Wiring three phase transformer to a rotary phase converter

I am worried about wiring a transformer to my rotary phase converter because of the high voltage to ground on the generated phase. If as in the diagram if it is Delta - Wye is there anything to worry about. Thanks in advance for any information provided.

I will have to feel it backwards (208-570) so would I have to remove the ground from Y??

If your RPC output is 240V, its not a good idea to feed a 208V transformer coil, with over voltage +15%.

If you were backfeeding a WYE winding, with your center tapped DELTA supply (wild leg), you would not connect anything to the X0 (center) terminal, it would be left floating.

The worst thing about backfeeding this unit, would be grounding of the Delta output. Your choices would be to corner ground it, or leave it ungrounded. Neither of these is a good choice.

You would be better served to find a different transformer.

Don Gitzel said:

I will have to feel it backwards (208-570) so would I have to remove the ground from Y??

Click to expand...

Tie it off, yes. There is nothing the RPC side can DO with it, any more than it can use the Utility mains neutral.

So it should WORK. But it is far from optimal.

It's a great choice for HV RPC input side outputing to a LV load side.

Wound "Delta-WYE", so it re-derives a Neutral yah can Earth at the frame of the load for a "local Neutral" and then NOT have more than 120 VAC above ground, any leg to ground.

I use an EGS-Hevi-Duty Delta-Wye at near-as-dammit "one to one" for that very purpose, 230-230 nominal, not 208, neither Voltage boost nor drop. Gives me isolation and that 'less lethal' limitation of ~ 130-odd above Earth, plus all legs the same, not one of them higher.

Your one would NOT even be on my menu for back feed, putting Delta into the Wye Windings to get Delta out.

Didn't say it wouldn't work. Just that I'd go and get a different transformer. As I did.

RPC are inherently "Delta" and NOT "Wye", so yah either want a Delta-Delta or a Delta-Wye.

Got a 15 KVA 2:1 Delta-Delta I'd be happy to be rid off, but it's an Eliptical Coil Uptegraf, waaay too heavy to affordably ship, least of all clear to Canada.

Hammond is a decent maker, and "local" up North. There will be others around.

I don’t understand how a RPC is considered a delta output. The idler motor is a 9 lead y wound motor. Quote:

If you were backfeeding a WYE winding, with your center tapped DELTA supply (wild leg), you would not connect anything to the X0 (center) terminal, it would be left floating.

Don Gitzel said:

I don’t understand how a RPC is considered a delta output.

The idler motor is a 9 lead y wound motor.

Click to expand...

Doesn't matter. The way it "converts" is to turn the pilot or "idler" motor into a rotary transformer. CEMF off the one "powered" phase, motor literally "idle" as to local shaft load, couples back, phasing now dependent on the physical arrangement of the windings and where their fields have rotated to. Three of them, no longer just one. Of course. That's why we call it "rotary" as well as "phase converter".

That's part of the process that shifts the single input phase into three phases at the output. They end-up "displaced" in a manner of speaking. Pushed sort of sideways in time away from the grid's phase position.

So their Neutrals no longer agree with the Utility mains Neutral, either. Won't much MATTER until.. yah put a 120 VAC "control" transformer any leg to "new neutral". Best to just NOT. Use a 2XX primary control instead, and place it across any two legs BUT the "generated" leg. Higher-rated primary yet, if yah feed 4XX and up.

Check the "stickies" here on PM.

Observe how the utility mains Neutral is handled, input vs load side of an RPC.

Same again for a Phase-Perfect, BTW.

Download their manual and read the part as to what is required for use with a transformer. Delta => Wye. No carry-through of utility mains Neutral, and the "new" Neutral yah "derive" off the Wye's common is not meant to be commoned-up to the Split-Phase Utility mains Neutral, either.

"Protective Earth" influence not withstanding. My one rates it's own ground-rod "nest".

Have a look at this thread and Peter explains the difference of the neutral from you 1Φ system from your 3Φ output, which has no neutral connection from your idler windings.

Thread: Three-Phase vs. Single-Phase, Illustrated

SAF Ω

Dont mean to sidetrack this thread but I have a question related to all this. Wondering if anyone can confirm the proper procedure on how you connect the WYE center point on the secondary of an isolation transformer used with a phase converter. The X0 terminal in the attached picture. This is connected to ground to eliminate the high leg problem right? Is ground wire ok or should there be a separate neutral wire all the way to single phase panel? Or something else?

I bought my phase converter used, it came with an isolation transformer and I had an electrician friend hook it up. Its been working fine for 3-4 years but he was a little uncertain about this part, and im not sure X0 is hooked up properly or even if its connected to anything at all.

Also both my CNC's have their own transformer for high/low voltage. Since they have their own transformer anyway, does this mean I didn't really need to use the isolation transformer at all?

https://www.kijiji.ca/v-other-busin...p_ios&utm_medium=social&utm_source=ios_social

Could this auto transformer be wired to a RFC as a step up or step down transformer??

Don Gitzel said:

https://www.kijiji.ca/v-other-busin...p_ios&utm_medium=social&utm_source=ios_social

Could this auto transformer be wired to a RFC as a step up or step down transformer??

Click to expand...

Probably. So could the first one you asked about.

But it isn't an improvement, may even be a WORSE choice.

Start with clearly defining the need. THEN look for the goods to satisfy that need.

Not the other way 'round.

"As far as we can tell".... You have a 230/240 VAC single-phase feed to an RPC and want to boost the 3-P output to 575 VAC 3-P?

Confirm that you have that. please?

AND... are NOT willing or not able to simply re-strap the load for the lower Voltage.

At which happy point you would not need ANY boost transformer - nor even "600 Volt Class" switchgear, wire, protective devices, and related goods.

"As far as we can tell".... You have a 230/240 VAC single-phase feed to an RPC and want to boost the 3-P output to 575 VAC 3-P?“
Yes, this is the case. When you say re-strap the load for the lower voltage do you mean change out the motor and controls to the lower voltage. What if the motor is flange mounted. Gets more complicated. Cheers!!

Don Gitzel said:

"As far as we can tell".... You have a 230/240 VAC single-phase feed to an RPC and want to boost the 3-P output to 575 VAC 3-P?“
Yes, this is the case. When you say re-strap the load for the lower voltage do you mean change out the motor and controls to the lower voltage. What if the motor is flange mounted. Gets more complicated. Cheers!!

Click to expand...

Nothing to do with altering the motor "physically". Only "electrically".

Many, if not most (100%, here..) machine-tool motors can be re-connected to run off either 2XX or 4XX. It's just some wires to group differently in the peckerhead, the diagram for it right on the motor's dataplate.

No big deal, that part.

As expected current will have roughly doubled (or halved), one needs to also swap a "heater" or over-current protective device, usually at the "Motor Starter" contactor's box.

Or bypass it and provided separate fuse or common-trip circuit-breaker "inline" if a proper fit is too hard to source.

Flange-mount motors are standard items, too. All manner of 'em. That need not be a big deal, either.

Great information. Thanks.

240V to 600V RPC RPC

Don, you may want to have a look at this thread. A RPC built to produce 575V with a 1Φ transformer on the front end, instead of a a 3Φ one on the rear end. The required parts may be easier to source for you. But please be careful, 600V is not forgiving to amateurs or anyone else, for that matter. Most of the 600V motors I have come across are made for a single voltage, so reconnecting them for a lower voltage may not be possible. You want to check the other control components in your controls as well, as many will likely need to be replaced to run at a lower voltage.
Do your home work first, it's cheaper and easier that way.

A 240V Delta to 600V Wye 3Φ transformer used, would be a rare item in your area I would suspect, and expensive for a new one. Hence is why I suggest you look at this other method. It was successfully built and run by a electrical greenhorn member here.
jappietoutou from Quebec

https://www.practicalmachinist.com/vb/transformers-phase-converters-and-vfd/240-v-575-v-3-phase-converter-project-314554/?highlight=600V+RPC

SAF Ω

mmurray70 said:

Dont mean to sidetrack this thread but I have a question related to all this. Wondering if anyone can confirm the proper procedure on how you connect the WYE center point on the secondary of an isolation transformer used with a phase converter. The X0 terminal in the attached picture. This is connected to ground to eliminate the high leg problem right? Is ground wire ok or should there be a separate neutral wire all the way to single phase panel? Or something else?

I bought my phase converter used, it came with an isolation transformer and I had an electrician friend hook it up. Its been working fine for 3-4 years but he was a little uncertain about this part, and im not sure X0 is hooked up properly or even if its connected to anything at all.

Also both my CNC's have their own transformer for high/low voltage. Since they have their own transformer anyway, does this mean I didn't really need to use the isolation transformer at all?

Click to expand...

Instead of cluttering up Don's thread, please start your own. Include a complete picture of your transformer label, and state the voltage you are feeding it, and what the voltage requirement are of your load equipment. The onboard equipment transformers labels would be helpful as well, so that you don't get the wrong advise, with assumptions.

SAF Ω