Rotary Phase Converter Question

[Rocker4x4]

This may open a can of worms here, but I think there should be a pretty straight answer, I am putting in some machines that have three 10hp motors, (3phs). I do not have 3phs power at my place, I have to run things on phase converters (electric company quoted me $150k to get 3phs) In my other building i'm running a 40hp rotary phase converter and a transformer to get 480v to run machines in there. Now in this new building, i'm going to buy another phase converter to run these 3 motors. My question is, is there a benefit to adding a transformer to run them on 480v instead of 230v? I know by doing this it will cut the amps in half, also I can run smaller wire to the motors. But with phase converters is it energy saving using a transformer to run motors on 480v instead of 230v? If so is it worth it? Can anyone do a calculation on this per month? 8hr days roughly .10 cents a kwh..

My thought was it would be the same cost to run on 230 or 480 because electric cost is in watts. (amps x Volts = watts) so it would be the same.
230x27amps=6210watts
460x13.5amps=6210watts
I could be way wrong, so that's why i'm asking

 

[tailshaft56]

The energy usage will be about the same on 240 or 480. watts (power) = voltage X current.

example 10 amps at 240 volts = 2400 watts. 2400 watts/480 volts = 5 amps.

The 480 may be slightly more efficient do to lower losses from wire resistance but you will have losses in the transformer. someone more familiar with this than me may be able to calculate this for you. My guess is the transformer losses will more than offset any gains on 480.

 

[theoldwizard1]

If your machine has 3 - 10hp motors that run simultaneously, I don't know if residential (240V) service will be able to deliver that much power !

Can you down size to 7.5hp or better yet 5.0 hp and then switch to 240V motors and skip the rotary converter ?

 

[theoldwizard1]

My question is, is there a benefit to adding a transformer to run them on 480v instead of 234v?

There are losses associated with any transformer. Pay the cost for bigger wire, it should save you money in the long run.

 

[A_Pmech]

We have similar problems... I'm $75,000 away from three-phase power, but I have an excellent rural electric co-op. You won't save any energy running at the higher voltage. However, you will save on materials.

What you might consider doing is asking your power company if they will supply a 480V single-phase service. Mine will and it's very handy for running large motor loads. The downside being, of course, that you need dry transformer to provide 240V single-phase to your other service panels.

Make sure you talk to someone at your electric company familiar with rural grain elevator electrical if you live in farm country. They will know exactly what to do. My electric company didn't even blink at a 1,000A 480V single-phase service.

 

[rsanter]

Instead of a rotary phase converter, you can also run a motor/gen set.
This is where you run a motor and it spins another motor as a generator.
Doing this you can directly generate your own 480 3ph with no transformer

If it is a 230/480 motor I would run it 230 and not worry about it

Bob

 

[wyliesdiesels]

There is no long term savings with 480v vs 240v.

The only potential savings is in wire which isnt much. For a 10HP motor, u would use #10(28a @ 240v) instead of #12(14a @ 480v).

However, u will lose those savings with the transformer losses.

And 480v is NOT a DIY voltage.

I highly recommend that you use 240v.

The majority of folks on here do not know how to work with 480v. With one wrong move u can put yourself in a world of hurt.

If u must use 480v hire someone that knows what theyre doing.

 

[marinusdees]

As a general statement, compressors don't like phase converters. Nor do they like generators, dependent on size. I think it is the massive inrush current. Once running, they are fine. Jus' sayin".

 

[larry_g]

One other thing to consider is, Do you have to start all three motors at the same time or are they started one at a time? Do all three motors run loaded all the time or does the load travel from one to the other?

lg
no neat sig line

 

[wyliesdiesels]

As a general statement, compressors don't like phase converters. Nor do they like generators, dependent on size. I think it is the massive inrush current. Once running, they are fine. Jus' sayin".

Ive seen compressors work just fine on rotary converters...

 

[American Locomotive]

I think the problem is some compressors kick the unloader out early and have high starting currents because of it.

 

[Mr. T]

And 480v is NOT a DIY voltage.

The majority of folks on here do not know how to work with 480v.

I work on 480 the same way I work on 120; with care, knowledge, and respect.

Also, anything is DIY if you know what you're doing!

But in this situation I see no reason to run the higher voltage if it's not needed.

 

[wyliesdiesels]

I work on 480 the same way I work on 120; with care, knowledge, and respect.

Also, anything is DIY if you know what you're doing!

But in this situation I see no reason to run the higher voltage if it's not needed.

So u wear a faceshield wear gloves etc when working 120v?

 

[PCustoms]

So u wear a faceshield wear gloves etc when working 120v?

Arc flash is a hell of a way to go. There's definitely some specific protocol and risks that need to be understood. Although de-energized tends to remove all risk...

I had a close call with a compressor disconnect that had disinterested. I wisely elected to kill it with a hot stick upstream, had I pulled the switch I wouldn't be typing this.

Interesting though, when Siemens did our latest plant study some of the more dangerous areas were 240v, all due to the time curve of the breaker. None of us would have thought it until we went over the analysis with the engineer.

 

[matt_i]

So u wear a faceshield wear gloves etc when working 120v?

I really really hate the gloves. My hands immediately sweat due to the nonventilation and wet hands makes me jumpy to start. Next I feel like I'm going to drop every tool into something energized because now I have snowman hands with 2 layers of gloves, creating an issue that never would have been there.

Imo, the best safest way to work on any <600vac is to kill power, verify power is off, and then work on it.

To the O.P. I would take a look at Phase Perfect. Not cheap but its very reliable.

Also I wouldn't mess with 480v and not because of fear or danger. It makes a big difference in the wire cost if you have a giant plant with 10,000 motors in it. But even for a very large sized "residential" shop, if you have to buy the 3 pole transformer, you are never going to catch up in wire savings.

 

[Mr. T]

So u wear a faceshield wear gloves etc when working 120v?

We aren't 70E compliant. Also, I can't think of a time that I needed to work on anything energized (in fact that is very not okay where I work).

Don't get me wrong. I take 480V seriously. I just also take 120V seriously.

Edit: I work on 24VDC control circuits live all the time, but that is much, much lower risk.

 

[marinusdees]

Ive seen compressors work just fine on rotary converters...

How many, how big??