ML20137M185

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Rev 1 to Open Circuit of Current Transformer Secondary
ML20137M185
Person / Time
Site: Clinton Constellation icon.png
Issue date: 10/17/1983
From:
SARGENT & LUNDY, INC.
To:
Shared Package
ML20137M160 List:
References
19-BD-5, 19-BD-5-R01, 19-BD-5-R1, NUDOCS 8601280211
Download: ML20137M185 (8)
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OPEN CIRCUIT OF CURRENT cue nom 9-BD-9 SARGENT ALUNDY TRANSFORMER SECcNoARY n ., 1 oat.ToJ17/a 3 '

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. c.ent ILLINOIS PCWER COMPANY p,,p., o tofb _,,,(had yr pgD l o,s./cyf r/n _

Protect CLINTON - UNIT 1 g,,,,,,d n, h[ fyd 37en lcate /v//r//)

Pros. No. 4536-00 Ew.u No Approved by My[# [. yer CYO

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U FILE Alo.19'@

I. REVISION STATUS Rev. 0 1/4/83 First issue all pages.

Rev. 1 10/17/83 Second issue all pages. The revised material

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is denoted by linleftmargin. This revision deletes information from two referenced Q.A.

calculations which have been ' voided, and includes two more pieces of equipment into the analysis.

\ d II. PURPOSE

. The purpose of this calculation is,to determine if the open circuiting of the secondary of the non-Class lE metering or bus duct differential relaying cts at the main and reserve feed to the 4.16 kV ESF switchgear would cause a condition adverse

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to safety-related circuits, since the non-Class lE CT secondary wiring is bundled and/or in close proximity to C.'. ass lE wiring internal to the switchgears. The open circuiting of the non-a

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Class lE cts analyzed are identified in Section IV.B of this 8

, calculation.

E i UNCONTROLLED COPY

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REVIEW METHOD D c b + l.-l S*

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8601280211 060124 PDR ADOCK 05000461 A PDR

O cs For OPEN CIRCUIT O'P GURRE!!? Caic No 19-DD-5 SARGENT iLUNDY TRANSFORMER SECONDARY H ., 1 0.te10/17 /8 3

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. ci.en ILLINOIS POWEP. COMPANY Prepared b, G. A. POLETTO Date/4

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Pro,ect CLINTON - UNIT 1 Reviewed by  ? Oase  :

Proi. No. 4536-00 Epp No. Approved by Date III. REFE RENCES ~

1. " Peak Voltages Induced by Accelerated Flux Reversal in.

Reactor Cores Operating Above Saturation Density" by Theodore Specht and E. C. Went: in AIEE Transactions, May 1946, 2 Insulation of Electrical Apparatus book by D. F. Miner, 1941, Chapter III, " Factors Affecting Dielectric Behavior".

3. "Overvoltages in Saturable Series Devices" by A. Boyajian and G. Camilli in AIEE Transactions, 1951, pp. 1845-1853 4 ANSI Standard C57.13-1978
5. ICEA-NEMA Standard S-66-524,
6. Q A. Calculation 4536-EAD-1, Rev. 2, dated 8/12/81.

l7 S&L single line drawing: E02-1AP01, Sht. 004, Rev. C, 4/29/83 .

8 S&L Relay and Metering Diagrams:

E02-1AP12, Sheet 011, Rev. P , dated 4-7-8 3

' E02-1AP12, Sheet 013, Rev. M, dated 4-7-83.

E02-1AP12, Sheet 016, Rev. J, dated 7-22-83 s 9. S&L CT excitation curves:

Westinghouse 459341, Rev. A, for 5000:5A CT' 8

a a Westinghouse 536932-A, Rev. A, for 800:5A CT .

j Westinghouse 622004, Rev. A, for 4000:5A CT I Westinghouse 666818, for 2500:2.5A CT.

10. Memo of telephone conversation between Ed Horn of Westinghouse and G. A. Poletto of S&L, dated 12/30/82
11. NCRs 5426; Rev. 1, dated 8-9-82 5425, Rev. 1, dated 8-9-82 5453, Rev.,1, dated 8-9-82.

C.io Fo, OPEN CIRCUIT Or CURRENT coc so 19-BD-5 SARGENT a LUNDY TRANSrORMER SECONDARY a .. 1 a.ie 10/17/a 3

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" ~ - + - x i wei,-sei.i.o =l]- ! N . -ue .-a.i.i.a r.y. 3 or 8 C1ent ILLINOIS POWER OMPANY Prewed by ' G. A. POLETTO cai.fc4 y /G Proiect CLINTON - UNIT l Reviewed av 0.te Proi. No. 4536-00 Em.ip No. Approud av Oais III. REFERENCES (Cont'd.)

12. ANSI /IEEE C37.90-1978, " Relays and Relay-Systems Associated .

j with Electric Power Apparatus".

h 13. "The Effects of Electric Discharges Between Electrodes Across Insulation Surfaces", by Lyon Mandelcorn, AIEE Transaction on Power Apparatus and System, August 1961, pp. 481-494

14. Buchanan "Electrolog" January 1971 IV. DATA A. Test Data on Some Typical cts l.(Reference 1, dated 1946)
a. 2500/5A CT Voltage Class 5000V Westinghouse Type H-5

) Accuracy Class 0.3D-0.1, 0.5, 2 Peak secondary open circuit voltage with rated current in the primary: v oc = ll,000V i

1 b. 5/5-600/5A CT voltage Class 5000V Westinghouse Type. CT-5 i Accuracy Class 0. 38-0.1, 0.5, 2 i

Peak secondary open circuit voltage with rated current 4

in the primary: V oc = 1800V

}z 8 2 (Reference 10, dated 12/30/82) i m l 3 a. 1200/5A CT Westinghouse Type RCT for medium voltage swgr.

!  ! Peak secondary open circuit voltage with rated current

in the primary
V = 25,000V oc i

, b. 600/SA CT Westinghouse Type RCT for medium voltage swgr.

1 i Peak secondary open circuit voltage with rated current in the primary: V = 12,000V oc

c. 400/5A CT Westinghouse Type RCT for medium voltage swgr.

Peak secondary open circuit voltage with rated current in the primary: V = 4000V' oc l

Cales Fo, OPEN CIRCUIT OF CURRENT _

caic No 19-BD-5 SARGENT LUNDY TRANSFORMER SECONDARY

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! Page 4 of 8 Ci.en II.LINOIS POWER COMPANY buared by G. A. POLETTO Date/OS 7/;'l Prsiect CLINTON - UNIP 1 Reviewed by Date Prea No. 4536-00 duu.o No awroved o< oei.

IV. DATA (7ont'd.)

S. Rating of Existing Non-Class lE cts Whose Open Circuiting is Analyzed

1. On the Main Feed to 4.16 kV Buses lAl and 1B1 (Ref. 9 )
a. 2500-2.5A CT with accuracy class C-400 for bus duct differential relay,
b. 800-5A metering CT with accuracy class 10H50,
2. On the Reserve Feed to 4.16 kV Buses lAl and 1B1 ( Re' f . 9 )

4000-5A CT accuracy class C-200 for bus duct differential" relay.

3. On the Main feed to 4.16 kV Bus ICl 5000-5A CT for bus duct differential relay.
4. On the Reserve Feed to 4.16 kV Bus 1Cl 4000-5A CT for bus duct differential relay.

C. Insulation Requirements for the cts, Cables and Other Devices

1. A current transformer is required to withstand a secondary voltage of 3500V peak for 60 seconds (per ANSI C57.13 -

, Ref. 4 ),

a I 2 600V class cables are required to withstand 3500V rms for

! 5 minutes (per ICEA-NEMA Std S-66-524 - Ref.5). '

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j 3. Terminal blocks and test switches are required to withstand twice rated voltage plus 1000V rms for 60 seconds.

Terminal block rated 750V (Ref. 12, p. 42) 750 x 2

  • 1000 = 2500V rms Test switch rated 600V 600 x 2 + 1000 = 2200V rms l

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con so,

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OPEN CIRCUIT OF CURRENT k cm. N o_ 19-BD-5 SARGENT a LUNDY TRANSPOnnEn SECONDAaY ---

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, ct..n ILLINOIS POWER COMPANY Preparea bv G. A. POLETTO Date/c/f 7/C Proiect CLINTON - UNIT 1 nes,ewea av lcate Approved by Date Proi. No. 4536-00 Euwo No.

V. ANALYSIS OF EFFECTIVE OPEN CIRCUITED CT SECONDARY Determination of the peak voltage that would occur if.the secondary of any of these cts in question were to become open circuited with full load current flowing in the primary with any degree of accuracy is difficult without actually performing a test on each CT. This peak voltage is a function of the turns ratio and the design of the core of the transformer.

Even with,the same turns ratio, the peak voltage may vary greatly from one CT to another due to differences in the core design. Since the manufacturers are reluctant to perform tests on cts with secondaries open circuited, there is very limited test data available to'compa're with the cts in question. liowever, it can be seen from the available test data that the peak voltages may range from 2 kV to 25 kV. If the open circuit  ;

of ,the secondary goes undetect'ed for an extended period of ,

time, these peak voltages will most likely cause an insulation failure.

From the industry requirement for the insulation of the devices j given in Section IV.C, and that breakdown voltage' for insulation, materials is an inverse exponential function of time (Ref. 2 ) ,

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[ we may draw a typical curve for each of the four insulations

$ involved in the CT circuitry as shown below.

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I ge,p,OPEN CIRCUIT OF CURRENT caic Na 19-DD-5 l SARGENT x LUNDY TRANSFORMER SECONDARY R ev.

1 04teLO/17/8 3

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" * * * * " N; Listv-Re64:ed Non-Lf ety-R elated Paqe 6 of 8 ct.en: ILLINOIS POWER COMPANY prepared by G. A. POLET10 Data /od V5'3 '

Pro,ect CLINTON - UNIT 1 R viewed bv l cate l Pro No. 4536-00 Ecu.o No. Apo,oved bv l 0 ate V. ANALYSIS OF EFFECTIVE OPEN CIRCUITED CT SECONDARY (Cont'd.)

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CABLE l

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< k N l

3.5 x 4 kV 2.5kV x d 0 I 3 2.2kV x d Term.,Blk.

1 Min.

. Test /

Switch ,

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. LOG TIME -

i From this figure we can. expect either the CT insulation, the terminal block or the test switch to fail before the cable

, insulation. If the CT fails, it would occur near the ungrounded j j CT terminal which is exposed to the full peak open circuit voltage j and would most probably involve a sparkover between terminals or to

ground. The arc will quickly form a carbon track (Ref.13) which will j j provide a low resistance path to ground. !!avina both te.rminals ground +

2 will short circuit the secondary of the CT and alleviate the i high peak voltage. The secondary current will only be a few amperes and will not cause damage to the ground path.

The safety and non-safety terminal blocks or test switches are physically separated (not touching) from each other. If the I . terminal block or test switch fail, it will involve an arc from

I w ro, - OPEM CIRCUIT OF CURRENT Cale. Na 19-0D-5

. SARGENT2 LUNDY TRANSFORMER SECONDARY Rev 1 Due10 /17 /9 -

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ct.en ILLINOIS POWER COMPANY Prep.,ed by G. A. POLETTO Oue/GId?3

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) he,u CLINTON - UNIT 1 Reve*ed b, I ho,. No. 4536-00 Ewa No. Approved av om i

k V. ANALYSIS OF CFFECTIVE OP.':N. CIRCUITED CT SECONDARY (Cont'd.) f l  :

i the terminal connected to the ungrounded CT lead to the grounded . r terminal. This are will quickly form a carbon track (Ref. 13) which will act as a low resistance path for the CT secondary current. This short circuits the secondary of the CT and alleviates the high peak voltage. The secondary current will l

I only be a few amperes and will not cause damage 'in the ground path.

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l For the metering cts the open circuit condition would be detected

during the next meter logging operation and corrected.

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' For the main (RAT) feed differential relay CT to any of the ESF f buses, the differential relay will trip immediately and transfer the ESF buses to the reserve source or the diesel generator if l

4 the current through the open circuited CT is greater than the minimum sensitivity of the relay. However, if the current is I

less than the minimum relay sensitivity, open circuiting of the CT will not cause the breaker to trip but the relay will

! still be able to detect and trip for any f ault occurring. within its zone of protection.

For the reserve feed differential relay CT to any of the ESF e

buses, the dLfferential relay will trip immediately and transfer 4 .

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} the ESF busea to the main source or the diesel generator if  ;

.j the current through the open circuited CT is greater than the ,

a j minimum sensitivity of the relay. If the current is less than j the minimum relay sensitivity, open circuiting of the CT will i not cause the breaker to trip, but the relay will still be >

able to detect and trip for any fault within its zone of l

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protection.

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    • ** Ca. ra, OPEN CIRCUIT OF CURRENT caic. g. 19-BD-5 i

i SARGENT ELUNDY TRANSFORMER SECONDARY Rev 1 Oa:JO/17/03 l - .co m .

8 c"<^"" - X! s.t.t,-a. tar d Non-Saf ety- A elated Page8 of 4

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- ILLINOIS POWER COMPANY Pre w ed bv G. A. POLETTc Date/d ///b3 client l l Date Pro,ect CLINTON - UNIT 1 Rev.evoed by 1

. 1 Equ.o No. Approved bv l Date i

! Prai No. 4536-00  !

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., VI. CONCLUSIONS r i

We conclude that open circuiting of the metering or differential [

i relaying cts is not expected to result in a condition adverse to i safety-related circuits.

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