The standard perception of motor maintenance is that it involves work on the motor. However, this perception is incomplete. Why? Because power quality problems destroy thousands of motors each year. Motors suffer from harmonics, low voltage, voltage imbalances, and other maladies that result from poor power distribution system design and maintenance.
But why are motors special victims of power quality problems? Why do motor failure rates rise faster than failure rates of other equipment as power quality problems get worse? We can sum it up as "windings and bearings."
For example, a small voltage imbalance causes a correspondingly large temperature rise in the windings, which can bake the insulation into failure. Voltage spikes puncture the insulation material, lowering its dielectric strength until the insulation fails catastrophically.
Or consider a motor that's grounded instead of bonded. The resulting circulating currents often flow through bearings and overheat them. In cases where current doesn't flow through bearings, eventually an arc occurs between bearings and metallic objects at different potential — chewing and burning bearings to bits.