stepping up 220 3phase to 380/440 with cycle question

Hi All,

I'd love some help getting an English lathe (a Britan repetition) up and running. My shop has 220v 3 phase power. The electrical information on the machine tool says 380/440 volts 50 cycles 4-8 amps. The machine has a high and low speed, hence the two different amp draws. My power is 60 cycles. I believe that a VFD could make the change in cycles but I don't know if I really need to do that. It is expensive and I still would need to step up the voltage. There are no electronic components and I found a transformer on eBay that is: 7.5 KVA 3 phase primary 200/230 volts and secondary 346/415 50/60 hertz.
Could I run the lathe on this transformer? Would it hurt the motor or leave it underpowered. Perhaps I could take the motor in for rewinding to allow it to run on 220 v, but I'm afraid that I need the higher voltage to keep the motor's compact size. I'm sorry that all this is way beyond my knowledge base so I really appreciate any help you can offer. Many thanks,
David

Most motors have a frame size which is a function of the highest rated horsepower and the lowest rpm at "base speed". A higher or lower voltage does not change this.

For a single-voltage motor, a higher voltage will employ more turns of thinner magnet wire, just as a lower voltage will employ less turns of thicker magnet wire. In both cases, the "slot space" is about the same.

Most motors have 36 slots, and the three phases are spread across those slots in three groups of 12. For single-phase motors, the two phases are spread across two groups of 18 (assuming a capacitor start/capacitor run motor, which is really a special case of a two-phase motor).

AC motor design and performance is based on a ratio of votage and frequency. As long as you maintain that ratio +- 10% you are fine. So if your motor is designed for 380V 50Hz, then the V/Hz ratio is 7.6:1 and if you multiply 7.6 x 60Hz, you get 456V. If you use that special transformer and give the motor only 415V at 60Hz, you are going to be starving it for voltage. 415/60 = 6.92V/Hz. It might still be within that 10% range, but it's right on the ragged edge so your motor will run hot and produce less torque, so it will more easily overload. So just get a standard 240-480V transfromer off the shelf somewhere and it will work fine.

You motor will however spin 20% faster (60/50) and since it will put out the same amount of torque, = tq at higher speed mean more HP, but that's somewhat irrelevant, it's usually the torque you are after.

And by the way, 7-1/2 kVA should be the right size.

Thank you both for the valuable advise. I really appreciate it.