how much is too much

[ZapCzar]

The call was on a 20HP submersible water well pump. Pump keeps tripping 100amp breaker. Pump Company blames this on voltage. Phase to phase no load 244v 244v 232v. This is 120/240 3phase, we serve with open wye open delta, 2 25kva transformers. The 3 phase is not unbalanced causing the wye to collapse. After moving one primary phase and switching the secondary leads to maintain rotation I was able to get the unloaded voltage to 240v 245v 250v, under load 40 amps 40 amps 50 amps 241v 243v 233v. The pump would run and did not kick off for the 10 minutes or so I let it run. My question is, the 233v under load too big a difference or just normal under an open wye configuration? If this is ok at what percent difference is it not. And before anybody says it, yes I know it’s better to have full 3 phase on water wells, but they don’t let me control the budget. Thanks for any help .

[Electriceel]

I would try replacing the 100 amp breaker sounds to me like it is getting weak and will not carry the amperage.
Submersible pump motors are a real problem, we had one on a well the contractor actually had messed up and excuse me if I use the wrong terminology, but they had to many bowls on I believe, pulled the well and removed one, have not had any trouble since.
Don't care what power provider it is, the 3 phase primary voltages are never the same, I would not worry about the voltage until it drops more than the allowed 5%.

[Pootnaigle]

I bleve your amperage readings under load if I understand correctly was 40 40 and 50. That is the key to your problem. This is a delta connection and load should be balanced. My guess is you have a motor problem.

[ZapCzar]

Thanks for the replies guys. I feel that probable ether one of you or maybe both of you are correct. A problem down in the well, motor going bad , partial ground in cable that may be changing as water level changes, and or weak breaker from constantly tripping it out. We put a PMI recorder on it just to make sure that the wye primary is not collapsing when we are not there. You know how it is, it’s harder to prove to the customer that you don’t have a problem, than it is to fix a real one.

[johnbellamy]

Put a ampmeter on the loadside of the 100 amp breaker, see what it trips at, what size are the fuses at the pump disconnect? They are not blowing?

Is this 100 amp breaker the main disconnect? aren't you drawing 130 amps total?

[ZapCzar]

This is a 3 phase breaker on the panel. There using this breaker instead of fuses. It would be 100amps per leg so no it’s not overloaded. The PMI recorder will give us a good look when the breaker trips. We will let it run a few days then I’ll let ya’ll know what it says.

[ZapCzar]

. The recorder did show an imbalance on voltage and current, but the breaker is not tripping anymore. From what I can find out there will always be an imbalance some time a lot on open wye banks. Depends alot on how balanced your 3 phase is. I can not find at what percent it is unacceptable. It seems to be voltage imbalance times customer whine equals changing bank to full three phase

[Electriceel]

Can you get a clamp around all 3 phases at the same time check for imbalance, then check for amps on the neutral. If all this looks good, get a megger and prove to the customer he has a motor problem coming up sooner or later.

[ZapCzar]

The PMI recorder gave us a good picture of current and voltage over a 2 week period. There is a lot of imbalance that could be corrected with closing the bank, but the breaker has quit tripping and we are still busy catching up on regular work after Ike. Right now the customer has quit calling , if they start again we will close bank so we dont have to mess with it any more. I think you were right about the breaker being weak, even tho there was an imbalance it was under 5% and the motor should have run fine.

[Trojan]

"There is a lot of imbalance that could be corrected with closing the bank, but the breaker has quit tripping...."
Come across a couple trouble jobs with 3 pahse motorts connected to open delta 120/240V transformers. The motor would draw too much and trip breaker. Found at two of them that motor had a starter coil that by dumb luck was fed by phantom phase of open delta. On motor start up, in rush would cause voltage collapse on phantom phase. We swapped secondary phases and kept rotation to customer (old fashioned three wire straight 240V service with no neutral). I'm pretty sure that did the trick.