ML19225A805

Submits Addl Info Re Degraded Grid Voltage,In Response to NRC 790620 Request.Thirteen Oversized Drawings Available in Central Files

ML19225A805
Person / Time
Site:	Arkansas Nuclear
Issue date:	07/12/1979
From:	Trimble D ARKANSAS POWER & LIGHT CO.
To:	Reid R Office of Nuclear Reactor Regulation
References
1-079-4, 1-79-4, NUDOCS 7907200272
Download: ML19225A805 (29)

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4 r~ y g ARK ANSAS POWER S LIGHT COMPANY POST OFFG BOX 551 UTTLE ROCK. ARGNSAS 72203 (50H 371-4000 July 12, 1979 l-079-4 Director of Nuclear Reactor Regula tion ATI'i: Mr. Robert W. Reid, Chief Operating Reactors Branch #4 U. S. Naclear Regulatory Ccmnission Washington, D. C. 20555 Subject Arkansas Naclear Che-Uni t 1 Ibcke t No . 50-313 License No. DFR-51 Degraded G-id VoItage Request for Addi tional Ln f onr.a t i on (File: 1510)

Gen t i cron :

In response to your le t ter of June 20, 1979, the following is provided.

Iten 1.

Tne proocsed second level protection includes two-out-of-tau coincidence to cause protective action. D2 scribe the feature (s) of the design unich wi l l pe rmi t aut cma t i c prot ec t ive ac t ion when one o f the two channel s i s out of service (for calibration, repair, etc. ) .

Resoons e :

Tlw auxiliary power systen has two load groups (Red and Green) . Each load group is provided with two undervoltage relays (total of 4) . 'Ihe undervol tage protect ive action of the two load groups is independent. 'Ihe protection action within a group is initiated when both relays in that group operate (two out of two).

If one of the channels is out of service, the protection actuation systen for the other channel being independ is still functional. If one of the two rel.,ys in one channel is out of service for repair, maintenance or calibration, then two conditions will arise.

a. Relay is stilI counted and undergoing testing. The actuation systen will automatically revert to one out of one instead of two out of two relay logic.

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366 a4 VEVDE A M:001 '. SOUT H LTiLITE S Dvs TE Y

1-079-4 Mr. R. W. Reid July 12,1979

b. Relay is disnuunted fren the swi tchgear, wiring is rumved.

Administrative controls will be icposed to ensure the wiring continuity of the other relay. 'Ihe protection actuation sys t en wi l I be one out of one.

I t en 2.

Describe the design provision to autanatically reins tate the degraded voltage protection systen (both levels of protection) when the supply breaker fran onsite sourc^ is oper ' and, conversely, blocking the under-voltage protection when the onsi te source is supplying power to ESF buses.

Response

The design of the U/V protective systen is such that it operates only when the of f-site breaker is closed. The protective action is blocked when t he on-s i t e p"xe r br eake r i s c l o s ed anci o f f-s i t e br eake r i s open i.e., diesel generator is the only source of power to the ESF buses. 'Ihe protective action is autoratically reinstated upon closure of the of f-site breaker.

I t en 3.

Describe the features of the under-vol tage protect ion systen that facil-itate periodic testing.

Re spons e :

The 4160 Vol t undervol tage relays (two in parallel) are equipped wi th test plugs. Periodic testing when perfomed on one relay will be done by remving the plugs, and inserthg test plugs. Operation of that relay in that nude will not af fect the p.otec t ion systen. The protection actu-a t ion sys ten wi l l s t il l oc operational wi th the other relay in service reverting to one out of one instead of a one out of two logic.

The 480 Vol t undervoltage relays are eqaipped wi th a test in service pushb ut ton. Actuation of the pushbutton will exercise the solid state circui try, and close the relay contact. The protect ive act ion will not be executed when testing one relay at a tinr.

I t en 4.

a. Describe the testing to be perfonned on the under-voltage protect ion sys t en.

b. Describe hox the testing progran wil 1 demns trate that , when the grid is at the de fined "mininun-nomal " condi t ion, no unacceptable voltage is applied to ESF equipmnt. (If actual 366 dif$5 25s

1-079-4 Mr. R. W. Reid July 12, 1979 test cannot fully sinulate such a grid condition, sufficient tests should be conducted to facili tate extrapolation of the m2asured data wi th a high confidence level).

c. D scribe hox the testing progran wil1 demnstrate that, under the defined "minimin .onml" supply condi tion, no unacceptable electric power will be applied to ESF equiprent during the starting of large non-Class IE nutors.

Response

A. Every refue.ing outage two tests will be performed.

1. Calibration check to ensure proper set point.

2. Teut trip check to ensure control wiring and integrity of the protective actuation systen.

o. Tne undervoltage relays are alw,ys connected to the source and continuously nunitoring the voltage. When voltage is belox set point the relay dropout and protective action is initiated.

Eis dmunstrates t'. tat the ESF buses will not see lox v Tes.

C. Le analyt ical resul. s indi cate that vol tage dips rmy c' on the 480 Volt systen during starting of the reactor cooaa punp notor, under certain station loading configuration. The volt-age dip is belax the set point of 92% of 460 and exceeds the 8 second time delay. To prevent unwarranted spurious trips, the protective actuation systen is blocked during the acceleration pe ri od o f RQ , and au t ana t i c al l y re i ns ta t ed a f t er twen ty se-conds.

I t em 5.

The proposed under-voltage protection includes transfonners tap changes.

Provide the analysis that shoxs that, under high-normal conditions of grid vol tage and no-load condi tions, the vol t ge s appl i ed t o ESF equ ip-nunt will not exceed acceptable values.

Respons e :

The traxinun vol t age expe c t ed on the sys t en i s 1. 0 5 pe r uni t . Trans fonner taps were selected such that, under no load condition, and nnxinun ex-pected systen voltage, no significant overexci tation on rrotors will occur. Cmputer cases V-2A and V-3A (At tachnant 1) indicate the results.

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1-079-4 f.ir. R. W. Reid July 12, 1979 I t mi 6. 9 The proposed ur!dcr-voltage protection nudi fication includes a bypass of the second level protection durinsz the starting of large, non-Class IE rrotors. Provide the schenatic diagrans involved in this aspect of the proposed rrodi fication. Discuss hou this bypass satisfies IEEE-279, with carticular consideration to the f act that the bypass originates in non-lE equiprent and operates in both divisions of the Cless IE electric power systen.

Response

Drawings E-196 Sheet 1 Rev. 12-1 and E-99 Sheet 1 Rev. 8-1 (attached) covers the bypass of the second level protecti-a during large rrotor startingu.

a. Each reactor coolant pmp, 6.9kv swi tchgear , wi 11 be pro-vided wi th an of f-delay t itrer. Each of the two contacts of t hi s t ime r ( f o r each reac t or cool an t puap) wi l l be connec t ed independently in separate scheres and will operate individual class IE relays trounted on redundant class IE 4.16kv swi tch-gear. All the wiring for the two control schenus will be routed in separate race.nys (Note 1 on schene E-99 sheet 1). Relays nounted in class lE 4.16kv switchgears shall provide a buf fer to separate the two class lE load groups fran the non-class IE controls. The contacts of these buffer relays are connected in their respective load group protection schenes and are wired as class IE devices.

Itan 7.

For each Section of iEEE 279, describe hou the proposed under-voltage protection nodification cmplies with the criteria.

Response

The response to this i ten is be" , developed at this time and should be forwarded to you by August 3, 1979.

It en 8.

The proposed under-voltage protection includes shedding of non-essential loads.

a. hhat is the rmxinum load (MVA1 that nny be transferred to ST-1/ST-2 (worse case)?

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1-079-4 Mr. R. W. Reid July 12, 1979

b. Identify specifically wbich loads nust be shed.

c. Provide appropriate electrical diagrans which portray this shedding.

Response

The load shedding of non-essential loads is proposed only when the station auxiliaries are supplied power fran start-up transfornur No. 2 (#ST2). The load shedding is not a function of voltage magnitude but rather a line up.

a. The calculated nnxinun load (per the couputer load flow study) that can be fast transferred to ST-1 is of the order of 41 hWA. This does not include the ESF load which af ter transfer shall be sequenced in case of an ESF signal .

Tne calculated nnxinun load that can be transferred to ST-2 is of the order of 30 hUA which includes the ESF as wel 1 as the non-ESF ioacs.

b. then the source of power supply to station auxiliaries i s ST- 2, the following loads are proposed to be shed:

i. Two reactor coolant punps tripped (two running) ii. Three circula ting wa ter pumps tripped (one running) iii . Twa condensate tripped (one running) iv. Two chiller pumps tripped (none running)

There is not load shedding when the source of supply is ST- 1.

c. The following drawings show the load shedding (attached):

E-I l 8 Rev. 0-1, E-306 Sheet 2 Rev. 2-1 Sheet 3 Rev. 2-1, E-271 Sheet 1 Rev. 11-2 Sheet 2 Rev. Il-2 Sheet 3 Rev.

0-1, E-372 Sheet 1 Rev. 8-2, E-196 Rev. 12-1, E-92 Rev.

12- 1, E-89 Rev. 13-1 I t un 9.

The ANO-1 analysis assumed that protective action would be executed at (or above) the calculated value of 92% (nutor-base) voltage.

Indi ca te : (a) naninal value of this setpoint, (b) the al lowance (above 92%) used to accamodate all inaccuracies, and (c) allowance (abnve 92%) used to accamudate drif ts. Describe the basis for detennining these allowances. Describe the bases for detennining the 366 258

1-079-4 Mr. R. W. Reid July 12,1979 nominal setpoint which provides maxinun protection consis tent with miniaun spurious shedding fann the perf erred power source (i .e. ,

electric grid).

Respons e :

a. The naninal value of the 92% under voltage relay is 105.8 volts drop-outwhichab04 0 volt systen level correspon& to 423.2 volts (105.8 x h and on a notor base of 4600 is 92%. The basis of selection of 92% of 460 as a nominal set point NBR s tandards al lows 90% vol tage on tro tor tenninal plus an added 2% voltage d op between autor tenninal and load center buss uns considered in the se!cetion of set point (90% + 2% = 92%

of 460).

b. The elays were f actory set to drop out at 10 5. 8 vol t s (92%

of 460 + 4 pt ratio). No inaccuracies are accounted for.

c. As these relays are not ins tal led at A'D-1 as w t , the necessi ty for determining setpoint s (and corresponding inaccurac:'s) has not risen. lbweve r , in response to your question and in preparation of installation, set-points are being developed and will be forwarded to you as soon as they are available.

I t en 10.

The AP&L submi t tal da ted Augus t 23. 1978 indicated that the setpoint for the under-frequency trip would be 59.9Hz. We understand this value is erroneous. Please indicate the correct value for this setpoint.

Response

The 59.9 Hz value is indeed incorrect due to a typographical error.

The correct value is 59.5 Hz.

I t en 11.

We understand that AP&L proposes to use interposing relays to inprove control circuitry voltage situation. Provide typical diagrans showing these circuit changes and state the criteria and design voltage limits that will be inposed.

Response

The diagram E-84 sheet 5 shows the typical changes proposed to add interposing relays. The criteria and design voltage limits are listed below.

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1-079-4 Mr. R. W. Reid July 12,1979

a. Starter minirnm pick-up voltage 80% of 115% (obtained f rau Motor Control Centers supplier, Allis-Chairmrs),

b. Control transfonmr voltage applied to prirmry 90% o f 46(V.

c. Maximum control wire length were calculated for various sizes of starters so that the voltage at the starter tenninals does not f al I below the minimmi requi red under i ten 11.a) . The fomula used for voltage drop calculations are as follows:

% Regulation = Vg - V X 100 = (P r) + (qx) (Px - gr) Ioad Current Vgg 200 J X Rated Current there:

Vg = No lot.a vol tage on secondary of control transfer Vg = Ioad voltage on secondary, given load current.

Yh ted = 115V AC. , Cont rol t rans fome r 0 = Ioas power angle (starter inrush)

P = Load power factor - Cos 0 q = Sin 0 x = % reactance control t rans fonne r r = % Resistance control n ans fomer Imad Current = Starter Inrush Current Rated Current = Control Transfer Rated Current The data for the starters and control transfonner is supplied by the Vendor.

Wi th regard to your request for prcposed tcc.hnical speci fications, our letter of August 23, 1978, ccnmitted to provide proposed Technical Speci fications following NRC approval of our proposed rmdi fications.

As the proposed rmdifications have not been approved by NRC and have been the subj ect of extensive review and question, we are uncertain, at this t an, as to the status and likelihood of NRC approval of the proposed rrodi fications. Based on this we do not believe i t pradent or in t' e interest of expeditiou:ly resolving this issue to propose Techni-ca' Jpeci fications based on speculations wi th regard to the outcone of 366 260

1-079-4 Mr. R. W. Reid July 12,1979 NRC's review. Ilowever, repeatine our previous canni trrent, v.c will sub-mi t proposed Technical Specificulons irmediately upon your approval of '

our proposed rmdi fications.

We hope you are synpathetic wi th our above concerns and recognize that our ef forts are those which we belie m will resolve this issue in the trost rapid and ef fective rmnner possible.

~

Very truly yours, boar &O(.h David C. Trimble Manager, Licensing DCr/JTE/ex o,1 366 20