rotary phase converter star up issues

I have put the finishing touches on my home built 10hp RPC. I am using a Artco 90-66 potential relay to control a contactor with a 240 volt coil for the start circuit. I have the generated phase hooked to terminal 5 on the relay, L2 of the incoming single phase power is hooked to terminal 2 and terminal 1 is hooked to the coil on the start contactor. My idler is 10hp dual voltage, 9 lead, internal wye connected motor wired for 240 volt operation. I am using 1044 uF (approx 100 uF per hp) for my start capacitors. There are six of them divided into 3 groups of 2. Each group is connected to one pole the start contactor and the other side of the contactor has all 3 poles tied together and connected to the generated phase. I do not have any balancing capacitors connected yet.

Here's what happens when I try to start the RPC. The potential relay won't open to drop out the starting circuit. The idler will run but vibrates terribly because the start circuit is still energized. I also tried to start the idler by bumping the start contactor with the main power to the idler energized. It will start but as soon as I release the start contactor the idler immediately goes to locked rotor condition.

I tried to test the potential relay by putting 240 volts across the sensing side of the relay and it did not open the contacts. I'm not sure if this is how to test it but it seemed like a good idea at the time. I suspect the relay is DOA.

I am also wondering if I need to put a flywheel on the shaft of my idler to help with the stopping of the idler after the start contactor drops out.

Sorry for the long post. Any thoughts or ideas are appreciated.

Thanks,

Eli

EliG said:

I tried to test the potential relay by putting 240 volts across the sensing side of the relay and it did not open the contacts. I'm not sure if this is how to test it but it seemed like a good idea at the time. I suspect the relay is DOA.

I am also wondering if I need to put a flywheel on the shaft of my idler to help with the stopping of the idler after the start contactor drops out.

Click to expand...

A variable transformer could be used to test the drop-in/drop-out levels of the relay. I would remove the cover and take a look. The contacts could be welded together.

A flywheel would save how many seconds? I wouldn't bother.

I'm with rons on the flywheel. Doesn't really seem necessary.

A flywheel would increase the converter's capacity for starting loads, but would lengthen its stopping time.

Thanks for the suggestions. I forgot about this thread. I did figure out what the problems were. The first one was the potential relay was defective out of the box. The second one was I had way too much start capacitance. I used 100uF per horsepower and the idler didn't like it. I took out 2 capacitors and ended up with about 660uF. I got it balanced and it works great on my 7.5hp lathe. Now if I could get the power company to upgrade my transformer on the pole.