Studies Of DC System Grounding Fault

It's important for safe operating of power system that grounding fault detection of DC system is timely and precise in power planes and substations. Grounding capacitors and loop connections in branches severely affect the validity of current detection methods. To solve these problems, this paper presents a new low frequency injection method using wavelet transform theory and fractal theory. The main contents of the research include1. Through building the DC power system model, to analyze the traits of branch currents, and main problems in grounding fault detection.2. Analyzing and integrating current detecting methods, to focus on analyzing traits of these algorithms and their realizations, and to give an improved method.3. According to the characteristic of non-loop branches, presenting a new detecting method using wavelet transform theory. First, a preprocessing for current signals based on biorthogonal wavelet transform; then, to get low frequency components in current signals and voltage ones using complex wavelet transform; at last, to calculate the multitudes and phases of theirs, as well as the grounding resistance of the branch, according to proportional coefficient and linear phase.4. According to the characteristic of loop branches, presenting a method of wavelet fractal technology. First, to implement the frequency band division for current signal using multi-resolution analysis; then judging the insulation condition of the branch, referring to change trends of fractal dimensions.5. Presenting a complete grounding fault detection procedure and related hardware circuits in detection devise.6. Testing above detection methods using the signals from the DC system model convincing its precision and validity.The objective of this research is to perfect the grounding fault detection method and, to improve the security and reliability in DC system. Through analyzing current detection methods, the paper focuses on choice and realization of algorithms, which is meaningful for optimizing detection methods and developing detection devise.