Calculation and validation of a bearing impedance model for ball bearings and the influence on EDM-currents

This paper deals with the electric bearing impedance model for a ball bearing, based on a detailed mechanical bearing calculation. Based on the model, it is shown, how electrical parameters as well as mechanical parameters have an effect. The influences of the electrical and mechanical parameters are presented for EDM-currents Electrical Discharge Machining currents (EDM) at PWM voltage source inverter operation. For the calculation of the bearing impedance and description of EDM currents the electric properties of the lubricant, like dielectric constant, specific resistance and dielectric strength are discussed. The mechanical parameters such as bearing load, Hertzian area and lubrication thickness are necessary to be calculated. Calculated and measured bearing impedance are presented. A method to predict the speed range with EDM-current occurrence is discussed for the bearing type 6205 C3 and a mineral oil based lubricant.