Calculation of roller and ball bearing capacitances and prediction of EDM currents

The paper deals with the calculation of the roller and ball bearing capacitances by analytical and finite element methods 2D and 3D. The central lubricant thickness and the contact Hertz´ian area are calculated using the EHD theory. Two equivalent circuits are tested for EDM current prediction in big induction motors, one which uses the measured bearing voltage and another, which uses the measured line-to-earth voltage. The results are compared with measurements. A method to evaluate the bearing resistance by measurements after breakdown is proposed.