ML20079A918

Discusses Current Transformer Cracking Problem at Facility. Proprietary Current Transformer Data Sheet Encl.Encl Withheld

ML20079A918
Person / Time
Site:	Brunswick
Issue date:	05/14/1991
From:	Egli A PIEDMONT DIELECTRICS CORP.
To:	Naidu K NRC
Shared Package
ML19302E604	List: ML20079A918
References
REF-QA-99901234 NUDOCS 9106100137
Download: ML20079A918 (9)

Text

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.1) oc.w. ET 99900 835 pieamoni mieioctrics Route 2 Hwy 221 IporOtiOI~1 Totephone (803) 4N-8141 PO Dom 729 Telecopier (803) 4N 8141 Wcuiruff, SC 2938B E ntenuon 20 May 14, 1991 Mr. Kamal Naidu Mailstop 9D4 US Nuclear Regulatory Commission Washington, D.C.

20555

Subject:

Current Transformer Cracking Problem CP&L Brunswick Power Generation Plant

Dear Mr. Naidu:

Ref erence is made t o this morning's telephone conversation regarding your investigation into subject current transformer.

Per your reluest I am sending you the following:

Test reports HR-200%9 and MR-2009A Sketch SK-9117, showing the design concept in general PDC catalog, page 1, Section 2.7.2 with C.T.

outline ANSI /IEEE Std. C57.13-1978, page 23, Table 11 wit'n burdens Metering data sheet TD-6041, Rev. 7 I hope this will suffice.

If you have additional questions, please contact Bill Johnson since I am going to be away from the office from May 15 to May 30.

Sincerely,

h. W.

M Albert W.

Egli Vice President Engineering I 1 c.c.

Eill Johnson ABB Sanford

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l ENGINEERING DEPARTMENT TEST REPORT Date:

Apri1 12, 1991 Report No.: MR-/009

Subject:

MC9 21 Current Tranuformer: ( comm i ac i oned 1 9 '/. ).

Cracking of E-1 putting compound while in nervice at Carolina Power & l.ight Co.'s Brunswick Nuclear Power Generation Plant.

Object:

f;etermination of 60 Hz Withstand capability on almilar current transformer wi t h exponed conduct ive paint ground layer ( Simulat ion of crack i n pot t ing compound )

Gackground:

Subject transformern were vioually int.pected in Janu-ary 1991.

( 23 ) unito of various ratins were found with hairline cracks i n t he pot l ' no compound.

Tu accew t he situat ion het ter. Al Egli vioited CP&L 's Brunswick plant on April 11, 1991.

These transformers are part of the Emergency Power Supply System.

The following cells were inspected:

" COMP. AK 5, RX CORE SPRAY" - Found 200/5 A C.T.

cracked on A-phase

( f eeder si de )

" COMP, AK 4, RHR SERV. WATER PUMP 20" - Found ( 2 )

150/5 A C.T.u cracked on A-

& C~ phase.

"AF/ CONV SEHV W1R PUMP IB" - Found 100/5 A C.T.n cracked on A-phase and "new" also on D-phace.

The ( 5 ) C.T.s inspected showed the same crack pattern as chuwn in Figure 1.

The question arose what the implications were regarding the uafety of the plant if thene units could not be exchanged right away.

It was point ed out Lhat the function of the C.T. was not im-paired.

However, the Impulse Withutand level had to be quenttoned.

It was agreed that testn would be run in PDC's laboratory on a similar unit with a nimulated crack.

Test Set-up:

An MCG-25 current tranalarmer. P/N 401572-KS, 200/5 A

( ident ical in design to 401153-15, except for corona rating), was cut into the pottinq compound aurface down to the conductive paint ground layer, thuc expouing it to the atmosphere, thereby simulating the crack in subject current tranuformers.

The tranu-former was tected by itnelf. The boot at the upper conductor end was om i t. t ed.

1he conductor was ener-gized with 60 Hz voltage while the secondary winding and ground chield Were grounded.

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Test Resulto The t ransf o; mer withotond 40 kV rms for ( 1 ) minut e and flashed over at 42 kV.

Thiu in t he equivalent of i

I 56 kV creut withotand and 59 kV creat flauhover.

The " neck" of t hin t ranuformer extended 4.5" above the l

poured pot t ing compound sur f ace.

The ntrike dintance in ai r eau apin ox. 5.25".

A aimilar t ranu fortner. "nec k e x t endi ng onl y 1.62" above the notting compound surface, with a utrike dictance <,, approx. 2.25*,

flashed over at 32 kV rmo, I

the e4

'a l e at to 4b kV creut.

lest conditions were Temperature 20 C l

metric preut.ure 29.71" i

7 ativo humidity 26%

Conclusionat Daned on 60 H7 performance of t he t ransformer with i

the 4.b" high " neck" the c'ack in the pottinu con poend does not seem to ciur.ificant1y reduce the uit withutand capabj3ity below 60 kV.

Recommendation

• To fully comply'Witb nNSI Standarda C57.13-1970, the current transformero need to be replaced.

As a temporary meanure, to counter-act Ihe defIclency caut,ed by the crack. it is suouer.ted that the boot coverino t he upper connect ion bet ween the C.T. bar and the inuulated bun, be taped over cecure1y ta prevent any poualbility of a.flanhover to at ti ke between t he C.T.

" neck and the boot uleeve !.D.

f Prepared by:

Albert W.

Egli i

Dictribution:

Ray Drew CP&L John O'Connor CPhL

. Will 4 6:n Johnson AB9 Sanford l'

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PIEDMONT DIELECTRIl;S CORPORATION ENGINEERING DEPARTMENT TEST REPORT patc:

Apri1 17, 1991 Report No.* MR-?OO9A Subject MC 3-- 21 Cur r ent Tranuformer, p/N 401153-15, SrR. 99450.

Unit was returned from Carolina Power 1. Light Co.'o Drunswick Nuclear Power Generation Plant. Droblem: C-1 potting compound was found cracked when pulled from utock.

Objects Determination whether crack has a detrimental etfect on the performance of subject current transformer.

Dackground:

Reference is made to Test Report MR-2009.

To be able to be more cpecific under "4ecommendationo" in that report, t his t ranuformer was shipped to PDC by over-night expreno.

It arrived at the start of t he day shift on April 17, 1991, it wau cvDjected to all routine O.C.

teotu pluu come speciale.

Daued on the Serial number af subJeot C T. and the oldent ( 1975 ) records f ound i n PDC 's ?.C. records, it muot have been built prior to 1975.

Test Resultat 1.

Corona Inception / Extinction voltage 12.0 / 9.9 kV Diccharuu reagnitude at CIV/CEV:

15 / C pC 2.

60 Hz Withstand 06 kV for 1 minutes o.k.

3.

60 Hz Flachover:

61 kV r.m.n. several times. Flashover did not go t hrough crack.

4.

400 Hz Anplied Voltage:

200 V, 0.355 A, 10 seconds: o.k.

5.

Metering Accuracy:

Durden:

Sec. Current:

Ratto Correct-Phace Accuracy lon Factor:

Angle:

Class:

O 0.1 0.5 A 1.0028

+11.G' O.29%

5.0 A 1.0013 45.4' O.13%

DO5 0.5 A 1.0064 420.1' O.64%

5.0 A 1.0041

+10.3' O.41%

G 1.O O.5 A 1.0164

+46' 1.64%

5.0 A 1.0105 414.4*

1.05%

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Phynical:

Shore hardemuu o f Er l :

D-3S

( norma l when new: 4 7 -413 )

Discunofon:

Al1 electrical test recultn are r,til1 fine and were not affected by 1he crack at al1.

Since the cutona level to good enough for a 15 kV syntem and the 60 lu flachovern went f rom t he primary conduct or to thu secondary terminals, it can he concluded that the crack ic only superficial at thin time.

The E-1 putting compound i t. nofter than it should be Thio lo conulatent wit h t he " reversion problem

• identifled a fiw yearo ago.

For an aralynio of the crack fntmation, cee Tect Report MR POD!?D.

==

Conclusions:==

Subject current tranaformer io elect r ical1y cound at thin time.

The nuriace erack had no effect on the perIormance.

Ihe potting compound has softened bct in atilI conoidered acceptable.

Recommendation:

Since the results of subject current trancformer do not nececcarily r epr et.e n t all cracked transformero at CPAL Co's 13runuwick Nuclear Power Plant, it is otill recommended that they be replaced within 18 months.

To ca f eguard against any eventualltiec, taping of the boot io st ilI recommended.

Prepared by:

Albert W.

Egli Dintyibutlon:

Ray Drew CP&L John O'Connor CP&L William Johncon ADB Sanford i

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PlOdmOfit Swtion 212 lOIOCiflCS Page1 Ofpdf0 tion May 1,1989 Instrument Curfont Transformers 9

TYPE MCS 21 outhne D*g 401149 1

Type Construction: Der secondary ferrninetion Date:

156 V. Incioor

. Application: Metering & Relay intert: 10 32 X 7/I6 25'00 Hr. 95AV Bil Mounting: Jump or Riter Out Hecommended Terminal Screw:

Thermal Rating Factor: 1 33

12) 10 32 a 1/2" 7.5,15KV/1200 & 2000A Switchgear H,pon soc 6,t Head Cap Screw Appromimate Weight: 4 2 lbs.

mth Flat & Lock Wether. Ced, mum Plated (Not included) ow

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Relaying 0,,e n e,e n Rating Numter 80.1 l

B0.2 ]

B0.5 l

B 1.0 l

82.0 Accuracy "X"

50'5 401153 71 12 24 CN 41B75 75'5 401153 T2 06 12 24 48 C20 4 1875 100'$

401153.T3 06 06 12 24 48 C50 4 1875 1'M 401153 T4 03 03 06 12 24 C*iG 4 1875 l

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6 XC5 401153.T6 03 03 03 06 1.2 C',0 1 875 435 401 t L3.T 7 03 0?

03 03 06 C1N 1875 t

I A'! dimem.ons see ikoen.n enches I

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Ilut in the core of the trannh'iner does br t haves on a rated mondary (arrent of Ine A tlu I A il 20 I

-s bi

'ati apprecishlc tiftet on the ratio ur ration within times rated) and standard burdens. The soitve the lunits of c urrin; and burden outlined in 6.4.1 ratings and their amiated burdens are as fol-12h no that the ratio ran be calculated in at-lows:

cordante with M.I.10.

blauilh ation tovers current transforsnern in which the leakar.c flut In the core of the tran1

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'forrnet has An lippre(lable efft&t on the ratio

%dtere listde 11 within the lignits hpecilled in 6.4.1 (2).

An apprechble effect in defined an a 1 percent f,$

h differente between the actual ratio correction and 50 HD5 i

the ratio correction (elculated in accordance with IN UI M,1,10.

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600 11 H l2h $Wont$Uty Trftninal Vollage Nulstry Thls la the voltage the transforrn*r will dehver to a if a current transforrner is rattd at othtr than blandard burden at 20 tirnen rated secondary cut.

5 A, appropriate voltage ratiny values inny he de-rent without esteeding 10 percent ratio correc.

rived by rouluplying the 'ai ' nd soltare rating I

tion l'urtherinore, the ratio correction triukt be values by 5/(arnper s rCinri for such trans.

litnited m 10 percent at any current froiti 1 to 20 forrners, the hurde.. us h

'i',ed as in Table 11 tirnes rated secondary current at the Flandard and the secondary terrnb.... voltage raung will be hurden or n iy lower Standard burden used for the resulting value at 20 tirnes rated mondary becondary terminal voltage ratings in the follow.

current. For example,if the rated secondary tur.

7 I ing table. l'or etAidplasschly.acairacy clars Citu rent is 1 A. the butden corresponding to 102.0 will roeans that the ratio can be calculnted and that he 2.0 tirnes 25, or 50 !!(at 0.5 power fat tor); and the ratio correction t.ill not exceed 10 perccnt at the corresponding secondary terrninal voltage rat-any current from I to 20 tirnes rated secondary ing will be 50 times 20 times 1 1000 Y.

current with a standardi,0 0 burden (1.0 H tirnes G. l.2 HijiyMf &cAn<for,e or Mults. Ratio ('ur.'

fenr;Tran.6/oinWl'lieJ eld.Waccuracy clk" ap '

5 A times 20 times rated secondary current equahi 4

100 Y).

htINi:Lhly;1 <U t lis tdli tu i nd in gi: tmless. ot h e r w i<d Secondary terminal voltage ratings are based CiWeiRal;lif transformers have C clanific ation on Tahle 11 Standard llurdens for Current Trannfortners with 5 A Secondaries'

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Hurden l{esistance Inductance Imicience Amperes P o er j

llesignetnint (u) gle (u)

(at 5 A)

}sctor Metering Iturdens H 0.1 0 03 0 110 01 26 09 11-0 2 0 18 0 732 02 SO 09 H.0.5 0 45 O Sk0 05 12 5 09 il 0.9 0 81 1.04 09 22.5 09 918 1.02 7.On jk 4s u o9 h

l{elayir,r liardens 14 1 05 2 l1 1.0 i$

o5 h2 1.0 46 20 50 o5 11 4 20 0.C& 9.2.

4o 100 o6 li R 40 1M 4 l' 0 MI O5

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• !f a turn nt transf.itn.er is rated et other than 6 A, olon4 tiurderm f.r +n da noon ml t v u m m in b I I de rned by mulopising the tr,mn(c and mduc tanic of the table b.i,', amorn t rioW O c \\ A at ev.-d c ur rent and the p >*e r futur n ".orung tLe sa rem j

t The se *tandard Nr te n dt.r. be tan e na wfb um, at in pa ru i-

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