Thyristor Rectifier-Embedded Identification of Field Winding, Damper Bar, and Eccentricity Faults in Wound Field Synchronous Machines

Detection of defects in the rotor of wound field synchronous machines (WFSM) is crucial as they can escalate into failures that can cause forced outage of the machine. The test methods commercially available for detecting field winding turn faults, broken damper bars, and eccentricity require machine disassembly and/or physical access to the machine, which lead to high maintenance costs. On-line monitoring options require installation of sensors on the stator bore or on the machine frame and are not sensitive to all rotor faults. In this paper, a new test concept for automated detection of WFSM rotor faults is proposed. The thyristor rectifier of the static field excitation system is used as the test equipment for injecting test signals into the rotor winding whenever the WFSM is stopped. It is shown that the $6^{\text {th }}$ harmonic rotor impedance measured at varying core saturation levels can provide reliable detection and classification of shorted field winding turns, broken damper bars, and eccentricity. An experimental study on 20, 30, and 100 kVA WFSMs under the $\mathbf{3}$ fault conditions is given for validation of the proposed test method.