Dry-type transformer overloading

[radug]

Hello,

I am trying to find some type of diagram or table for dry-type transformer overloading. I have found some diagrams for oil-inmersed type transformers but no luck with dry-type ones.

I need a 110 kVA dry-type transformer which will be loaded for 30 seconds max (it will be a grounding transformer). 11/0,23 kV, star-open delta with a resistance in the open delta.

As it will be loaded for 30 seconds max, I am trying to put it inside the 11 kV circuit-breaker switchgear cubicle, instead of putting it in an enclosure next to the cubicle. A 110 kVA one will not be small enough, but as it will be loaded for 30 seconds max, perhaps something as small as 25 kVA is enough.

Any experience with this?

 

[juleselec]

Check out IEEE Std C57.96 "IEEE Guide for Loading Dry-Type Distribution Transformers", particularly section 4 which has some guidance on the expected sacrifice of life expectancy due to different loading conditions.