Suppose I have two single phase transformers, call them A and B, each configured
to step down 440 to 220. Ignoring any ground connections, and
defining the primary connections as H1A, H2A, H1B, H2B and the secondary
connections as X1A, X2A, X1B, X2B, I am considering running both transformers
backwards in open delta to step up my shop-made 220 3 phase power to 440.

I drew a rough sketch: www.tinyisland.com/images/temp/xformers.pdf

If I have my 3 220 power connections labeled L1, L2, L3, and my 3 440 load connections labeled X1, X2, X3, can anyone tell me how exactly to connect these transformers in open delta?

Also, I'm wondering how much to derate the power ratings. There are two factors, one is that I'm running the transformer backwards which normally loses some efficiency; the other is that the open-delta derates the power to 57% of the total kVA, right?

Thanks!

Grant Erwin

I drew a rough sketch: www.tinyisland.com/images/temp/xformers.pdf

If I have my 3 220 power connections labeled L1, L2, L3, and my 3 440 load connections labeled X1, X2, X3, can anyone tell me how exactly to connect these transformers in open delta?

Also, I'm wondering how much to derate the power ratings. There are two factors, one is that I'm running the transformer backwards which normally loses some efficiency; the other is that the open-delta derates the power to 57% of the total kVA, right?

Thanks!

Grant Erwin

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