Maintaining the environment of the motor is as important as maintaining the motor itself. For example, as voltage imbalance increases past 2%, you get dramatically more heat in the motor windings. Excess heat stresses the winding insulation. If this condition persists, the insulation will fail. The result may be a phase-to-phase short (a motor running with this condition is said to be “single phasing” because only one phase remains “healthy”) or a phase-to-ground short.
A phase monitor on the supply will alert you to this sort of fault, but you still have a damaged motor. Power monitoring on the supply can alert you when voltage imbalance is greater than 2%. However, if you perform periodic thermographic analysis on your critical motors, you can quickly identify an overheating condition. If your motor PMs are good, you know to look for environmental problems such as voltage imbalance, harmonics, waveform distortion, load issues, ventilation problems, and contaminants.