Experimental discussions on a shaft end-to-end voltage appearing in an inverter-driven motor

This paper addresses shaft end-to-end and shaft-to-frame voltages that appear in the 400-V, 15-kW induction motor driven by a voltage-source pulsewidth modulation (PWM) inverter. A shaft-to-frame voltage can be observed at either shaft end with respect to the grounded motor frame. A shaft end-to-end voltage can be observed as a voltage difference between the shaft-to-frame voltage at the drive end (DE) and that at the nondrive end (NDE). Experimental waveforms lead to the following interesting observations: motor internal coupling and parasitic capacitance, along with the high-frequency common-mode voltage generated by the PWM inverter, cause a shaft-to-frame voltage with a peak of 8 V at both DE and NDE. When the shaft-to-frame voltage at either DE or NDE exceeds a dielectric breakdown voltage of thin bearing lubricating grease films, a shaft end-to-end voltage with a peak of 2 V and a width of 30 ns occurs along the motor shaft. This paper makes experimental discussions on the shaft end-to-end voltage generation. Installing a differential-mode filter and/or a common-mode filter on the motor drive system gives a hint on the mechanisms of the occurrence of the shaft end-to-end voltage. Index Terms--Bearing current, electromagnetic interference (EMI), ground leakage current, motor drives, pulsewidth modulation (PWM) inverters, shaft voltage.