Calculation of bearing and common-mode voltages for the prediction of bearing failures caused by EDM currents

The paper deals with the calculation of the common-mode (CM) voltage and the electrostatic induced voltage across the bearings in the small power inverter-fed AC machines with wound round wire windings. A method for the calculation of the bearing voltage directly from the CM voltage at the neutral point has been previously proposed in the literature. In this paper, a new representation of the stator winding, which is verified experimentally, is proposed to be easily implemented in a simulation software tool for the calculation of the CM voltage. Moreover, an accurate calculation of the bearing voltage from the integral of the CM current, via the bearing voltage ratio, is proposed. The EDM currents and the bearing threshold voltages, which are responsible for the occurrence of the fusion craters, electrical pitting or fluting of the lubricated bearing surfaces, are also calculated.