Investigations on bearing currents in converter-fed electrical motors

As shown in [6], the issue of current flowing through a motor bearing is a system-related topic. Different aspects have to be taken into account to identify countermeasures to avoid or dampen the current flow. Up until now, it is not possible to define clear limits where the changes in the bearing raceways lead to the so called corrugation and with this to a possible bearing failure. This paper shows the latest results that were obtained with the investigation schematic presented in [6]. New results in the area of field experience with the so called “Bearing Current Sensor” (BCS) will be discussed. Additional results in the area of parameter tests, which take into account the dependency of temperature, speed, voltage as well as the type of lubricant grease, are shown.