This paper presents a practical approach to eliminating
both bearing current and ground leakage current from
an inverter-driven motor rated at 400 V and 3.7 kW. When
the shaft voltage with respect to the motor frame exceeds the
dielectric breakdown voltage of thin lubricating grease films in
two metal bearings at the drive and non-drive ends, an electrical
discharge machining (EDM) current flows through the bearings.
A passive electromagnetic interference (EMI) filter can keep the
shaft voltage in check, as a result of having eliminated high-frequency
common-mode voltage from the motor terminals. Hence,
no dielectric breakdown occurs in the grease films, so that no
EDM current flows in the bearings. Experimental results verify
the viability and effectiveness of the passive EMI filter designed in
this paper.
