Bearing Wear Condition Identification on Converter-fed Motors

This paper deals with the bearing wear and the early detection of possible damages in bearings of variable-speed, converter-fed electrical motors. A description covering the issue of bearing currents in converter-fed drives is presented. However, this work focuses on the practical experiences of bearing wear influence on electric motors performance. Explicit information concerning a bearing damage due to corrugation caused by electrical currents through the bearing can only be extracted by a combined analysis of the electrical and the mechanical behavior of the bearing. For this purpose systematic measurements have to be exploited, where both the electrical measurement of bearing currents and the mechanical measurement of the bearing vibration status have to be combined for determining the bearing condition state. A comparison between different vibration measurement methods provides a systematic approach enabling detection and classification of possible changes in bearings of the drive system i.e. motor and the attached load machine, in a very early state. Finally, a description of the possibilities to determine the electrical bearing load in a drive system and the correlation of its possible limit values to the mechanical bearing condition is highlighted.