Phase Converter, breaker sizing. Again

In the process of buying a new machine. 2004 Daewoo Puma 300LC. It bigger than what I was looking for but it was a good deal, and local. ( and bigger is better, right haha ) The problem is I need more power for it than I have available. I only have 125amps to the shop. ( single phase ) I already have a 10hp VMC running on a 25hp converter. So I am having to have new service put in, dedicated to shop only. ( shop is now running off my home service ).

Tha machine is 44kva. 220v. FLA is 116a. So it looks like to me I need 1.73x 116a= 200A? And a 60hp converter? Geez I hope I am missing something. Seems like an awful lot but it is a good size machine.

Do these numbers sound right?

Looks like your on the right track.

44KVA @ 240V 1Φ = 183A, you may need to reduce the voltage to the machine to stay within its requirements, by using a transformer before or after your converter. You want to use the supply voltage in your calculations, for determining a feeder size. The machine voltage is only used after conversion and voltage adjustment.

SAF Ω

SAF said:

Looks like your on the right track.

44KVA @ 240V 1Φ = 183A, you may need to reduce the voltage to the machine to stay within its requirements, by using a transformer before or after your converter. You want to use the supply voltage in your calculations, for determining a feeder size. The machine voltage is only used after conversion and voltage adjustment.

SAF Ω

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Thanks, I will probably use a buck/boost to drop it before the converter like I did for the mill. Just seems like a lot of amperage, but I guess thats how it is when running 3 phase on single phase power. I know conventional wisdom is to double converter size but is it REALLY necessary? A 60hp motor ( for the converter ) is a BIG motor.

You will probably have other loads, so the supply to the shop needs to handle the machine load plus the other loads. Give yourself some margin to cover lighting, the shop coffee maker, incidental bench loads, etc. And any other machine loads that may run at the same time.

Speaking of breakers, how did you plan to wire it?

many folks have the wires to the converter also carry the load current. That means the wires to the converter must be protected at the sum of converter current plus load current. That is going to be too high to protect the converter itself properly. (Actually, at your size of converter, the converter should have its own "motor starter" with overload, etc. So this may not be an issue)

A better way to wire it is to have a separate single phase breaker and supply to the converter, sized per the specs for the converter, and then have a 3 phase breaker box which carries the 2 input wires plus the generated output leg from the converter.

That way the converter breaker can be sized properly for it, and the load breaker can be sized for the load.