Investigation of electrical contact in axial and radial ball bearings in dry and mixed lubrication states under applied AC voltages

Current flow through bearings of electrical machines may damage the bearing surface at contact points between the balls and the raceway. In this paper, the bearing electrical behavior is studied under applied AC voltages mainly in mixed lubrication state. The effect of rolling, the frequency of the applied AC voltage, the bearing force, the bearing speed, the lubrication (lubricated and not lubricated) and the type of the bearing (axial or radial) are investigated, using axial ball bearings (type 51208) and radial ball bearings (type 6205). Two special test rigs were designed to measure the bearing electrical signals without mechanical brushes.