Stator Inter-turn Fault Detection of Synchronous Machines Using Field Current Signature Analysis

Our recent observations suggested that harmonics in the field current are very promising to detect stator inter-turn faults in synchronous machines. So far, an increase in some of the even harmonics in the field current has been reported to detect such faults. However no explanation has been provided for the cause of these harmonics. Moreover, the even harmonics can significantly increase with supply unbalance as well as time harmonics, which can lead to a serious confusion. Hence, in this study, an in-depth investigation was conducted to determine the origin of various harmonic components in the field current and their feasibility to detect stator faults. It was found that, owing to structural asymmetries of the field winding, some of these components clearly increased with stator inter-turn fault. The findings are helpful to detect faults involving few turns without ambiguity, in spite of with supply unbalance and time harmonics. Both simulation and experimental results are presented in this paper. The diagnosis results have also been verified using a rotor-mounted search-coil, which can also be used to detect even a one-turn stator fault very effectively