This week we look at troubleshooting techniques and considerations when a motor is not running (de-energized), requiring controlled test signals to be sent into the motor. The fault zones related to a de-energized motor are power circuit, insulation, stator, rotor, and air gap. In less than five minutes the MCE® test can give a basic evaluation of the insulation health using resistance and capacitance-to-ground measurements, and power circuit and stator winding health using phase resistance and inductance readings. For insulation health, the PdMA default setpoints for resistance-to-ground, based on accepted industry standards, is a good place to start in determining if the insulation is acceptable for continued operation. If the resistance-to-ground is close to the limit, additional insulation tests such as a Polarization Index or Step Voltage Test may be required. For power circuit and stator health of a three- phase motor, resistance and inductance values of each phase should be nearly the same depending on the rotor influence. A comparison to baseline or last test can be critical in a troubleshooting situation, so work very hard to get a baseline test as soon as possible when the motor is running normally. Elevated phase resistance on one of the phases indicates a power circuit or high resistance connection anomaly. Reduced inductance in one phase can indicate lost or shorted turns in the stator windings. Remember that copper winding has a positive temperature coefficient, so higher temperatures means higher phase resistance. However, changing temperatures has little to no effect on inductance values.

To listen to a discussion on troubleshooting for electric motor reliability visit our PdMA YouTube Channel at https://www.youtube.com/watch?v=4ACW-AZddtQ.