Measuring of electrical currents, voltage and resistance of an axial bearing

Bearing currents induced in electrical motors driven with fast switching power electronic inverters lead to bearing surface damages on the raceway. This may be the case especially when the rotor is electrically connected to the earth potential of the system e.g. via the cogging wheels of a coupled gear. In this paper an axial bearing type 51208 is investigated at standstill and in rotation concerning the bearing resistance. The a-spot situations are estimated in standstill based on the measured signals. In rotation the bearing resistance is measured for a range of operating speeds from 0 rpm to 3000 rpm, a range of bearing currents from 0.5 A to 3 A, and two axial forces 180 N (rated condition), 800 N. A special test rig is designed to measure the bearing voltage and current signals without using mechanical brushes in the rotating system to eliminate the contact resistance of the brushes in the measured bearing signals. The results allow to predict the bearing electrical behavior at a bearing current flow through the ground.