Prediction of motor bearing currents for converter operation

The mechanisms that lead to bearing currents have been known for several years. Empirical results have been collected for a few combinations comprising converter, motor and motor feeder cable. Although there are a series of remedial measures, the basic parameters which favor subsequent bearing damage, especially corrugation, have still not been adequately clarified. After a brief introduction into the theory of motor bearing currents, this document will present two models that allow these currents to be calculated in advance for any drive system. An algorithm is subsequently described which can be used to estimate the potential danger for an induction motor taking into account the temperature and the speed.