Re: Current and voltage unbalance
Bob,
Current unbalance generally indicates a problem with the windings of the motor. Voltage unbalance usually indicates a problem from the feed of the motor, such as a transformer that is failing. The relationship can be related, but generally I have seen them as separate issues in an industrial environment (my knowledge and experience is limited however!)
The motor life can be affected greatly over time, if not ending the motor's life immediately, if the unbalance is large enough. Very small motors can be affected with small current unbalance, as large motors can tolerate small current unbalance. Even a 60hP motor will only tolerate a few amps (10A or so) imbalance w/o affecting its' lefe expectancy over time.
Efficiency will be affected by current and/or voltage unbalance as well. If an unbalance occurs, more heat (I2R) losses will be induced on one winding vs. another. These winding losses will create an induced field, which in turn will lower the efficiency of the motor. Motors are by nature inductive loads anyway, so the addition of an unbalanced circuit on an already inductive load will only create more losses.
Hope my opinion helps.
Frank Brown