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In the last decade, the use of PWM voltage-source inverters to control three-phase squirrel-cage induction motors has increased significantly. Consequently, high-frequency current activity in the bearings of inverter-fed motors and/or of devices mechanically coupled to their shaft is presently a common issue, ultimately shortening the bearings lifetime. In fact, bearing failures occurrence in inverter-fed motors increased dramatically in the last few years. Recently, the effectiveness of insulation-based bearing current mitigation techniques (e.g., bearings with insulated rings or ceramic spheres) and/or motor shaft grounding with an electric contact brush has been fairly investigated. However, there are some alternative high-frequency common-mode bearing current mitigation techniques requiring further investigation. In this paper, a stator slot-embedded partial electrostatic shield to reduce the capacitive coupling between the stator windings and the rotor in inverter-fed motors is proposed, analyzed, and implemented, being experimentally demonstrated its practicability and effectiveness in attenuating the common-mode voltage between the rotor shaft and the frame/ground, contributing to the reduction of high-frequency common-mode bearing current activity.
Date of Publication: June 2012