ML20207J423

Informs of Completed Review of Event Re Low Oil Level in Essential Unit Substation Transformers.Review of LER & June 1986 Visit Determined Event Isolated Incident W/O Major Safety Significance.Related Info Encl

ML20207J423
Person / Time
Site:	Oyster Creek
Issue date:	07/23/1986
From:	Baer R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE)
To:	Ebneter S NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML20204F806	List: ML20204F801 ML20205J417 ML20206L834 ML20206L848 ML20207J423
References
NUDOCS 8607290053
Download: ML20207J423 (5)

Text

'

p***!vQ fg UNITED STATES 4

p, NUCLEAR REGULATORY COMMISSION

{ E WASHINGTON, D. C. 20555 E

\.....j JUL 2 31986 MEMORANDUM FOR: Stewart D. Ebneter, Director Division of Reactor Safety Region I FROM: Robert L. Baer, Chief Engineering and Generic Communications Branch Division of Emergency Preparedness and Engineering Response '

Office of Inspection and Enforcement

SUBJECT:

LOW OIL LEVEL IN ESSENTIAL UNIT SUBSTATION TRANSFORMERS AT OYSTER CREEK NUCLEAR GENERATING STATION

Reference:

Memorandum, Baer to Ebneter, 3-19-86, same subject This memorandum is to inform you of our review of the subject event. As we noted in our previous memorandum, we did not identify any similar transformer problems in our search of the LER, Part 21 or 50.55(e) reports. The previous memorandum also noted that we would visit the GE Medium Transformer Manufactur-ing Facility in Rome, Georgia to determine the scope of the problem and appro-

~

' '~

priate'IE action.

IE staff members from this branch and the Vendor Program Branch visited the manufacturing plant in June, 1986. They reviewed the manufacturing process, the quality control and the specific concerns involving this event. They also discussed previous transformer failures, corrective actions, and design detail with the GE staff. Based on this plant visit, the previous information pro-vided in the region inspection and discussions with the licensee, we believe 1 that this event was an isolated incident without major safety significance and therefore, an information notice is not required. However, some of the infor-mation obtained during this review could be of use in developing maintenancc programs. By separate memorandum we are providing copies of the Region I inspection report, the licensee's LER, and a summary of the information we i obtained during our review to the Maintenance and Training Branch, Division of  !

Human Factors Technology, NRR for their use in the development of the generic  !

maintenance programs. You are on distribution for that memorandum.

l l

l

Contact:

James C. Stewart, IE 492-9061 9yfN A

\

?

Stewart D. Ebneter -

We highlighted the following three items to NRR:

1) There was no record that the oil level had ever been checked except by the sight gage since it was delivered 17 years ago. Before the event, there was no scheduled plan to inspect the oil level for the duration of plant life.

2) The oil level gage was apparently trusted as accurate by the licensee without the necessary comparison with the oil temperature gage. Although GE stated that this has not been a major problem, they published an article (Ref. enclosure) in a trade magazine in 1971 on how to properly utilize transformer instrumentation.

3) The licensee did not keep complete records of the amount of oil removed for testing.

We do not plan any further action at this time.

Robert L. Baer, Chief Engineering and Generic Communications Branch Division of Emergency preparedness and Engineering Response Office of Inspection and Enforcement

Enclosure:

General Electric Reprint GER-2705 from April 1971 issue of Electrical South l

I i

1 MV K105

- 4  :.c.a g . ,; ,, ... ., ,

.;,.y9...t,

,- - . .. c. ~: , *

' .. . . . . .,  ;,, # .y.- n, p; .

y g%

.C a.g. . . . . -.,  ; ..

c.- ..- - -

a g- &.a . . , , . ,

,. J. .g' . - q: .: .,..x.

r . . -- . y- , ..n .!, . .- , - a

_.. ,.. .e.-

u.., 'p

' , . ' . .4 '_, .

~

4., ,.

c ,

. . ' . . y ~. , ,

..g. .-

.e . e

...- .. t 4 . ' -/1

. n.s . . ., .

g,.-1.').'[ .p +

, , .. 6 .

.j, 1 _".

,s , ,

s

,e;. +

.- - ~ ., y,-+. .

z . ,

3 '. s.. 'n.

+g- e,.

... . . & p:. . - - . . . -

, 4  ;

.t~ >

s. . . . . - , .. ... ' .

- Oi

. ' . , ..i.'3 * . O..f .&:.,c. , * . .

• ) ' ~2 -

1. .'.- . 2 :* .- , L. :. : * -

i. 'i 4-e 4 .

?:,

- Y[ - 'l -

l.

. . . , f .' _

.l

. . y -

8.

q..

u. e

_ e . < - ...:

=

.; - .;c .

'.n + r.

2. '- ' .  :,  : ..._ ..

-.-... ._a, .

. n + v i' .,- ,,f

, . - c.

g.- -

.& + e - ,

<e~ . -'

..$,. [

?

. . m y--

Q L _gl , .;l .c . ,^ cf 'c ^..#_ .

^ ? W: g . : y,.

' ' .l d-,am :

y:. ;_. ; ,..,

.n .. . ... .--w .. v. ..

.-~. _. y'l; Q,.; , fl ',.' .. ' .b,gpinen.?

I g,. .

- L  :

%i;. _ *

.; . - 1

+...>. ..

a < .; .

_ - .? .

.,s, ,

,. o

... . &. , . --. , . A - s

j. ' A , . '.

0 N. &,w. l ;s-

.L .. y .,:..

$ .n + ,

?

~

v _ l ' I;^ j . . b d '

. ,a- Q

~

y.

=. .

.' ., ..,g. .

l l

_e > . . y.-~z.,.._.__ .. . 7.,; , ~ . . .-

.y

. .. ,. . ~p , ;_. ; . y: _ ; -

l

.n? r. . , .

..n n n. ,. .

,_ l r.+

.....e.- . ,. .- . -, %s - (

f*..,,.' _, . s.--

- , .w

y. ..., y .,,:.x .,;.. v.,

-( .. ., . a, . -, . . ..._ > -u. -.

. +

.a . o ._ .:.. x y ; ';. :

. - e ,,*. ~.

\

..n, ;_. +

.. . ; ,, _g. ,_ _ ,.

n  :

.x,..- --

c., - . . -

4., . 4..._g~

a . .,.: e .:..

y

, . . . i'

.. : n ..

- . s.

+- - - . . - 1

-l,.,. ... N .-. . .p+.=3gi,- g ..,

_-.~- . s

.3.,.,.. . . . - . . , . . . . -

n. 5.,.

, . t.

.+ s.

y.

....y. , - s s

s . . e.;.a.. 9

.,,..r.,.

. . ' , a . . - >; - .'. .y t; . y. . s. ...:;-

W(( . - .:- ,y:

+ l, . L 8 - s. . . . . . , .

. ;.g. : .+ . ;. .

• w . :  ; .- *-

.. . , :.  ; _  ;- ,. - -y , # .

'. ..g .

, *' ,4 . p,- . .. 4 . . .

n.% + > . . ,  ;: u -

- -.r - ii- . .

~- .<-

s.a .

?

y,W.  ;.q 8 .. .. g; ? y

n..y .n-W. t,.;' .-e- .+ e : a.- i t .c q ;+~.:;._ ,L__..

. _ - J ! ,v ,- i,3 _ ' . , .  ;  ; -. ..'wf L . L' -,; ' ' L ' .,f * ' }' &-

,;,...,.;_. :,,.:-7r- ' , y . .:' oW:.)..: , ,.....'MQ.em . .;..>.-==an a

em . ..Q.

• . j. *y . , n

+ . . ..

L.

. ,. y % ;.,.) y _y

,,_ . . ~

,,;; l.:,n .

V [,9 . . g.:,

1.:*,

. ..s.-

. . *.u .

1 l

Alert to transformer .

gage md. cat. ions by R J. Ristow I

I i

l i

General Electnc Company Medium Transformer Products Department Rome, Georgia 30161 GENER AL h ELECTRIC t__ . _ - _ . _ _

1

,- . ~w

},

3

_ A ert to 0 5 transformer gage 32

)

y a,<

k.

By R. J. Ristow, Design Engineer, Gen- a 65 degree C rise transformer car. One common cause of transformer rying rated kVA, this oil temperature failure is operation without sulTicient l

• N I partrnent o ne$c"ofgi gage will read approximately 90 liquid. This can happen casily if no degrees C. At this temperature, the one watches the transformer gages

" Don't let those gages fool you" oil in the middle of the winding will and if the unit does not have a low is a key idea in reviewing with be about 80 degrees C and the wind- liquid level alarm. Transformer cool-electrical maintenance and operating ings about 95 degrees C, This cor- ing depends on liquid expansion personnel the operation of gages on responds to a 65 degree C rise over forcing the hot liquid into the top l all indoor and outdoor liquid-filled an ambient of 30 degrees C. For a 55 of the tube headers, where the liquid i transformers. degree C rise transformer, the oil gives off its heat to the outside air All too often, a concerned electrical temperature gage should read about as it flows down through the tubes.

l superintendent will call the trans- 80 degrees C under normal load at The tubes should be hot at the top ,

former manufacturer when an oil an ambient of 30 degrees C. and get cooler as they progrew f temperature gage reads 65 degrees C Transformers aiso are supplied with dow nward.  ;

and the transformer is carrying only two other gages, the liquid level gage if for some reason, such as a leak, half load. He is afraid to load his and the pressure vacuum gage. If there is insufficient liquid in the tank transformer any more, because the properly read and evaluated, these to reach the top opening of the tubes nameplate states that it is suitable gages can show when something is when it starts getting hot, the unit for a certain kVA at 65 degree C about to go wrong, thereby prevent- will burn itself up. The oil tempera-rise. ing an electrical outage. ture gage may not even indicate The key word, of course, is " rise." It is important to note that all any trouble, because the sensing bulb It means that the transformer wind- three gages must be read before one will be out of oil, reading only the ings will enjoy a normal life if their can accurately predict the condition temperature of the air space. Both the temperature does not exceed 65 de- of the transformer. Both the liquid pressure gage and the liquid level grees C over the ambient or surround- level and the pressure inside the gage also will read low. So for an ing temperature. If the surrounding transformer are determined by the inexperienced person.everything will air is 86 degrees F or 30 degrees C, temperature of the insulating liquid. appear normal with all gages reading then the actual temperature of the High temperatures are accompanied low. What he neglects to take into windings could be 65 degrees C + 30 by high liquid levels (because of consideration is the load on the degrees C, or 95 degrees C. liquid expansion) and, consequently, transformer.

This may not mean much, of high pressure. If, for instance, the if all gages are reading low, then course, to operating personnel. They oil temperature gage reads 90 de- the load should be very small or the see only an oil temperature gage; grees C and the liquid level gage day very cold. If the surrounding air no one has told them what it should reads high but the pressure gage is warm and the load is moderate ,

read. They know it has some rela- reads zero, then a transformer leak to heavy, then the oil temperature j tionship to the winding temperature, may exist. If no leaking liquid is gage should read a temperature in- l l but what that relationship is, often present, the leak is probably in the crease, the liquid level gage indicate is not known. As a general rule, for air space above the liquid. a high level, and the pressure gage I

1 4.

1

>** +

Potential trouble may be averted by the proper indicat'ons analysis of gage readings show some positive pressure. The the oil heats up. The temperature them, but not with some applied table illustrates normal gage readings of the oil can rise even after load is reasoning and analysis. A person with various conditions of ambient reduced because of this time lag. If can spot potential problems, avoid the ambient temperature falls below trouble, and assure himself of power temperature and load.

Sometimes it becomes necessary 30 degrees C (86 degrees F), then system reliability by being familiar to supply short time overloads to a overloads are permissible (approxi- with transformer gages.

transformer. When this happens, the mately one percent extra kVA per 1 oil temperature gage cannot serve one degree C lower temperature).

as a loading guide. It takes two to For ambients above 30 degrees C, ,

four hours before the full effect of a the kVA output must be decreased l load registers on an oil temperature 1.5 percent for cach one degree C gage. This is because first, the winding higher temperature.

and core have to heat up, and then Gages can fool, cven if one watches Oil temperature Liquid tevel Pressure l Ambient Load vacuum gage J gage gage 0

" - +

L H 30*C None 30' \ o o o

n 65* j _ j ,

Moderate o / /

30* C 0

90 L H - +

30*C Rated kVA / / /

0 35* - +

L H 0*C Moderate \

0

+

45'\

L 4

f H -

20*C' Rated kVA l

'At this tempera'ure, the transformer could carry 50 percent more load than the navneptate indicates.

The table shows normal gage readings with various conditions of ambient temperature and load.

Reprinted from April 1911 assue of ELECTRICAL SOUTH 1

1