I have a building with a 1200a 480v 3p 4w. The 480 supplies power to 3 transformers for 208/120 building loads on 3 seperate breakers. It also supplies 480 3p power to a chiller panel with four commpressors on its own breaker and a pump panel with four pumps on its own breaker. All the moters are 3 phase, and the voltage is a little high a-b=498, a-c=496, b-c=488 and a-gr.=287, b-gr.=279, c-gr.=280. The problem is all moters draw more amps on a-b phase. comp. 1 69a,64a,61a. Comp.2 73a,62a,59a.The comp. tags are 81a. Pump 1 3.67a, 3.25a, 3.17a.and so on. There are 3 transformers on pole near building. One is phisicly larger but i don't know act. size. thanks, john
current imbalance
- Thread starter jociha
- Start date
- Status
- Location
- Illinois
- Occupation
- retired electrician
Re: current imbalance
Don
This seems strange for a 480 volt, 3 phase, 4 wire system. Normally only banks that supply 120/240, 3 phase, 4 wire systems use one larger transformer and one or two smaller ones. The difference in the impedances of the transformers could be the cause of the voltage and current inbalance.
Don
Re: current imbalance
The building is about 6 years old and there has not been a lot of equipment faiulure but i am told this has been there as far back as the first year, maybe since day one and the new owners would like to address this problem.Thought i would check with everyone before i call the utility co.
The building is about 6 years old and there has not been a lot of equipment faiulure but i am told this has been there as far back as the first year, maybe since day one and the new owners would like to address this problem.Thought i would check with everyone before i call the utility co.
charlie
Senior Member
- Location
- Indianapolis
Re: current imbalance
Quit checking and call the electric utility! They can check the nameplate impedances of all three transformers to verify that they match. There may also be a problem with one of the transformers or a bad connection. The physical size of the transformer has no bearing except that one is probably older or from a different manufacturer than the other two.
Quit checking and call the electric utility! They can check the nameplate impedances of all three transformers to verify that they match. There may also be a problem with one of the transformers or a bad connection. The physical size of the transformer has no bearing except that one is probably older or from a different manufacturer than the other two.
charlie
Senior Member
- Location
- Indianapolis
Re: current imbalance
Bennie, it could be a multitude of things but I think the problem is an impedance mismatch. It could be a problem with the turns, the wrong tap, unbalanced loads on the primary conductors, etc.
It may or may not show up under no-load conditions. The bottom line is that I can't answer your questions, sorry, Charlie.
I love signing my name that way.
Bennie, it could be a multitude of things but I think the problem is an impedance mismatch. It could be a problem with the turns, the wrong tap, unbalanced loads on the primary conductors, etc.
It may or may not show up under no-load conditions. The bottom line is that I can't answer your questions, sorry, Charlie.
I love signing my name that way.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: current imbalance
Charlie doesn't this sound like the utility boosting the primary to much to overcome voltage drop? had this happen once. had the same results the voltages being to high we have this problem now on house feeds as NIPSCO says there is nothing wrong to have 128-132 volts between the hot and neutral and it is causing for alot of blown bulbs. But they wont budge. Two weeks ago they had a 972 volt spike that lasted for more than 15 seconds. and did alot of damage to appliances in homes around Portage. they are telling the homeowners that it was an act of god and there not responcable but there was no storm or any weather related problems that tuesday morning. some of these people lost everything TV's, vcr's, GFCI's. the ones that had a few surge suppressors just had to reset there mains and the branch breakers of course the suppressors had to be replaced. But they held and some were even able to trip a 200 amp main.
Charlie doesn't this sound like the utility boosting the primary to much to overcome voltage drop? had this happen once. had the same results the voltages being to high we have this problem now on house feeds as NIPSCO says there is nothing wrong to have 128-132 volts between the hot and neutral and it is causing for alot of blown bulbs. But they wont budge. Two weeks ago they had a 972 volt spike that lasted for more than 15 seconds. and did alot of damage to appliances in homes around Portage. they are telling the homeowners that it was an act of god and there not responcable but there was no storm or any weather related problems that tuesday morning. some of these people lost everything TV's, vcr's, GFCI's. the ones that had a few surge suppressors just had to reset there mains and the branch breakers of course the suppressors had to be replaced. But they held and some were even able to trip a 200 amp main.
charlie
Senior Member
- Location
- Indianapolis
Re: current imbalance
Wayne, the voltage variations are set by the IURC, check out the IURC site for more information. This covers other rules as well and, I suspect, they would not want you to know about this document.
Wayne, the voltage variations are set by the IURC, check out the IURC site for more information. This covers other rules as well and, I suspect, they would not want you to know about this document.
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