Influence of static rotor imbalance on the roller bearing damage due to inverter-induced bearing currents

The influence of static rotor imbalance on the generation of bearing fluting due to bearing currents is experimentally investigated. For that six inverter-fed induction machines with the rated power of 1.5 kW and three with the rated power of 11 kW were tested with especially prepared bearings. The machines were operated with three different static rotor imbalances (U0, U1, U2) to test the imbalance influence on the fluting effect due to discharge and rotor-to-ground bearing currents. The damaging effect of inverter-induced bearing currents is influenced by the parameters “rotor speed”, “bearing temperature”, “bearing grease” and “grounding conditions” of the inverter-motor-system. The impact of a static rotor imbalance on the damaging process caused by the parasitic bearing currents is so far unknown. Therefore it shall be clarified, if the combination of static rotor imbalance and bearing currents may damage the bearing raceway surfaces much faster than without imbalance. As a concluding result our test procedures showed no acceleration of bearing deterioration due to static rotor imbalances.