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Modern power inverters provide the industrial control industry with significant advantages. Faster switching devices have increased drive performance, but with some recently discovered disadvantages. One disadvantage, rotor shaft voltage and resulting bearing current, has become an industry concern. The oil film in a bearing acts as a capacitor and provides a charging mechanism for rotor shaft voltage buildup. Electrical breakdown of the film can damage the bearing. The paper examines the mechanical and electrical characteristics of the bearing and converts them into models. The mechanical model for the bearing contact area establishes an allowable bearing current density, which is used to estimate the effect of electrical life of a mechanical bearing. The electrical model for the bearing provides a significant advancement to aid bearing design and in the analysis of electrically induced bearing damage. Finally, the paper presents quantitative results on one solution to the shaft voltage and bearing current problem.
Busse et al. (Mon,) studied this question.