The Research Of Fractal Theory And Wavelet Transform In DC System Grounding Fault Detection Application

It is important for power system to operate safely that DC system grounding faultdetection in power plants and substations is timely and exactly. The detection methodof low frequency signal injection widely used is easily influenced by the groundingcapacitors and the loop net. To solve the problem, this paper presents a new detectionmethod based on low frequency injection with wavelet transform and Fractal theory.The main contents of the research include:1. Summarizing the effects of grounding capacitors and the loop net to DCsystem grounding fault detection, and analyzing harmonious currents produced by theripple voltage during the process of commute and signal distortion influenced by CTsaturation;2. On the basis of analyzing the characteristics of signal in loop net and learningthe Fractal Theory and Wavelet Transform, a noval way of calculating the FractalDimension is used in loop net branch grounding fault of DC system;3. During the process of simulation, the scarcity of the way in 2 occurs. So areformative method that combines Wavelet and Fractal is used to identify loop netbranch grounding fault;4. Designing a part of signal transacting that uses Morlet Wavelet to partition thedifferent frequency and makes use of Wavelet Transform coefficient to calculateanother important parameter---concavo-convex parameter;5. Designing an algorithm based on the software of FD and Matlab, and testingthe feasibility through a lot of simulations;6. Setting up the simulating DC power supply net, primarily implementing thesimulation of real data of locale.This subject is very meaningful to perfect the detection of DC system grounding fault andrealize the safety and reliability of DC system. In addition, it helps the research of wavelet theoryand fractal theory in detection of DC system grounding fault in the future.