Oil-Filled vs Dry Type Transformers

[julesm]

Is there a "rule of thumb" about which transformer size means which type? For a 1000 kVA utility xfmr (SCE), is it OK to assume that this is an oil-filled?
This is for arc flash calcs. I know the xfmr %Z, but the %X and %R are calculated differently depending on transformer type.

Thanks
Jules

 

[jim dungar]

I have never known a utility to use a dry-type transformer in a standard application.

 

[kingpb]

By size, no, until you get into the MVA ratings, but even then you can get very large custom built dry type transformers. By user, e.g. utility, maybe (as Jim pointed out). But you can also look for the cooling designation. All transformer built to IEEE standards will have one.

For oil filled, look for either the old designation OA, FA, FOA or the newer designations ONAN, ONAF, OFAF, etc.

If it's a dry type then it is going to be AA or FA, or the IEC designation of AN or AF.

 

[wirenut1980]

I've installed 1000 kva dry type transformers before, but it is non-standard. If the transformer is located inside the building, I would be willing to bet it is going to be dry type, and outside a building would more likely be oil filled (not sure if you know that info).