Building RPC. I have 220V SP to go to a 460v 3Ph Motor back to 220v 3ph output. HELP!

[dmartin.dlm]

So I was able to pick up a brand new 15hp 3phase motor for free. I need to make an RPC and thought this motor would be perfect. Except I didn’t realize it was 460v…
What I’m wondering is if I can use a transformer to step up my 230v single phase to power 2 legs of the motor, use the motor to generate my 3rd leg , balance everything and then use a transformer to step the 460v back down to 230v 3phase output.
This is mostly bc 1: this is a new motor
2: I’ve had a hard time finding a 15hp or higher motor for under $1,000. Unless I go to a scrap yard but I can’t always text them there. The yard I found with a bunch of motors won’t let you bring tools back.

I know I have the skill set to build my own regular RPC but with adding transformers, I’m not sure what other considerations I will need when building it. Like will I need different capacitors ?
Thanks for any help
Daniel

 

[Overland]

Are you sure it's not a dual voltage motor ?
Check nameplate; pull off connection box cover - if there's 9 wires it's probably dual voltage.
Bob

 

[Almost Retired]

the motor tag will show 230V/460V if it is dual voltage
it will also show two values for FLA

you could place the caps on the low side of the transformer
or you could use a buck boost transformer on the low side of the transformer
you need one that is about 12V to 16V boost
connect it from one normal leg to the wild leg

the boost txr is much more stable with changing loads
caps need to be readjusted with large load changes
they also require checking and occasionally replacement after a few years
the booster is maintenance free

 

[dmartin.dlm]

The nameplate says 460v only but I’ll look under the plate where the wires are connected later today.
Do y’all know if the transformers I would need are expensive?
And some specifics of the transformers. I don’t know much about them but I’m very careful when working with electricity.

 

[johansen]

You can use two, 120:120v isolation transformers to boost your 240v line to 480Vac. They will need to be rated for the amps you expect to pull out of the 3rd generated leg of the rpc, plus 50% minimum. For a 15hp rpc you would be looking at two, 3kw 120:120 isolation transformers. This is probably the cheapest route and will require thermal overloads selected so you dont burn them up. Look for 5kw transformers.

so now you have 460 that is symmetrical, 240v above and below ground.

the generated leg of the motor will be 420 volts to ground/neutral.

you need to cut that in half. I recommend at a minimum a 3kw 240v isolation transformer. It gets connected as an auto transformer from the neutral of your 120/240v system, to the generated leg of the motor.

What I've described is the lowest cost method.

If you instead use a single phase 240v to 480v transformer, your motor is now isolated and has to be grounded somehow.

Then you have to find a 3 phase 480v to 240v transformer to run your loads, which are also now isolated and have to be grounded. This isnt a problem if you can find a 480 to 240v Y transformer, but those are rare. You can find a 480 to 208Y, but now you have 208. You may be stuck with corner grounding the 480v motor, this stresses the wires more.

The kilograms of transformers needed to do it this way, are 4 times more than the method i first described. However, if the transformers are free, its the way most folks would do it.

The isolation transformer method does not require grounding the 480v system, because the transformers are all auto transformer connected.

Capacitors need to be at the 480v motor, so the transformers do not need to pass the idle current drawn by the motor, 90% of which is canceled out by the capacitors.

Grounding the 480v motor if you go the usual transformer route can be achieved id you find a 480y to 240 delta transformer. Such a tx might be advertised as 480/277-240. You then ground the y point of the 480/277 transformer.

Or dont ground it and make sure warning labels are displayed if you ever hire someone else to work on it

 

[Overland]

You may end up with a lot of money in transformers and a lot of complexity in your system.
If your new motor is not dual voltage, you maybe better off selling your motor, then getting a 15 or 20 hp motor off ebay.
I picked up a new Baldor 15 hp from an auction for my RPC, for $400.
Put your location on your profile, always helps people to help you.
Bob

WEG CC029A 15 HP 575 Volts 3535 RPM 2p 213/5t Frame 3/60 AC Motor for sale online | eBay

Find many great new & used options and get the best deals for WEG CC029A 15 HP 575 Volts 3535 RPM 2p 213/5t Frame 3/60 AC Motor at the best online prices at eBay! Free shipping for many products!

www.ebay.com

 

[DDoug]

The easiest and lowest cost is ditch the "Free" motor, and simply BUY a correct motor, and forget any xformers.

 

[Almost Retired]

The easiest and lowest cost is ditch the "Free" motor, and simply BUY a correct motor, and forget any xformers.

actually he should sell the 460 to help pay for the 230

 

[dmartin.dlm]

Thank you Very much. And thank you for your detailed response Johansen.
And thank you guys. I appreciate it. And I think I’m going to go the route of buying a new one. I’ll add my location too. And I’m guessing y’all didn’t have your motors shipped from an eBay auction?

 

[Overland]

This one might be ideal. You may need to figure out how to mount it, otherwise should be excellent.
Bob

15HP 3525 RPM 230/460 VAC 3Ph Baldor Motor 37K245X895G1 | 3 Phase Motors Base Mount | AC 3 Phase Motors | Electric Motors | www.surpluscenter.com

15HP 3525 RPM 230/460 VAC 3Ph Baldor Motor 37K245X895G1, 3 Phase Motors Base Mount, 15 HP 3525 RPM THREE PHASE MOTOR New, Baldor three phaseBaldor,37K245X895G1,

www.surpluscenter.com

 

[dalmatiangirl61]

And I’m guessing y’all didn’t have your motors shipped from an eBay auction?

Shipping is high these days, crazy high if you want liftgate service to a residential address. You should shop on ebay for something close enough that you can pick it up.