Research On Stator Winding Internal Faults Of Synchronous Generator

Though the wind induction generation, the solar generation and the fuel cell have been propelled as hot research by the energy crisis problem, more than ninety percent of the whole world electrical power is generated by the synchronous machines yet. With the increase of power demand, the synchronous generator rating grows larger and larger. Down time on these large generators can be very costly and hence the protection of the generator becomes more strictly. The stator winding internal fault is a destructive fault in the synchronous generator, a great effort on its principle analysis and protection research is very necessary. It will not only be significant for the internal fault protection of the traditional DC-excitation synchronous generator, but also has good reference value for that of the special generator used for air and marine. Four objectives have been studied in this dissertation as follow.A coupled field-circuit mathematical model based on the multi-loop is created to analyze the internal faults in generator in this paper. The model can simulate short-circuit fault, open-circuit fault and eccentricity fault, and so on. The applicability of this model has been verified by the dynamic simulative experiment. Furthermore, the time-frequency steady or transient behaviors of synchronous generator's stator inter-turn fault at different generator running condition have been studied by FFT and Wavelet transform technique.And the air-gap magnetic field characteristic of the synchronous generator is analyzed with stator winding inter-turn short circuit fault, while considering the vibration eccentricity. Then the corresponding characteristics of electro-magnetic torque are obtained, especially the magnitudes and frequency variation of the instantaneous pulse torque. And the post-fault signatures of the terminal current, the excitation current and the stator terminal vibration have also been studied.For the current or voltage waveforms of synchronous generator are closely related to their operating conditions, the synchronous generator's steady and transient process with internal and external fault has been studied based on the fractal dimension with Rescaled Range (RS) analysis method. Through the fractal dimension analysis of the computer simulative data and the dynamic simulative experimental data, a lot of useful laws are obtained. Lastly, a new internal protection scheme using fractal dimension is proposed in this paper.Based on the extended park's vector approach (EPVA), a new method of reference frame conversion—the extendedαβ0 method is presented in this paper. Then the graphical representation and digital characteristic of the internal fault are obtained. Lastly, based on the DSP board and personal computer, this noninvasive approach is used to online detect and analyze the unsymmetric voltage and current caused by the stator winding inter-turn short circuit fault of the synchronous generator.