Influence of Motor Operating Parameters on Discharge Bearing Current Activity

While the cause-and-effect chains of inverter-induced bearing currents have been well understood today, not much is known about the damage mechanism inside the bearings. Research has suggested that the bearing degradation is approximately proportional to the frequency of occurrence of the bearing currents. For bearing currents that occur statistically distributed-such as discharge bearing currents-this parameter has not been thoroughly researched yet. In this paper, we present an analysis of the influence of different motor operating parameters on the frequency of occurrence (“discharge activity”) of discharge bearing currents, using a non-intrusive detection method. When analyzed individually, the motor speed, motor shaft temperature, inverter switching frequency, and inverter dc-link voltage influence the discharge activity. However, the overall running time of the motor, the state-steady-state versus instantaneous-and the “operating history” on the time-scale of several days have the strongest effect on the frequency of the discharge bearing current occurrence.