Message Board Thread - "Possible Transformer Problem"

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Possible Transformer Problem Ron Cooper 2/5/2005
I have found this over the last week. On this day it was -15 C degrees. The cooling tubes of the transformer are only half working. Li1 ranges from -13 to 11.8, Li2 is -3.3 to 9.6, and Li3 is -12.4 to -4 degrees. I am waiting for some information to get back from the manufacturer but from what I can tell it seems as thought the outer part of the cooling tubes has no oil flow through them. What should happen is hot oil enters the top part of the tubes, then as it cools it flows down the tube and enters back into thw transformer at the bottom. A few days later we had a warm patch of weather so I went and rescanned the transformer. I will add another post for this image.
 
Re:Possible Transformer Problem Ron Cooper 2/5/2005
In this shot Li1 is now 18.3 to 20.4 degrees, Li2 is 11.7 to 19.8, and Li3 is 6.9 to 10 degrees. From a few other shots I have taken it seems as if there may be water in the bottom of the transformer. With the temperature being so cold the water would freeze and block the flow of oil out the bottom of the tubes. When the weather wams up the internal temperature of the transformer melts the ice allowing the oil to flow. I have suggested we do oil samples to find out if this the problem. Another point is this would not have ben found if the scan was done when the weather was warm, it would have appeared as if the cooling tubes were working normally.
 
Re:Possible Transformer Problem electricpete 2/5/2005
Maybe one other possibility is that the cold weather increases the oil viscosity which for whatever reason causes the difference between hot and cold behavior.
 
Re:Possible Transformer Problem Manuel 2/6/2005
Hi Ron and Pete.

I agree with pete about viscosity.

if you think there are water inside, take an oil sample, open just a little enough to let drops coming out, maybe instead oil, the fist drops should be water, in wich case you conclusion will be confirmed.

maybe there a lot of mud.

let us know.

r cruz
thermoimagen
 
Re:Possible Transformer Problem Doctir bob 2/9/2005
Many transformer cooling systems are designed to stage so that only a portion works in colder weather. You may want to check the particular design of this transformer. The thoughts mentioned in other postings are possibilities, but it could also indicate normal operation.
 
Re:Possible Transformer Problem Manuel 2/10/2005
make sense.

If you look at the backgroung wall, the first image have minus 5 celsius, wich can indicate that transformer needs some heat to maintaing oil viscosity that allows flows.

the secong thermogram the background wall shows around plus 15 celsius, in this case the oil maybe need to be cooled down.

so, then, maybe there are some thermostat inside transformer. please let us know.

regards

PS in mexicali where the colder temps are 4 C and just 2 or 3 days a year never will see this stage effect. thanks for images.
 
Re:Possible Transformer Problem electricpete 2/11/2005
This transformer looks to have no pumps. So the stages might be: no fans, 1/2 fans, full fans as oil temperature increases.

The only way I can see this affecting the image is if there were fans blowing crosswise accross the outer bank of fins but not the inner bank. It doesn't look to me like that's what's going on but you never know. Maybe the thermographer noticed whether any fans were running?
 
Re:Possible Transformer Problem Ron Cooper 2/11/2005
I have checked with the blue prints we have on the units, there is no restrictions in the cooling tubes. There are no fans on the units and have also seen a sample of the type of oil in transformers we use. It is very thin, almost like vegetable oil. At present the pressure guage is to close to zero or negative to allow for a oil sample to be taken, and the level guage indicates there is enough oil inside. The electrical distribution dept. we have has told me there is no concern with it as it is well belove the 80 degrees alarm point. Lately we have been having a warm strech of weather. Next week it is supposed to get cold again. I plan on doing a test of the units. I will get a series of shots of the unit this includes ones along the length of the cooling tubes, at less than one meter, both top and bottom and from both sides. I will then use a heat gun and blow hot air at the tubes to warm them up, if I start to get flow I do beleive that will prove there is water inside. I hope to let everyone who the outcome next week.
 
Re:Possible Transformer Problem electricpete 2/12/2005
"well belove the alarm setpoint" That's a funny typographical mixture of below and above. Although it was clear from the context you meant below.

The comment on viscosity was not that you may have the wrong type oil but that almost oil oil gets thicker at cold weather so more likely to have flow problems during cold weather.

Somewhere I think you mentioned the transformer was at zero pressure or under vacuum. That in itself would be a concern for the transformers at our plant which all have nitrogen blanket to assure continuous positive pressure.





 
Re:Possible Transformer Problem Ron Cooper 2/12/2005
I haven't gotten a lot of info from the manufacturers but from what they told we, I get the impression that there should be a positive pressure most of the time. Under cold conditions -20C and below the fact that the oil contacts can cause a negative pressure. This in my opinion doesn't seem right because if there was a leak and the pressure was negative it would suck air in. But then again if the pressure was positive and a leak developed the expansion and contaction of the oil would still suck air in eventually. I need to find out a lot more info.
 
Re:Possible Transformer Problem Ron Cooper 2/22/2005
I have done a few more tests on the transformers in the previous scans. On the day I checked it was -20C again, this time I took shots of the upper and lower connector tubes and the cooling fins as well as digitals of all the guages. Then I used a heat gun to heat up the bottom section of the fins where there seemed to be no flow. After an hour of heating I found that there was no difference in the cooling that was being done with the radiator tubes. This ruled out the chance of water being in the tubes and restricting the flow. I was also told from the manufacturer that if that much water was in the transformer it probably would have had a catastrophic failure (blow-up). After analysing the IR shots I noticed that the cooling effect at the top of the cooling tubes in the inlet header was very dramatic, it started at 20C and within a foot it dropped to -10C . At the bottom the same effect was happening. This is most likely because of the slow circulation of the oil in the tubes. The pressure guage at the time was reading -2 lbs so there was no oil samples taken and we will check the guage again when it warms up to verify that the pressure increases, this will determine that there is a proper seal on the cabinet. The oil level guage was reading a little low from the info I got from the manufacturer, but not enough to be worried about. The low mark is at 2.25" and the high is at 3" a difference of 3/4 of an inch with one inch requiring 6.6 gallons of oil. Basically I have found that in this type of situation as long as the transformer is not heating up and there is any indication that the oil is being cooled there is no cause for concern. Hopefully this has helped everyone else as it has been a good learning experience for me.
 
Re:Possible Transformer Problem Dan 3/2/2005
Please remember that at this temperature, the insulating oil level will go down. It becomes much more dense. As the oil temperature increases, the oil level will go up.
I was not able to download the image, but from what I could see from the small image on the board, it looks as if the oil level is too low to maintain proper oil flow through the radiators. At this temperature, cooling of the transformer is not a major concern. As the transformer generates heat, the oil will flow naturally, not requiring pumps to cool. Pumps are typically installed to assist cooling when the environment requires additional conditioning.
My other concern would be that the transformer is not level. If the concrete pad is not absolutely level, and the oil level is low, it could effect the natural flow of the oil.
 
Re:Possible Transformer Problem Alan Toy 3/2/2005
Ron,

Dans response reminded me of an utility infrared presentation that I had attended: Apparently, the tolerances at the top header pipe to the invidual radiator fins were not consistent - some of the fin pipe ends terminated higher in the header piping; thus, some fins would not fill as soon as the fin that terminated at the base of the header. This condition existed even with the correct oil level in the transformer.
Good Luck,
Alan
 
Re:Possible Transformer Problem daryl 3/2/2005
Ron,
A couple of things to think about that many have mentioned before. During colder weather the viscosity of the oil will become lower and make the oil more dense. This cold weather "shrinking" will make the oil level in the xmfr appear to be low - sometimes low enough to drop the level below the upper tube and could compound the issue if the xmfr is not level. When the temperature drops I usually make sure that I check the xmfr oil level with my camera, check the level if possible, check all the tubes and note if different hot and cold areas exist in the tube pattern, ask the substation manager if the oil has been pumped (rotated in the xmfr)recently, note the load on the xmfr and most of all take images in different temperature. Without a pattern developing - one tube is during all conditions is consistently a low temperature I would not give an opinion concerning the effectiveness of operation. On the other hand if the oil level consistently drops to a low level at low temperature - below the upper tube on cold days visit with the xmfr manufacturer concerning safe oil operation levels adding oil might solve the problem. Watch hot days the opposite hot oil effect could cause oil spills/overfills.
 
Re:Possible Transformer Problem RonFrend 3/10/2005
Have you considered that the oil may be dropping below its POUR POINT? When oil gets very cold the it reaches the pour point when waxy or parafinic components start to solidify and develop a matrix structure.

I suggest taking a sample and just let it stand at the low ambient temperatures and see if it still flows.
 
Re:Possible Transformer Problem kittler 3/10/2005
I spent five years working for the "transformer consultants". This situation is more common than one may realize. In the cold environment, 0°C, the mineral oil does contract as the viscosity goes up. When the transformer runs between ambient upto about 20°C there is no need for the oil to flow through the convection process to cool the unit, since we are well within normal operating ranges. As the ambient temperature rises, or load condtions increase on the unit, the oil will expand and rise to flow through the radiators for convection cooling. If this unit were running at 45-50°C and oil was not flowing through the radiators, we would have a problem. We used to consult that for every 10°C above 50°C the transformer was allowed to run at, it would reduce the units life 50%. Keep in mind that if the oil level was above the radiators at -15°C, then in the summer months the oil would over flow and lead out of inspection ports or the top filter press valve.
 


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