Air Gap Flux-Based Detection and Classification of Damper Bar and Field Winding Faults in Salient Pole Synchronous Motors

Recent cases of broken damper bars and shorted field winding turns in synchronous motors (SMs) have shown that rotor faults can degrade motor performance and lead to a forced outage of the motor and driven process. However, detection of SM rotor faults has not received much attention since SMs are not as common as induction motors. Detection of SM rotor faults is difficult, as the damper bar is active only under the starting or load transients, and shorted field winding turns result only in a slight increase in rotating asymmetry. SM rotor fault testing in the field mainly relies on visual inspection or off-line tests, and new test methods that can provide reliable detection of the faults without motor disassembly is highly desirable. In this article, new test methods for not only detecting, but also classifying the two types of SM rotor faults under motor standstill and starting are proposed. A finite element and experimental study on 1.1 MW and 30 kW salient pole SMs are provided to verify the proposed methods. It is shown that damper and field winding faults can be detected and classified with high sensitivity and reliability compared to conventional tests.