Electrical Testing for Detection and Classification of Open Damper Bar and Shorted Field Winding Failures in Wound Field Synchronous Motors

Broken damper bars and shorted field winding turns degrade the starting and running performance of industrial wound field synchronous motors (WFSMs), and can lead to a forced outage of the motor and driven process. Testing of WFSM rotor windings mainly relies on off-line tests, which cannot be performed frequently and are known to lack reliability. Shorted turns in the field winding can be detected on-line from the airgap flux measurement, but require a sensor to be installed on the stator bore. In this paper, new test methods for detecting and classifying damper and field winding faults based on electrical signals are proposed. The proposed methods can provide remote testing at motor standstill and during the motor starting transient without disassembling the motor. Test results on a 30 kW, salient pole WFSM show that both test methods can provide reliable detection and classification of damper and field winding faults.