Deenergized Transformers in Winter

[brupp]

I am looking for anyone's personal experience with shutting down their transformers for the winter. We have some peaking power plants with multiple Generator Step-Up transformers and would like to shut down all but one GSU for the off-season (winter). Our GSUs have conservator tanks and are located in central US, where minimum temp may reach -30C. I read the manufacturer's literature and they warn against letting the oil level go too low due to low temperature due to the possibility of air entering the main tank. I really don't want to keep a transformer humming all winter drawing 120kW in no-load losses, costing over $3000 per month in demand and energy charges.

Has anyone come up with a solution to this issue? I've considered rotating transformers regularly but haven't figured out a way to determine the actual oil temperature or how long it will take for a transformer to cool down after being energized and warmed up. Any input would be appreciated.

 

[BJC]

What ever you do I would not rotate them. Cycling them hot and cold is the worst thing you can do. If you don't have leak now cycling them may be the best way to develope one.

Is there a way you can cover and heat them? I have built shelters for things ( not transformers ) using insulated kelly closures.

http://www.kellyklosure.com/index.html

There are also insulated "blankets" that you could use for wrapping them up. Look for the "blankets" use to keep concrete from freezing when it is place in cold weather.

You clould try that along with a space heater.
How big are your transformers?
You can heat them internally using a welder connected to the secondary windings. You will put less power in it than by energizing it with no load.
If I were doing this I would put an alarm system on it. Heating the transformer up and cooling is not good.

 

[jwerthman]

I have worked with several utility clients that have situations identical to yours and some choose to just leave the transformers de-energized when the generators are not on-line, which is usually over the cold winter months. I don't really think it's a good idea, for the reasons you have stated, but my clients say they have had no problems.

I have on some projects in the past used a low voltage, such as 120 or 480 to energize the transformer windings to keep just a small amount of heat in the tank. I only remember doing this for spare transformers that would be in storage on a pad for indefinite periods of time. It would be somewhat of a safety problem and operational headache to do it on a unit that is being used occasionally.

I think I would discuss it with the transformer supplier and see what their recommendations are. There are hundreds of these units out there now with the same problem.

I agree with BJC that cycling the transformers during the cold months would probably be worse than just leaving them off.

 

[MarkAthay]

Any method of heating a transformer will take energy, and you might be better off keeping them energized. Insulating them will allow you to reduce the energy required, and thus using some other method besideskeeping them energized.

I have seen substation transformers de-energized during the winter that used a nitrogen blanket and not a conservator tank like yours.

If you were intent on de-energizing them, I'd let them cool off while monitoring the oil level in the tank, watching it so it doesn't get too low and cause you problems. You may have to add oil in the fall, and drain it off in the spring as they warm up.

Mark in Utah

 

I have, in the past connected 120 v ac to the HT side of power transformers, as jwerthman (Electrical)also mentioned, and shorted the LT side of the transformer. This helped in generating almost enough heat for protecting the transformers from very low oil levels and leaks.

May be this helps.

elect

 

[stevenal]

Almost? Anyone for horseshoes?

 

[incline45]

We have operated spares cold for years. There is some risk so you have to look at the cost/benefit. The savings in losses really add up. For large GSU I would add nitro blankets to your tanks justified based on the loss savings Watch for water and test before energizing.