Transformer No-load losses 1

[kurti]

I'm told that I can save energy by isolating transformers that are not being used, however they are still energized. I understand that the no load losses can be anywhere from 0.0025 times to 0.0001 times nameplate rating. So a 1000 kVAR transformer is still consuming 2.5 to 0.1 kW. I would like to have a better number than the range I have listed.

 

[jghrist]

No-load losses will vary widely. Best thing is to get factory tests for a sampling of the transformer in question. Your transformer manufacturers will probably also give you typical values. Losses will be lower if you purchase transformers on a loss-evaluated basis.

A recent bid for 5000 kVA 13.2-4.16 kV transformers had no-load losses ranging from 0.00076 to 0.00142 times nameplate. No-load losses from a study done in Egypt were 0.00175 times rated for a 1000 kVA 11-0.4 kV transformer.

 

[DanDel]

kurti, another way to look at the situation is that by keeping the transformer(s) energized, you are minimizing the degradation of the insulation by moisture which may cause a failure upon energization later on, and at the cost of only '2.5 to 0.1 kW'!

 

[jghrist]

DanDel,

I was going to suggest the same thing, but then thought about how many distribution transformers utilities keep in stock unenergized. They wouldn't think of energizing all the spare transformers in the storeyard. Large power transformers, yes, but not a 1000 kVA distribution transformer.

 

[DanDel]

jghrist, don't forget, utilities don't usually test and/or maintain their transformers, they just replace them(with one of those spares)when they blow up.
This is economical for them, because they have a lot of spares, and when a piece of equipment fails, it's not their lights that go out.