E01 May 30, 1978 GqL 0961 Director, :Tuclear Reactor Regulatica Att :

Mr. S. A. Varga, Chief Light 'Jater Reactors Branch :fo. k U.S. Iluelear Regulatory Cc==issica

'Jashing ca, D. C.

20555

Dear Sir:

Three Mile Island :Iuclear Statien, Unit 2 (TMI-2)

Operating License ?Io. DPR-73 Docket :To. 50-320 In response to questions raised by Mr. Rarlay Silver of your staff, enclosed please find infor=ation concerning the potential probles as-scelated with the less of an auxiliary transfor=er at OfI-2.

Sincerely, Signed J. G. Herbeid J. G. Herbein Vice President-Generation JGH:[:cjg ec: Directc,r of ?Iuclear Reactor Regulatien Atta: Ha-ley Silver Light Wate: Pcactors Branch :To.

4, U. S. 'Juelear Regulatory Cc==ission

'Jachingten, D. C.

20555 Attachment a.

.4.

4.s G. T. Broughten C. W. Smyth

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v. s'~ i+~""*" e R. M. Kling2=sn J. R. Stai '-*

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Shav, Pitt=an, Potts i Trcvbridge File: 02.0016.C001.C001.02 13C0 "M" Street, :T.*J.

62.1000.77CS N - " *,g Washingten, D. C.

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g li=ited to the values =entioned above, the less of an auxiliary transfer =er, and subsequent transfer of lead to the re=aining trans-fer=er vculd result in voltage levels sufficient to ;ick up all safety-related cc=penents necessary to =itigate the censequences of a LCCA, and cc= ply with General Cesign Criteria 17 of 10 CFR 50 Appendix A.

The Eu.ms and Ece Voltage Program used in =aking these dete. '"ations is the same pregra= which was used for the OiI-2 Voltage Optimization Studies.

The accuracy of this program was verified thrcugh field

=easure=ents at that ti=e.

II.

Len: Ter= Corrective Action In order to operate safely throughout the normal grid range (232-238KV) a longter: correctie'n action cf selectively tripping plant leads upon the loss of any Auxiliary "'ransformer has been developed. A syste= of relays vill be installed which vill encure that whenever an Auxiliary Transfor=er becc=es de-energized, the following plant 1ccds vill be tripped:

A) 2 - Cirt11ating Water Pumps B) 1 - Ccndensate Ecoster Pu=p C) 1 - Heater Drain Pu=p Burns and Ree has perfor=ed an analysis (using the above -centioned voltage progra=) to show that tripping the above-centicned loads vill provide the folleving h80 USS bus voltages:

h80 V USS* Voltage (1 Auxiliary Transformer Operation)

Grid Voltare Ncr:21 LCCA (Prior to Lsst E5 Ccercnents Starting) Post LOCA 232 KV h26V 411V L0h V**

• 'This is the voltage level after all ES cc=penents have started. ko7V is needed for starting ec=ponents, however, ec=penents vill safely operate at a =uch lover voltage (368 volts).

As can be seen frc= this chart, the voltage available for starting the last safety-related ec=penents (kil V) exceeds th*e voltage required for starting those ec=ponents (h07 V).

Also, the voltage available after all safety-related ce=ponents are started (kok V) is far in excess of the voltage needed to keep th;se ec=ponents operating (368 V).

It is hoped that these long ter= corrective actions can be inplemented within the next six weeks.

T5% results of tripping the above =entioned loads uten the de-energi atien of an Auxiliary Transfor=er vill be an autenatic recuction of unit power to approxi=ately 50%.

(Sis vill be acec=plished autc=atically by the ICS syste= due to the trip cf the Ccndensate Ecoster Pu=p)

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CFT. 3 's". 22=:.S. ST. S.-_.4 Attach =ent #5 S.,.3 D.r.e., c_, v a..m..i As she 's c Figure 3.2-1, de offsi:a scurces of a d11a:7 pcvar for :he uni:

m are suppliad by do auxilia:y ::ansfor ers 2A and 23, which are ::=ec:ed :o 3us 4 and Sus 3, raspec.1vely, of :he 220 'ci subs:a:ica.

The 220 'c, sub-s:sti:n design 12:::pora:es a breakar-and-a-half scheme f:: high reliability.

Since ei-lar 3us 4 c: Sus 5 =ay be ce=ec:ed :o any =ans=1ssion line, at:her bus say be ccesidered a preferred scurca.

7chage is stepped deva :: 4150 a:d 6900 ve hs and delivered :o he cust:a dis u ibu:100 systa= th: ugh :: -

segrega:ed =ccal-enciesed bus duc:s and fur-der.h:: ugh =e:al-clad sain svi::hgea: 5:eakars.

2he 220 'ci subs:a.ics is cc=ected : the exis:ing Me=cpcli:a= Idisc: C =pany l

220 'ci rans=1ssics serverk by three circui:s, :vo circui:s going co :h :o Middle-

va Junc:100 cc a double circuit :cver. Middle::va Junctics, loca:ad 1.5 =iles fres ! area Mile Island, is a =ajor subs:2:10 in de Pe=sylvania-New Jersey-Maryland h:ar::=ec:10, virh 220 'ci = ass =1ssics line c:=e :1cus cor h to Hu=els::v, eas: :: Scud Rezding, and scu.h :o 3:n=e: 2sland, a 1500 My generati:g sea:10: cweed and opera:ad by Pe==sylva:12 ?:ver and ligh: Cc=pany.

An au::::assic:=e: :1e is:are:::ec:s -la 220 'ci substa:1c: vi:h de 500 kr substa:10, :o vcich de cc:pu: of Uni: 2's geners:c: is delivered and f:c:

welch lines ru: to Ecsessack, Peach So:::s and Ju=ia:2.

The output o f "D1I Cait l's genera::: is also delivered :o che 220 'ci subs:acicc.

51:1 ::ans=issics lines are ::ueed as sheva c yigure 3.2-2.

h:ere:::ac:10:s are shown c :he singla li:e diagra=, Figura S.2-3.

L ca:10 of da ac:ar7

ansfor=ers and reu:ing of the dis::ibu:1 duc:s :o the ossi:e buses are shows c Figura 3.2-4.

The sy=bols used c: -la figures presented in dis s

chap a are defined : Figure 3.2-5.

3.2.1.1 A=airsis of Ces12: Cri: aria 8.2.1.1.1 Cri:arie: 17 - Elec::i: ?cver Systens F.lacuic pcuer fr:s de ua s=1ssion se: c:k :: de c si:a elacci: distribu:10 systen is supplie by :vo physically indepe:de-- -' - ' s designed and loca:ad so as :o

'-d

' e :o de ex:en: prac:ical da likahheed of : heir si=characus failure = der opera:1:3 and postula:ad accides: and env.:: =a.21 c: r.1: ices.

Cua :f cui: is supplied fr:s Auziliary Tra:sf: =e: 2A c==ec:ad to 3us. Of de 230 'ci substa:1:, and the c:her circui: f::c A"rd=ry Transfor=er 23 c:enec:ed : 3cs S.

F.ach circui: sc:.:all7 supplias cue-hald of da unu d sry a:d safa:7 leads, h de even: of a 'f alkre of at:har ci:=1--

=ansf ar of de leads to de :=-m'-'

g scur:e is ac :=plished au::, a:1: ally by relay and breakar ac.1:0.

Re vai of the faulty circui: and =ansfer

the :=-ad

' g scur:e of offsi:e pcver vill occur vi:hin 6 cyclas fc:

sco : circui:s de:ac:ed *-

'e 220 'ci bus and fand 1::ui:s.

T e pr:':abili:7 of power f a"-= 4"e Oc fauhs in de natuc:k in:ar::=ac:icts is

-d-'

' ad by de folleving :C bill:7 c: sidera-ices:

a.

""he :vo 220 'ci Middle :v: June:10: Circui:s ara

• canad :: diffaren:

double circui: :: vers.

1. e d

.M.

g P - ~'o

?

~,

b.

ne lica :o Jacksca fc11cus an en:iraly dif feran: : u:a :han de li=es :: :iiddle::ve June:1:. ne lines ara in physical pr:xi=1:7 :o

^

each c:her in :he statica sv1::hyard. Never heless, :he sac =e::7 of the :: vers =nkas si=ul:2: ecus s::ue: ural d:= age unlikaly.

he envi-

an:al design of :he towers =akas d-

" 'dkal'/ da: duy :uld bc:h fail f::= a c==== a vi::::an:al cause.

An envir: =en:al effac: severa enough := cvartura cae : ver in:o de other would al::s: certainly have firs: :esul:ed i= less of offsi:a pewar.

c.

L e Middle::vn June:ica substa:ic is caly 1.3 =11es away, thus reducing line exposure.

d.

An au:o::ansfc=e: cia is p:cvided :o cie che 500 *ci subs:a:10, in:o which Cai: 2's generator discharges 1:s cu:pu:, and :he 230 'ci sub-statics f := vhich Uni: 2's auxiliaries ob ain : heir power.

Less of de ::.a vill co: shu: dev: :he uni:'s aux 111 arias.

e.

ne breakar-and-a-half switching arrange =ent is the 230 kv subs:a:1c includes :vo full capaci:y =ain buses. ?:1=ary and backup relayic.g has been p cvided for each circui: a10 g vi:h circui: breakar failure backup svi:ching. nese p:cvisicas pe=1: the fciloving:

1.

A y circui: can be swi:ched u= der sc:=al c: fault condi:1cas vid=u: less of exter:al pcuer sources.

2.

Any si:gle circuit breaker can be isola:ed f:: mai=:anance without 12:errupting :he pcuer c: procac:ica :: any circui:.

3.

Sher: circui: of a. single =ain bus will be iscla:ed vi:hcu:

in:errupting service :o any cutgoi:g line c: :o the plant for

=cre :han 6 cycles.

4.

Sher: ed--"'-

• allura of :he :1e breakar will esul: in the less of 1:s :vo adjacent circui:s us:11 1: is isola:ed by dise ::act switches.

5.

Shor: circui: failure of a bus side breakar will resul: in the loss of cae circui: and One auxiliary transfc:=ar us:11 1: is isola:ed by disconnect svitches.

6.

Circui: p:ctectic: vi.ll be insured f := fail =e to the primary protective relaying by backup relaying.

7.

Each "eaker has dual trip ecils, cne supplied f'-c= a pr - / and 0:e d

fre= a backup scurce. 3cth of these scurces "a

a'

• #cally independent.

Although these circuit ' are act physically separated, each ;cver s==ce has redundant $ sing.

f.

T: assient stability studies for the bulk ;cver trans=issica syste= have been perf' =ed as discussed in 3.2.2.

m

'Jith the above prctective features, the probability of less of Ore :. - cue scur e of 230 kv pcver fre= faults is icv.

In the " ' n 17 event of less of all of the 230 e

kv offsite pover, the er.gineered safety feature leads vill be supplied fr = cae er

=cre of the r-"d d g scur:es of cesite power as discussed in 3.3.1.

3 e.- -os 3,2 2 4.

Os A-w-tw) os-

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