Detection of Turn-to-Turn Faults in the Stator and Rotor of Synchronous Machines During Startup

An invasive diagnostic technique is proposed in this article for the detection and discrimination of turn-to-turn faults in the stator and rotor windings of synchronous machines during the startup period. For this purpose, search coils are installed in the machine to sense the rotational magnetic field along the air-gap circumference, while the difference in the related induced voltages (differential voltages) reveals its distortion, using it as a criterion for the detection of the faulty condition. Nevertheless, the rotor speed is a time-variant parameter, which changes from zero at the starting instant up to its rated value at a synchronous speed. Consequently, during the generator startup, the frequency of the induced voltages in the search coils needs to be updated continuously for obtaining reliable values for the differential voltages. A simple method is presented to achieve this goal by detecting the sequential zero crossing of the voltage waveforms. The proposed method is verified through simulation and experimental results. They show that the proposed diagnostic technique is capable of detecting and discriminating stator and rotor turn-to-turn faults during the machine startup period, both in generating and motoring conditions, with suitable accuracy and security. In addition, the region of stator turn-to-turn faults can be easily identified.