Damper Winding Fault Detection in Synchronous Machines

Sammanfattning: This thesis aims to identify methods for detection of damper winding faults in synchronous machines (SMs) powered by variable frequency drives (VFDs). The problem of failing damper windings has received attention after reports of serious damage which have been discovered during maintenance checks. Since SMs often are used for critical applications, failures can be devastating if they cause total breakdowns. Also, VFDs are believed to cause additional stress in the damper windings of SMs and since the utilisation of VFDs is increasing, the problem is expected to become more common in the future. Currently, there is no method for detection of failures during normal operation of SMs, thus research in the area is required. Simulations based on the finite element method as well as laboratory experiments have been performed in order to examine the impact of VFDs and to find a way of detecting damper winding failures. The results confirm that utilization of VFDs produce higher currents in the damper winding compared to direct-online operation. The results also show that in case of a damper bar failure, the current distribution among the damper winding segments is affected. However, monitoring of all damper winding segments is unrealistic due to the number of sensors required. Another approach, which has been investigated, involves monitoring of the current through the pole interconnectors of one of the endrings. Potential fault indicators have been found by analysing the currents in the frequency domain. However, further studies are required in order to evaluate the method. Also the temperature of the damper winding was investigated as an indicator.