voltage moniter and phase imbalance 1

[technodork]

I just installed a Wagner 3-phase voltage moniter on a 3-phase 480VAC fan motor and here's the rundown:

-This motor has been replaced twice due to a phase loss burning it up. So I suspected power problems.

-now it shuts off, and stays off, until the main circuit is reset.

-went to check on the voltage moniter, and it is set to a 15% voltage imbalance as its maximum tolerance, and a 10% phase imbalance as its maximum tolerance.

My question is what are the proper acceptable ranges for 480V 3 phase, at what point should I call the power company if I read 25 or so imbalance warnings on the moniter's trend log?

 

[waross]

I would first measure the voltages at the motor starter with the motor stopped and running.
I would then do the same at the main panel. This will identify the location of the problem. If the voltages at the main panel are uinbalanced call the utility. They will probablly appreciate that you have first checked out your own wiring before calling them.
They may be quite helpful. I have had the utility adjust transformer taps to compensate for chronically low voltage on one phase.
respectfully

 

[bklauba]

To address the motor burn out, due to phase loss: There are solid state overload relays that trip within seconds of detecting a loss of phase. Likely one of these are much cheaper than a fan motor (or the time to replace it!)

BK

 

[aolalde]

In America, NEMA MG1 Standard allows for 1% voltage umbalance for 100% motor power capacity and up to 5% umbalance if the motor is derated to 75% of the design power capacity. Note that the current umbalance in a three phase induction motor is 6 to 10 times the voltage unbalance.

The main problem is overheating due to negative sequence currents in the rotor winding.

 

[jraef]

The rule-of-thumb that I have often heard is that a 10% voltage imbalance will cut your motor life in half.

You appear to have a serious problem with your line voltage balance. It may not necessarily be the fault of the utility, your own facility loading may be the culprit. Rather that continuing to throw money at it to buy hardware, a prudent investment at this time may be to bring in a professional who can analyse your power quality.

JRaef.com
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