Transformer overload

[thinker]

When ordering a drive isolation transformer should I specifically request the overload capability 150% for 60 sec, or this overload will be provided anyway based on some general standards transformer manufacturers must follow?

 

[Skogsgurra]

There is no such thing as a "good measure" when buying transformers.

You get exactly what you specify. If you say 10 kVA - you get 10 kVA. If this is for a frequency inverter you should make sure that the bad power factor (not displacement PF but distortion PF) is taken in account.

A 50 percent overload (i.e. 150 percent load) for 60 seconds is not a problem for a reasonably sized transformer. It has a lot longer time constant - probably in the 15 minutes region, if naturally cooled. Forced cooling will make the time constant considerably lower and you may have a problem with 50%/60 secs overload. But not with a self-cooled one.

If the transformer manufacturer is any good, he will be able to help you out if you explain the application.

Gunnar Englund

http://www.gke.org

 

[thinker]

Thanks, Gunnar. I actually tried to find out whether UL listed transformers (USA) provide this overload as a default (range 200-800 kVA).