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3-Phase Transformers in Parallel?

I have two currently unused 3-Phase transformers, one 30KVA and the other 45 KVA. Both are connected in reverse, converting 208 up to 460

I need 65 KVA of 3-Phase 460 power to run a new motor (50 HP)

I cannot connect just one transformer as I don't have a panel that will accept a large enough breaker to power it.

Can I connect the two in parallel if I match their output voltages within a couple of volts?

If so, would I just take the outputs from each transformer, make sure the phasing is the same, and then connect the outputs to the motor?

Thanks for any answers...

T.C.

Reply to
Tim C.
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Well, in short, what you're suggesting is totally against code (for some good reasons).

From a theoretical point, besides just phasing, you need phase-rotation to match, and you need to be careful that they are both similarly connected. If one is wye-wye, and the other is wye-delta, or any other mixture,

*boom*!!!

Feeding your load with two transformer banks, fed from two circuits has a lot of other issues as well. What if one circuit breaker opens? Depending on the amount of load on the motor at the time, you may just trip the other breaker when the load current shifts to it. But it may continue to run for a while, overloading the powered xfrmr bank.

With the two circuits feeding the two xfrmr banks, how do you think the current will be shared/split between them? The internal impedance of the two xfrmrs are different, so they *may* share the load in the right proportions, but can you know for sure?

daestrom

Reply to
daestrom

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