Probability model for discharge activities in bearings of converter-fed electric motors

Voltage source inverters in electrical drive systems are the main sources of possible mechanical degeneration inside the anti-friction bearings of downstream drive train components. In order to find the right countermeasures to avoid these parasitic effects, knowledge of the switching conditions of the converter and the subsequent effects are an important issue. This paper focuses on the converter´s inherent common-mode voltage and its impact on the mechanical drive train elements. Using an electrical bearing model, a method will be presented and discussed to approximate the probability for discharges in the bearings of converter-fed electric motors.