Method Of DC System Grounding Fault Detection Based On Wavelet Transform

Generally speaking, it is important for safe operation of power system that DC system grounding fault in power plants and transformer substations is detected timely and exactly. The detection method of low frequency signal injection, which is widely used, is easily influenced by the capacitors between ground and each branch and by the ring net. To solve the problem, this paper presents a new detection method based on wavelet transform and low frequency injection. The detailed researches have been carried out and the main contents of the research include:1. Analyzing the main factors that influence the detection of DC system grounding fault,and the composition of branch current.2. Proposing a general scheme of DC system grounding fault detection on the base of wavelet transform theory in order to eliminate the influence of the capacitors between ground and each branch, and the ring net.3. Designing a novel algorithm based on the filtering preprocessing of B-spline wavelet according to the characteristic of branch current.4. Proposing a proportional divisor method and a fiducial signal method based onthe damped complex wavelet transform coefficients and proving them in theory. Putting forward a method of low-frequency current extraction on the base of damped complex wavelet. 5. Constructing an inverse complex wavelet transform algorithm for specific signal. Proposing the methods of low-frequency current extraction based on Morlet wavelet transform and wavelet packet transform respectively.6. Designing a Fourier-algorithm-based software to calculate the value of each branch's insulating resistance and validating the detection method through system simulation.7. Setting up the simulating DC power supply net, designing and implementing basically the signal acquisition and processing system based on the computer control technique.This subject matter is very meaningful to improve the detection of DC system grounding fault and to perfect the safety and reliability of DC system. In addition, it helps the research of use of wavelet theory in detection of DC system grounding fault in the future.