Wiring phase converters in parallel and tuning?

[userbronco]

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.

 

[OperaHouse]

If I understand what you are saying, that current doesn't seem odd at all. The compressor motor acts as an additional phase converter in parallel so it will draw additional current on one phase. If more power is needed another 3 phase motor can be added. Start converter, then motor, then compressor.

 

[userbronco]

The problem is the compressor has a current sensor that is factory set to trip at 45 amps.

Runs fine on the 3 phase from the power company, draws almost the same amps on all 3 legs, but not on the juice from the RPC.

 

[waross]

Trial and error. Try adding more capacitors and see if it makes a difference.
If we knew the line to line voltages on the compressor motor when it is running it may help with an answer. 119,117 doesn't tell us much about a three phase motor.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[OperaHouse]

One leg from the RPC is ALWAYS goung to draw more current. The phases will never be balanced from a RPC and the compressor motor will try to rebalance drawing more current on one leg. An additional free running motor in parallel may get it down enough not to trip.