In the course of increasing electric mobility, the effect of electricity on parts of machines is more significant than before. Rolling bearings and their lubrication, as a part of electric motors, are subjected to harmful currents, which lead to damage in the bearing in the long term. In order to avoid such damage, the influence of the lubricant in the bearing is becoming increasingly important. The electrical behaviour of the system can be investigated by analysing the discharge currents and the breakdown voltage in rolling bearings with lubricants of different compositions. This paper presents a procedure for characterizing the breakdown voltage at the rolling bearing and the influence of conductivity of the lubricants on harmful electrical phenomena.

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.