Unbalanced open delta loads

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zbang said:
Hmm, maybe take the motor out of the equation-
find yourself three 8kw 240v heaters, wire them in delta, and connect to the motor disconnect. When that's energized, if you don't get even current readings, there's a problem either in you premises wiring or in the service itself. Take voltage and current readings up the line until you get to the service disconnect should lead to the problem. Or even move the dummy load from the motor disconnect to another 3-phase breaker somewhere else in the system.

If the issue continues all the way up to the service disconnect, call the PoCo back.

Get lots of voltage (L-L, L-N, and L-G) and current readings, the only extra cost is your time.
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I was thinking about using an old electric range and testing one phase at a time at the service. Have to rig it so no neutral is required.
 
zbang said:
But where? The OP says the currents are all the same when on the generator.
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I think it could be at the service drop. If this is an old service, I have seen the poco use four insulated wires to insulators instead of a quadraplex, the neutral would be insulated, and if not bonded at the transformer or building service, could give the voltages the op is seeing, yet have a phase faulted to ground. The transferswitch could be a four pole. Pictures would be nice, at this point we can only speculate.
 
Joethemechanic said:
I was thinking about using an old electric range and testing one phase at a time at the service. Have to rig it so no neutral is required.
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Thanks, I bypassed everything. I took the Power comp wire off the line side of meter and jump straight to mdb in the control panel. They reinstalled the jacks and nothing changed.
 
hillbilly1 said:
I think it could be at the service drop. If this is an old service, I have seen the poco use four insulated wires to insulators instead of a quadraplex, the neutral would be insulated, and if not bonded at the transformer or building service, could give the voltages the op is seeing, yet have a phase faulted to ground. The transferswitch could be a four pole. Pictures would be nice, at this point we can only speculate.
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All new. Transfer switch is 3 pole. Everything new at pole to lift station. Neutral bonded.
 
ptonsparky said:
These are voltages while under motor load or static no load?

Are you tripping overloads? What brought this issue to your attention?
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Everything was checked both ways. Start p reports 3 years ago showed issues. Now that we sized all gen sets using VFDs the dc buss keeps faulting the drives. Sometimes during the prime time they will not reset. Dirty power what I call it.
 
kclark8799 said:
Everything was checked both ways. Start p reports 3 years ago showed issues. Now that we sized all gen sets using VFDs the dc buss keeps faulting the drives. Sometimes during the prime time they will not reset. Dirty power what I call it.
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You're using vfds on a hi leg delta? Is the 15 HP on a drive?
They're a lot of details being left out.
 
ptonsparky said:
You're using vfds on a hi leg delta? Is the 15 HP on a drive?
They're a lot of details being left out.
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I have approximately 130 VFDs on an open delta , 47 on 480 Y system and 11 more on water wells and they all work great except for this one. Really don't know what else to present. Danfos suggested talking to the power company about the grid.
 
Are there any customers on the same primary circuit that might have a large data center or maybe a bunch of 6 pulse drives? Maybe take a look at the waveform on that leg with an oscilloscope. You can get multimeters with an oscilloscope for like 100 bucks now

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Lots to choose from, all kinds of features
 
Was the VFD and the motor moved to the generator or just the motor when tested? With that many drives you should have a spare on hand. What Is the feeder? Underground? Have you megged the conductors or check the condition of all splice points. Again, where are you measuring current and voltage? Line side or load side of the drive? Does the motor operate properly ATL?
 
ptonsparky said:
Was the VFD and the motor moved to the generator or just the motor when tested? With that many drives you should have a spare on hand. What Is the feeder? Underground? Have you megged the conductors or check the condition of all splice points. Again, where are you measuring current and voltage? Line side or load side of the drive? Does the motor operate properly ATL?
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Yes VFD has been part of system. Each control panel has 2 drives both react the same.poco replaced Everything. Transformers twice. Line jacks drops, arresters and even added additional grounds. Voltage and current at T leads and at line side of main distribution block. Measuring with load and no load. ATL will work but still have 16 amps on A, 34 on B and 34 on C.
 
kclark8799 said:
... ATL will work but still have 16 amps on A, 34 on B and 34 on C.
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Are you saying that you get these unbalanced current measurements when across-the-line, as well as when feeding the motor with a VFD?

A suggestion is to put a current clamp around all of the conductors feeding the VFD (i.e., A, B, and C) to verify that you don't get a significant current reading. That's just to make sure there isn't some other current path involved. It's not likely to be a problem, but it's probably easy to check.
 
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