600V to 240v transformer question

Hi all, new user, long time reader here. Setting up my machine shop I have acquired a TOS SN50B lathe, powered by a 7 hp 575V 3 phase motor. Right now I am only interested in getting the machine powered up and running, I will refine the rotary phase converter I am building as I go. I have done my homework regarding RPC's, but I have a question regarding the type of transformer I need.

I purchased a 15 hp 230V 3 phase motor to be used as my idler motor for my RPC, and I intend to step up the voltage through a 600V to 240v transformer by wiring the RPC through the secondary windings. My question is, does the 240v wye secondary in the transformer cause an issue? I understand that the RPC will produce delta 3 phase power. I received a quote on a 600V to 240 delta transformer, about $300 more than the 600V to 240V wye unit. I don't know if I am overthinking this, just want to be sure I buy the correct one.

Thank you in advance for any insight, Adam.

Adam,

The ideal transformer for your use would be a Primary of 240V Delta with adjustment taps and a 600/347V Wye Secondary.

It is desirable to have a 600V Wye secondary output, for you to properly ground the output side. A delta output will result in a corner grounded system, which is not standard or desirable.

You can feed a Wye transformer primary with a delta supply, with no issue, by not connecting the X0 terminal. The problem then becomes the delta output coil. The only way to properly ground it, is by connecting one of the corners to ground.

SAF Ω

SAF, thank you for the info. Adam

Here's how (link) I solved the 240-575V problem for my Canadian Aciera F5 mill using two single-phase transformers in an open delta arrangement with a grounded corner. SAF gave me a lot of excellent advice. This setup has been totally trouble-free. I hope to ditch the RPC in favor of a PhasePerfect soon, but that won't change anything with respect to the step-up system.

Thank you rklopp

Reading through all of this again, I just wanted to add that the motor on my lathe is 575V delta, I don't know if this makes any difference to my situation.

Thanks, Adam

Aepp said:

Thank you rklopp

Reading through all of this again, I just wanted to add that the motor on my lathe is 575V delta, I don't know if this makes any difference to my situation.

Thanks, Adam

Click to expand...

I don't see how the motor being star or delta would make a difference if hooked up to my setup, as long no part of the motor's windings are grounded. I would not expect any of the motor's windings to be grounded at any point, unless something is wrong with the motor. I am pretty sure my Aciera motor is star at 575 V, FWIW.