Characterization of Electroerosion Damage at Early Stages Induced by Bearing Currents in Variable-Frequency Motor Bearings

Bearing current-induced damage is a critical issue in high-power variable-frequency motors, leading to electroerosion craters on bearing raceways and balls due to discharge events. This article presents an innovative early-stage model for electric corrosion crater damage in motor bearings, which quantifies the damage caused by bearing current. By analyzing discharge energy using a modified electric discharge machining (EDM) heat source model, we calculate the dimensions of corrosion craters and investigate the effects of load and speed on the shaft voltage, bearing current, and electroerosion crater size. Experiments conducted with discharge voltages (3, 6, and 9 V) on a CNC machine demonstrate that crater depth and width increase with higher voltages. The outer ring raceway shows larger craters than the outer ring ball, while the inner ring ball reveals larger craters than the inner ring raceway. Material melting and crater formation are most pronounced on the outer ring raceway, displaying significant dimensional variations across components. These findings enhance the understanding of bearing current damage mechanisms, assisting in the prediction and prevention of failures in motor systems.