Electromagnetic Analysis of Stator Ground Faults in Synchronous Generators

Abstract

There are many stator ground faults protection schemes available in the industry. These schemes relatively perform well in detecting the faults in the stator winding. The protection of the neutral point vicinity is the challenge because of the low voltage induced in that area. The 100% stator protection concept has been around for a long time. However, these schemes sometimes have limitations. The fact that stator ground fault detection in generators depends on many factors like the generator design, the generator loading, and the equivalent capacitance of the generator’s windings and the apparatus connected to it, occasionally caused these schemes to fail to detect the winding faults near the neutral or to miss-operate during normal system disturbance. In this dissertation, an electromagnetic analysis of the synchronous generators stator winding ground faults is presented. A mathematical model for the synchronous generator under stator winding fault is being derived. In addition, a study is conducted using 2D FEA simulation and verified using experimental testing on the third harmonic ratio under-voltage protection scheme. Another study focuses on finding a unique signature for the stator ground fault using wavelet transform. This analysis is an attempt to understand this phenomenon from the machine design point of view by looking at the generator terminal and neutral voltages. The analysis presented in this dissertation shows that the protection schemes perform positively in detecting stator ground fault. However, it does not show reliable performance under system disturbances. On the other hand, the wavelet method shows better performance and it reflects robustness against these disturbances.