Wiring 2 rotary converters in parallel?

[roundhouse]

Hi,
Have an interesting situation.

We have a setup where we have 3 trailers with air compressors, water pumps etc, and are using 2 rotary converters, one to power a single trailer with a large load, and another converter to power 2 trailers with a smaller load.

one major load is an electric furnace, draws about 40-70 amps, another is a 25 HP motor draws about 40 amps, several various 15-20 amp loads.

The issue is, we have an air compressor that normally draws between 20-40 amps depending on the psi of the storage tank.

This compressor is drawing 45 amps on one leg and 27amps on another leg.

Ive checked the hertz,and the voltage across the legs is almost the same, at 119,117.

This compressor ran fine on the shop 3 phase supplied by the power company,so it has to be an issue with the converters.

Someone suggested that we wire the converters in parallel.

Is this common?

any tips on other troubleshooting items to check?

One converter is a new Temco ac55, and the other is an older temco (80 HP I think)


Ive called around,, but cant find anyone with experience in tuning converters, or pairing them together.

Plus company regs require any vendor on site to have OHSA 40 hr cert.

We have an electrical contractor we used before but when I mentioned "tuning a phase converter" I just got the deer in the headlights look.

Im in Atlanta, you;d think in a city of 5 million I could find someone, but Id like to learn how to do it, cause Im sure the issue will come up again.

[TarHeelTom]

Originally Posted by roundhouse Hi, Have an interesting situation. one major load is an electric furnace, draws about 40-70 amps,

Why are you running an electric furnace on a converter? I'm no expert on this, but generally speaking, most furnaces are a purely resistive load, and will run on three phase, single phase, or DC.

Granted, you could have a blower or something in there which is three phase, who knows.

Tom

[roundhouse]

Originally Posted by TarHeelTom Why are you running an electric furnace on a converter? I'm no expert on this, but generally speaking, most furnaces are a purely resistive load, and will run on three phase, single phase, or DC. Granted, you could have a blower or something in there which is three phase, who knows. Tom

The furnace does have a small blower for purging vapors before startup and it has a large blower for drawing vapor but in this site we dont need it.

I thought the resistance load may be affecting the compressor, but we shut off the furnace and it didnt change anything.

The resistance heaters are inside a catalytic oxidizer, the vapor is about 190* coming from the vacuum blower, then gets heated to 475 before it passes the catalyst.

Power company wanted $78,000 to run 3 phase 1/2 mile to the site, its a temporary job, 2 or 3 years tops.

[Al_The_Man]

I would imagine that it will run if you keep the artificial leg for each the same phase.
There is very little difference than a RPC running another motor.
Most likely start the larger one and then feed the second one direct to start it, do not use the normal start method for the second.
Now you have two motors in parallel, both acting as phase convertors.
I have never tried this but see it as a possibility.
Al.

[roundhouse]

Originally Posted by Al_The_Man I would imagine that it will run if you keep the artificial leg for each the same phase. There is very little difference than a RPC running another motor. Most likely start the larger one and then feed the second one direct to start it, do not use the normal start method for the second. Now you have two motors in parallel, both acting as phase convertors. I have never tried this but see it as a possibility. Al.

Both are regular Temco RPCs with a capacitor bank. One old with the caps in a separate box and one new with the caps in a box on top of the motor,

They both start up when the single phase is switched on. But so far up to this point we've used them wired separately,

[Al_The_Man]

They have auto start, if you can disable the auto start on the second one, that would be preferable.
The other way is to start them both and then have a 3 phase disconnect switch to parallel the three phases once they are both up to speed and the start circuit has completed, you have to make sure the disconnect couples the same three phases.
i.e. the same 240v single phase conductors and both the 3rd artificial phases.
It is only the artificial phase that is going to be different between the two.
Make sure you have everything well fused.
Al.

[roundhouse]

Like this?

Phase-A-Matic, Inc. Rotary Phase Converter Installation Instructions

[Al_The_Man]

Well there you go, you have the manufactures blessing, although the way I suggested would have been to feed both independently and once both started and up to speed THEN link them and bringing on line together.
Al.

[roundhouse]

Yeah, I think Id want to be able to use only one,there will probably be some times when I would only need one.

Right now we have a breaker for each converter, I start one, then the other, then add the loads. Furnace is first,it has to purge and reach temp before the vacuum blower in the vapor extraction trailer will kick on. The water treatment trailer has the 10 HP air compressor and a 7 HP fan and a couple of 1 HP pumps.

Ive ordered some more G-cable, soon as it comes in I will get em wired together and see about tuning.