Hi guys,

During our routine IR checking of transformers,we come across this image!! Seems like some of the plates are blocked or damaged.. What do you think? Will there be any immediate cosequences due to this problem?

Have a nice day!!

I'm assuming this is an oil filled transformer and you are looking at the cooling tubes? If so, YES, this is a problem because it can result in the transformer overheating. Industry guidelines suggest a 10C rise in oil temperature results in a 50% loss of transformer life! Expensive.

Often the cause of this problem is low oil, but we have also seen any number of other root causes including valves being closed, rags stuffed in the tube, and out of level. I would strongly recommend you followup to find the root cause and check again after repairs have been made.

Thank you John,

Yes, itz an oil filled transformer and we were looking at the cooling tubes..

If 10ºC rise will cause 50% of transformer life, then itz a real problem..

But is there any acceptable range of temperatures for these transformers? Mine is ONAN/STC make; 1000KVA, 13.8KV/400V, 1440A transformer..

Have a nice day!!

YES! All transformers are rated to operate at a certain temperature and a certain rise over ambient. Check with your manufacturer for the spec on this one.

Practically speaking, the factor of 2 change in insulation lifetime per 10C is only important when you are operating at a temperature where thermal degradation is significant.

Oil-filled transformers are generally rated for a 55C (older) or 65C (newer) rise of average winding temperature over ambient temperature (listed on the nameplate). Additionally, there may be a 10-15C allowance for hot-spot rise over average winding temperature rise. These are continuous ratings assuming a 30C ambient with 40C daytime peaks. Top oil temperature often is in the same neighborhood as average winding temperature.

Your transformer is likely equipped with top oil temperature gage and estimated winding hot-spot temperature gage, including alarms. Often oil temp alarm is in the neighborhood of 90C. Your temperatures do appear much lower at the time of the survey (43C highest visible at external surface of the top oil header ...I'm guessing top oil temperature is no more than 10C above that). Of course if load and ambient temperature changes, everything changes.

quote:

Of course if load and ambient temperature changes, everything changes.

...and given the location (Saudi Arabia), I suggest that ANY restriction of cooling is a problem that warrants further investigation. I agree an increase in temperature is typically not instantaneously damaging but degradation does increase, even if incrementally, as temperatures increase.

Hi guys,

Thank you for the valuable information..

Actually this transformer is inside an air-conditioned room and now the temperature outside is also very cold.. So there may not be any big problem for 3-4 months..

But i just want to know how frequent people are doing thermal surveys on their Transformers?

Have a nice day and Happy New Year in advance!!

You don't happen to have an air conditioner fan blowing on this transformer do you
I thought this thing was outside. Inside an air conditioned room would make me want to hang some ribbon around and see what the air currents inside the room are doing.Looks to me like one is blowing air on the cooling fins.

Dave

Dave,

Itz not like that.. The room is airconditioned.. There are 10 transformers in that room and the air is not blowing directly to the cooling fins anyway.. We didn't find any problem for the rest of the transformers.. Only this one is showing difference in fin temperatures..
Sorry for confusing you!!

Have a nice day and Happy New Year!!

hello to all
the company i work for just had insallments of new transformers and while on my routine route I noticed that the heat exchangers were warm and cool on certain corners. No blockage and good on oil level. so i put a level on the transformers and was out of level. The oil in the transformers was not reaching the fins on the high corners. your conversations really helped out

Thanks from JoDan.

I see these things periodically. If the transformer is not under high load, it may never matter. Sometimes the oil gets enough dirt so that the radiator tubes clog. The oil should be sampled and checked for impurities. The oil level should be checked and, as InfraSloop pointed out, the transformer should be checked for level. Oil level and transformer levelness are the typical issues here. The radiator tubes openings are often not at precisely the same heights. This means that low oil or out of level can produce the pattern seen here.

quote:

If the transformer is not under high load, it may never matter.

The danger is when one sees it while loads are low but fails to foresee higher loads coming in the future.... We see many outside that are out of level in the winter but by summer the settle down and (mostly) go back to level. I also here more and more reports of folks finding low oil related to oil samples having been pulled without anyone replacing any.

Take a look at the image. The tops of the cool tubes appear to enter the transformer at a level higher than the warm tubes. In addition, the surface temps diminish right above the top of the warm tubes. This appears to be a case of low oil. The heat line and temperature pattern should be checked all around this transformer. This can probably be used to determine whether it is low oil or out of level.

trending should be a factor when the transformer is at a higher load than other days and seasons. that is why i caught the two new transformers resently installed. getting a base line for a certain transformer soyou can watvch the heat rise or fall.