Oil Filled Transformer

[ccov]

We have a 1986 vintage Westinghouse 2000KVA 23kV-480V 65 deg C rise transformer showing some interesting characteristics under a thermal inspection (please note there are no oil analysis or service issues):
1. An entire bank of cooling fins appear clogged/disconnected. How is this possible? Additional cooling fins at the same level are fine (the 1.5" tube/manifold for the fins is clogged). I would assume material large enough to clog this would cause much bigger issues.
2. The exterior shell of the transformer shows elevated temps (155 deg F, 40 deg ambient) on the side of the clogged fins (makes sense, right). Should I be concerned?
3. The oil temperature gauge is located on the radiator that is clogged, rendering it useless.
Does anyone know who to contact for Westinghouse transformer support?
Thanks.......

 

[davidbeach]

ABB took over that portion of Westinghouse.

 

[Laplacian]

It sounds like low oil level. Are the opposing top manifolds at exactly the same fluid level; transformer sitting level, etc.?

Is that 40 deg F or C ambient? The 155 deg F operating temperature is only 68 deg C which doesn't sound like a problem, but the oil is stagnant and could be sludging up on the non-circulating side.

I would not top the oil with the tranformer energized.

 

[ccov]

Thanks for the replies.
Ambient is about 40 degF
That's what has me puzzled, the transformer is setting level, but the 2 other radiators are circulating normal. the liquid level gauge is between the "25deg" and "LO" range. Your right, it does sound like it is low on oil, perhaps a topping off (de-energized) is in order ....

 

[BJC]

Check the bank that is "clogged" closely. I would suspect a blind flange in the connection. Maby it leaked at one time and that was the fastest way to fix it.

 

[Zogzog]

Its probally just a level problem but you may want to draw a oil sample to see if you have anything else going on there.

 

[EMT01]

Assuming the level is OK and the fluid is mineral oil, then I would look at the oil quality test results (specifically moisture content). If moisture is elevated, then look to the acid neutralization number and if also elevated (.20 or higher for this class of XFMR) then sludge may be forming and causing your circulation problems.

 

[capuchi]

I agree with EMT01. Also include chemical analysis of the oil. I presume this is an outdoor unit so check for some telltale leaks on the cooling fins before topping the oil. Hope this is of help.

 

[ccov]

The oil test results are all acceptable (ACID .020), and the unit has an excellent history. I just wish I knew if a 140degF exterior (peak) temp was cause for concern. the definition of temp. rise is ""the average temperature of the windings and insulation above the existing ambient temperature"".
So ... part of me says the oil is part of "the insulation", the oil temp has be very close to the tank exterior (1/4" steel should not provide much insulation), so we are still within the temp. rise rating of the transformer.
ANOTHER part of me says if you are reading 140degF on the tank exterior, the windings would be much higher.
Knowing that temp gauges read the oil temp, is that what is used to determine "temp rise" rating? (the oil temp).
This is a very difficult question to answer.

 

[controlsdude]

If I had sludge in a oil filled xfmr, would not you take it out of service and have the xfmr dried out and retanked?


I am just curious

 

[Zogzog]

"Knowing that temp gauges read the oil temp, is that what is used to determine "temp rise" rating? (the oil temp)."

Yes, the temp gauge reads oil temp near the core and should read higher than the (peak) ambient temp. But the gauge + ambient (In the room) should not exceed the max rise rating.

140F is not very hot, your problem seems to be level and possible sludge clogging cooling fins

 

[Zogzog]

"If I had sludge in a oil filled xfmr, would not you take it out of service and have the xfmr dried out and retanked?"

Usually you can use a filtration rig to remove the sludge, but the problem is not the sludge, its what is producing the sludge, thats what needs to be focused on.

 

[EMT01]

I wouldn't typically untank a three-phase power transformer for a moisture related problem. However, it depends upon several factors; size; criticality of the feed; accessibility; etc. If the unit is significantly beyond the IEEE / ANSI limits for in-service oil you may want to:

1.) Repair the cause of the moisture ingestion.
2.) Have the unit de-hydrated (on-line is a possibility)or,
3.) Replace the fluid

Either way you go, you should have a Furanic Compound Analysis performed to determine the amount of insulation degradation before replacing or processing the fluid. Once the repairs are completed, full electrical testing should be performed at the first available opportunity by a qualified electrical testing firm.

 

[unclebob]

Is it possible the radiator valves be closed?
Top or bottom one.

 

[ccov]

Thanks for everyones advice, I am going check the level and add oil if necessary and pull another oil sample .... and take it from there.
There unit doesn't have radiator valves.
The manufacturere seems to think the level is low as well. At 25degC, the oil should be midway between the top manifold.

 

[EMT01]

Don't forget that when topping off fluid, verification of the fluid could be necessary in the event the gauge is out of calibration. Sometimes it is necessary to adjust the float rod after taking an actual measurement of the fluid level. Also, be sure to make sure if the unit has a N2 blanket it is purged to less than 2% O2.

 

[pocketchange]

I would also make sure that the transformer is level. If for some reason the foundation hasn't moved to make the transformer lean. Also I would look at the history to see if any internal work has been done. I have found radiators that have had rags stuff in the openings during some internal inspections.