unbalanced 3phase
unbalanced 3phase
(OP)
Is it possible for an unbalanced 3 phase power supply to damage a properly rated starter/overload? What exactly is the problem that may be caused by an unbalanced power supply?
I have a problem with the supply voltage not only being more than 10% out of the 230 +/- 10% rule but with varying voltages with a range of approx. 30v ph-ph. Apparently an overload is failing on one leg......
any information would help....
THanks,
Mark
I have a problem with the supply voltage not only being more than 10% out of the 230 +/- 10% rule but with varying voltages with a range of approx. 30v ph-ph. Apparently an overload is failing on one leg......
any information would help....
THanks,
Mark






RE: unbalanced 3phase
A 10% voltage imbalance is severe and your motor will draw very imbalanced current. It's possible the unequal current is high enough on one leg to damage the starter/overload, but that seems unlikely. Generally, the motor would fail before the starter.
But the "+/- 10% rule" you mention relates to the voltage level, not the imbalance. If your voltage is 10% low uniformly on all three phases, that will also cause high current flow to the motor.
To determine voltage imbalance, take the average of the three voltages and compare with the phase voltage that is furthest from the average (either above or below). This percentage is the voltage imbalance. It should not exceed about 3%.
RE: unbalanced 3phase
RE: unbalanced 3phase
They are using a phase adder to a single phase supply then feeding the contactor/overload - motor circuit with that. It appears that they've measured various voltages on each leg (ex: 256,240,273)
RE: unbalanced 3phase
RE: unbalanced 3phase
With those three voltage values, your imbalance is about 6.5% if my math is correct. That's bad. The current imbalance may be 30 to 40%. This can be checked with a clamp-on ammeter. If this is a motor you care about, and it normally operates close to its rating, I'd be concerned.
RE: unbalanced 3phase
RE: unbalanced 3phase
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