Harmonic Distortion Symptoms - Motors

Motors are sensitive to voltage distortion. In essence, when a distorted voltage excites a motor, higher frequencies are being injected into the stator. This creates harmonic currents in the windings that, in turn, can lead to several problems.

  • First, higher frequency currents cause higher operating temperatures in the windings due to eddy-current losses. These higher temperatures are not dependent on the RMS current level, so motors will overheat even though they're not fully loaded.
  • Second, harmonic voltages can produce excessive vibration in both single and three-phase motors. Vibration leads to higher than normal wear and tear on bearings, and can even impact motor shaft reliability.

Variable speed motors are gaining in popularity. Normally, the electronic drive controller and the motor are in the same package from the same vendor. However, if the drive is a separate device added to an existing motor, then the quality of the voltage from the drive feeding the motor should be examined.

Also, keep in mind that variable speed controllers are electronic devices. They're naturally susceptible to power quality disturbances, and they create current distortion. Introducing more current distortion into a power system may make other loads and the distribution system itself subject to even more problems.