Small Current Grounding System Based On Wavelet Theory, Single-phase Ground Fault Study

Modern power system is a large and complicated power network integrated with power generation, power transformation, power transmission, power distribution and power application. Covering many different areas, it has a complex structure with lots of components inside. As power system plays a very important role in our national economy, it is necessary to make sure that the power system can run safely, reliably and economically. When electrical accidents really happen, varieties of high and new technologies are needed in order to eliminate or isolate the faults without any delay.Wavelet analysis is one of the major achievements of 20th century's mathematical research. It draws on the essence of modern analytics, such as functional analysis, numerical analysis, Fourier analysis, spline analysis, harmonic analysis and many other mathematic subdisciplines. Thus, wavelet analysis has a solid theoretic basis as well as a wide range of practical applications, of which power system is a promising one. And this dissertation mainly discusses the function of wavelet analysis in detecting and locating the single-phase-to-earth fault of low-current grounding power system. Low-current grounding power system, called neutral indirect grounded system as well, is a widely-used neutral grounded system in our medium and low voltage network. It can greatly reduce the current when earth fault occurs. However, the detection of fault current thus becomes more demanding. In such case, the fault can be detected promptly and accurately by applying the wavelet analysis because of its locality and singularity of signal process.First of all, it analyzes the network features and fault characteristics in low-current grounding power system;Then it goes into the details of the theory of wavelet analysis and its application in power system, and related system models are built and simulated by power system emulation in Simulink under the environment of MATLAB6. 5. Then, via wavelet analysis, the obtained data of voltage and current is under screen sizing and comparison, and Simulink simulation experiments of various grounding modes and faults are carried out. The focus of Chapter 6 is the programming of wavelet analysis software for power system;under the integrated exploiting environment of Delphi7.0 and combining the numerical calculating function of MATLAB6.5, object-oriented wavelet analysis software is programmed for the power system. Finally, at the end is the summary of this dissertation as well as the prospect for the future study.