Detection of Partially Fallen-Out Magnetic Slot Wedges in Inverter-Fed AC Machines at Lower Load Conditions

Electrical machines in the high-voltage class are usually designed with open stator slots. This wide open slots cause an increase of higher order harmonics, vibrations, noise, and temperature; thus, the machine efficiency is decreased. To counteract this disadvantage, magnetic slot wedges are applied. Due to the impact of high magnetic and mechanical forces, these wedges can fall out and may cause further serious damages. Up to now, reliable detection methods for single missing slot wedges are coupled with a disassembling of parts of the machine. In this paper, a method is investigated which provides the possibility of detection, based on the measurement of electrical terminal quantities only.