Low temp rise dry type transformers - OCPD selection

[mshields]

If you've got a 112.5kVA transformer with 115deg rise, it has an overload capability of I believe 12%. Therefore it's essentially rated for 126kVA

Assuming you will have primary and secondary protection, the primary may be up to 250% of the FLA, the secondary, up to 125%.

Should those percentages be applied to the FLA associated with 112.5kVA or 126kVA?

It seems to me that in order to use the overload capability, it would need to be the latter. Yet, there is something counterintuitive in doing so, given the nameplate kVA rating of 112.5kVA.

 

[victor.cherkashi]

I would use only 112.5kva, some manufacturers give you maximum protection size (125%, 250%). Recently I used square-d installation guide providing these numbers.

Sent from my ONEPLUS A6013 using Tapatalk

 

[ron]

For regular distribution transformers, the higher kVA rating for the lower temp rise is not on the label, so you cannot size OCPD based on it. The lower temp rise gives you longer equipment life and less HVAC needs in the room.

For larger power transformers, you will see multiple kVA ratings on the nameplate accounting for temp rise and cooling methods, then you can size based on whichever you like.

 

[mshields]

Thanks

Thanks

That makes a lot of sense