[JohnHennessy]

I'm not sure if this would be the right forum for my problem, I have 200 amp single phase coming into the building and have a 40 HP rotary phase converter, from that it goes into a step up transformer 240 to 480 25 KVA . First question is will the rotary phase converter handle the transformer? If it can then I'm having a problem with the phase converter itself. It's powering three other 240 v three phase mills (one at a time) with no issues. The transformer was tested on power for a day before it came here... I hope some one has a simple answer... Thanks

[Eldon_Joh]

the supply you have is marginal, but if your utility or the neighbors don't have a problem with it then what's the problem?

200 amps at 240vac is only 48KW.

so i presume you have a pony start on the 40 hp rotary phase converter, and i presume you have the motor run capacitors hooked up to offset its reactive amps, which could be on the order of 30-50 amperes.

meaning, your 40hp motor sucks up on the order of 30-50 amps (almost entirely reactive) from your 200 amp "budget" and almost all of these 30-50 amps can be compensated for with capacitors, which would require on the order of 300-500uF to do so. if you're on a residential service then they don't know about this so its not a problem.. until you read in the fine print where i says something like "up to 5 or 10 hp"


anyhow yes you can just plug your 240 to 480v transformer into your induction motor phase converter, and plug your machine in. how you figure out how to ground the 480v side is up to you, and osha. and you probably want the machine controls on the utility side of your "three phase" so that it gets cleaner power that doesn't brown out when the spindle turns on.


your 25KVA transformer will suck up a few reactive vars, which will push the "generated" leg of your rpc down. you can compensate for this with delta connected capacitors across the transformer.

also, delta connected capacitors at each of your other loads. they should switch out with the loads, not remain permanently connected to the rpc.

while many people permanently connect the capacitors to the rpc, this pushes the voltage of the generated leg far too high and the motor can overheat, or the third phase is high enough voltage to trip a vfd.

[JohnHennessy]

Thank you very much, I will pass this information to someone that understands everything your saying and can help me sort all this out. I have an North America PL 40 with the control box loaded with capacitors, I dont have a pony start nor do I have delta connected capacitors at each of my loads, Something I will have to attend to.. Thanks again for you help

[JohnHennessy]

Problem solved thank you for your help