ML20106F939

Forwards Addl Info Requested in Re Tech Spec Rev Concerning Protection of Cable for I2t Rating.Protection of Cable Integrity & I2t Rating Verified Through Demonstration of Breaker Function

ML20106F939
Person / Time
Site:	Summer
Issue date:	02/06/1985
From:	Dixon O SOUTH CAROLINA ELECTRIC & GAS CO.
To:	Harold Denton Office of Nuclear Reactor Regulation
References
NUDOCS 8502140157
Download: ML20106F939 (10)

Text

4

,M' SOUTH CAROLINA ELECTRIC & GAS COMPANY POST OFFeCE 764 COLuusiA south CAROUNA 29218 O. W. Druom. Jn.

uuc$*.In""o','Er"[o~.

February 6, 1985 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C.

20555

Subject:

Virgil C. Summer Nuclear Station Docket No. 50/395 Operating License No. NPF-12

-Request for Additional Information - Cable Separation

Dear Mr. - Denton:

In a. letter to you dated November 29, 1984, South Carolina Electric and Gas Company responded to a condition of the Included in Operating License on cable separation (Item 2.C.16).

this letter was-a request for Technical Specification revision.

In a.. letter from the Staff dated January 8,1985, additiongl information was requested on protection of the cable for I t rating.- The attached information is in' response _to that.

request.

If-you have any further questions, please' advise.

e tru

yours, O.

D

, Jr.

JAW /OWD/gj l

Attachment:

cc: T V. -~ C.

Summer' C. A. Price-T.

C. Nichols, Jr./O. W. Dixon,- Jr.

C.

L. Ligon (NSRC)

E.

H. Crews, Jr..

K. E. Nodland-E. C. Roberts R. A.

Stough

'W. A. Williams,.Jr.

G.

Perciva1 D. A '. Nauman C. W..Heh1-L J. P. O' Reilly J.

B.

Knotts, Jr.

Group Managers NPCF O. S.

Bradham File-b}U 1

n0(

8502140157 850206 PDR ADOCK 05000395 p.

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QUESTIONS 1.

Your letter of November 29, 1984 does not demonstrate that the associated cable protective device will cle r the imposed fault condition without exceeding the Igt rating of the cable (before the ignition temperature of the cable insulation is reached).

Therefore, provide for Staff review some typical protection device gurves for the subject circuits plotted against the I t curve of the cable;which it' protects.

~2.

'For all of the subject circuit cables protected by overcurrent protective devices,2are those cables protected equal to or better than their 1 t curves?

l 2

-=

l-Attachment Page 1 of 9

RESPONSE

The. Virgil C.

Summer Nuclear Station cable sizing is designed in accordance with industry standards, and the circuit breakers are also designed and sized in accordance with industry standards.

LThe circuit breaker's function is to protect the circuit, i.e.,

cable and equipment, in the event of a malfunction of the cable i

or equipment.

r The. Virgil C.

Summer Nuclear Station cable sizing is governed by the Project Design Criteria Manual, Chapter 4, section 4.7.

This design criteria was developed by Gilbert / Commonwealth, Inc.

for F

use in designing Virgil C. Summer Nuclear Station.

The criteria is based on cable industry standards.

A conservative margin is I;

factored into the plant design via this design criteria.

The applicable section is attached as Reference 94.

i j'

The size of a given cable for a load is also increased based on a derating_ factor if installed in cable trays.

Thisderatingadds to the conservatism of cable selection and increases the I t capability'of a given cable.

n l.

. Examples of typical protection device curves plotted against the 2

I t curve of the cable it protects are attached:

4 1.

A typical 600V air circuit breaker for the Virgil C. Summer Station'is a Brown Boveri (ITE) 600 Ampere, K-600, circuit breaker.

From Reference 64, table 4.18, the maximum allowable ampacity for 750 MCM copper cable is 492 amperes, random lay.-

Therefore the long-time setting on the circuit 4

-breaker would be 0.8 or 480 Amperes.

4

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'From-Reference $1, the short circuit allowable amperes for various times for 750 'MCM cable were determined.

Reference il is an Allowable Short Circuit Current table taken from a cable design handbook. ' These values of allowable-short circuit amperes'forfthe cable wereithen plotted on the 1 Time-Current Characteristics ' curves for the breaker; Reference-92. -From.thgsplot;it-isevidentthat-the: breaker

will. trip before-the I t'of-the cable-is reached.

E 2.

A typical 600V Molded case circuit breaker for the Virgil C.

Summer Station is aESquare'D 100~ Ampere, FA! circuit breaker._

From-Reference 94,-table 4.12,.the' maximum allowable'ampacity-E l'

.for 1/0 copper. cable is'130. Amperes. lTherefore'the 100

. Ampere breaker would protect the cable..

If the' cable.was:

z routed through a random layfcableLtray,Ja.derating factor

would be; applied,-and thelampacity'would be taken from

' Reference?t4, tible 4.18.

The'ampacity would then be reduced to 86 amperes and an ' 80- ampere ~ breaker would be used' to protect the.' cable.

s Attachment Page :2fof 9 '

'E s

4 4

3

__ - - -..-.._,._.- _ _ _. _., _. _. _ _.... _ -. _,, _ _.,.. _.~... _._.

f RESPONSE ( cont' d )

'From Reference fl, the short circuit allowable amperes for various; times for 1/0 cable were determined.

These values of' allowable _short circuittamperes for the cable were then 1

plotted on the Characteristic Tripping Curve for the FA evidentthat-theibreakerwilltripbeforetheIgotitis 100_ Ampere, breaker; Reference #3.

From this p t of the cable is' reached.

n Circuits for the Virgil C. - Summer Nuclear Station are designed in accordance_with the Project Design Criteria Manual which factors in a conservative margin to assure that the circuit breakers function ^to protect cable and equipment.

The cable design criteria used for sizgng the cable feeds from a breaker gives consideration to the I t capability of the breaker to protect the-cable.. Therefore it can be concluded that if the nction then the integrity of breakers are demonstrated to fgt of the cable is not the cable is' insured and the I

. exceeded.

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' Attachment Page 3 of 9 4

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Okonite Cables Section 4 REFEREMCE #1 O

i Short Circuit Currents 4

i; Allowable short circuit currents for msulated copper conductors

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conductor size must be large enough 3

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The chart at right shows the maxi-a' BEEEif mum currents to which various size

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Attachment Page 7 of 9 R

4 4.7 CABLE RATING CRITERIA 3

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Motor feeders, power panel feeds, and small lighting and 3=

receptacle panel transformer feeds will be sized for 125% of full d

load current. Large power transformer feeders will be sized for 140% of full load current at maximum rating. Motor control center c-feeders will be sized for 140% of the calculated normal 2

diversified load current, and feeders to resistive loads will be sized'on the basis of 110% of rated current at rated voltage.

(5 E

In sniecting IPCEA ampacity tables, a load factor of 100% shall be d

assumed.-

Ampacities of 7.2 kV power cables will be in accordance with IPCEA

{-

in air ratings derated by a factor of 0.7.0 in 400 C areas and 0.63 S

in 500 C areas.

=m Ampacities of 480 volt cables or large DC cables in single layer

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power trays will be in accordance with IPCEA in air ratings and i

derated by a factor of 0.70 in 400 C areas and 0.63 in 500 C

?

areas.

5 Ampacities of 480 volt cables or DC cables in a random lay power 4

tray shall be in accordance with IPCEA - NEMA Standard Pub.

P-54-440. The derating factors'for 3-inch depth shall be used.

Ampacities of 480 volt cables or DC cables'f10 and smaller, when run in the control tray, will be in accordance with the.IPCEA in y

air ratings derated'by a factor of 0.50.

2 Control cables and instrument cables will have no ampacity 5

derating factors applied.

_1_

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All smpacities are on the basis of 900 C tables at 400 C ambient in all interior areas except containment. Containment or ESF

_9 motors in areas. requiring forced ventilation of ehe motor shall be g

q on the basis of 500 C ambient.

A Pressurizer heater' cables will be sized by special ratings.

j i

The Reactor Building recirculation fan motor power cables require 3

special consideration,'since'these motors must operate'in the post-accident containment. environment. These cables will be sized j

3 to carry the required current, during the post-accident 8

temperature and pressure transient,'without exceeding the d

. recommended emergency operating temperature rating for the cable and continue to operate for_a minimum time of six months 5

post-accident.

Ampacities for 7.2 kV and 480 volt three conductor cables iti.

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conduit wrapped in Kaowool at 400 C ambient temperature are j.

calculated to ensure that the maximum copper surface temperature y

"3 of 900 C is not exceeded.

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4-33

-Attachment Page 8 of 9

'\\

.Raference 4 Paga 2 of 3l 4.18_

c480 V 39 PWR. CABLE RANDOM LAY KVA vs CABLE SIZE - 400 C AMBIENT (FOR NON-MOTOR LOADS)

OVERLOAD FACTORS MAXIMUM' CURRENT FOR MAXIMUM KVA FOR Cond.-Size.Ampacity 110% overload 1251 Overload 140% overload 110% overload.1251 Overload 140% overload 10 AWG 12 10.9 9.6 8.55 8.7 7.6 6.8 8

17.

15.4-13.6'

'12.14 12.2 10.8 9.6 6

28 25.4 22.4 20.00 20.2 17.8 15.9 41 39 35.4

-31.2 27.86 28.2 24.8 22.2 2

55 50.0 44.0 39.29 39.8 35.0 31.3 1

72' 65.5 57.5

.51.43 52.1 45.8 40.9 1/0 86~

78.0 68.8 61.43 62.1_

54.8 48.9 103 93.5

.82.5 73.57 74.5-

~65.7 58.6 l 2/0 3/0 124 112.0 99.0 88.57 89.2 78.8 70.5 S.

4/0 156.

'142.0 124.0 111'.43 113.1 98.8' 88.7 250 MCM 190

.172.0 152.0 135.7 137.0 121.0 108.1 350 MCM 250 226.0

-200.0 178.57 180.0 159.3 142.3 500 MCM 338 306.0 270.0 241.43 243.8-215.1 192.3 9

750 MCM 492 445.0 393.0 351.43 354.5 313.1 279.9

+

Attachment Page 9 of 9 R2fercnce 4' Pcgn 3 of 3 4.12 277 V 19 PWR. CABLE SINGLE LAY' KVA vs CABLE SIZE - 400 C AMBIENT (FOR NON-MOTOR LOADS)

OVERLOAD FACTORS l

MAXIMUM'KVA FOR MAXIMUM CURRENT FOR Cond. Size Ampacity 110% Overload 125% Overload 140% overload 110% overload 125% overload 140% overload 10 AWG 28 25.4 22.4 20.0 7.0 6.2 5.54 8

41 37.2 32.8 29.3 10.3 9.1 8.12 6

55 50.0 44.0 39.3 13.8 12.2 10.89 4

72 65.4 57.6 51.4 18.1 15.9-14.24 2

96 87.2 76.8 68.5 24.1 21.2 18.97 1

112 101.8 89.6 80.0 28.2 24.8 22.16 I i 1/0 130 118.2 104.0 92.86 32.7-28.8 25.72 2/0 150 136.3

'120.0 107.1 37.7 33.2 29.67 53/0 174 158.2 139.2 124.3 43.8

'~ 38.5 34.43 g

,0 4/0 200 181.8 160.0 142.86 50.36 44.3 39.57 e-250 MCM 224' 203.6-179.2 160.0 56.4 49.64 44.32 l

350 275 250.0 220.0 196.43 69.25 61.0 54.41 500 340 309.0 272.0 242.86 85.59 75.34 67.27 750 430 391.0 344.0 307.14 108.31 95.29 85.08 9

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