Study On Fault Location Of Underground Cables

In China, most of coal mines are gas mines. Because of the complicated conditions, working surroundings, the possibility of power cable faults, if not dealt with opportunely, could bring about blasting. Thus, it is crucial to monitor the cable faults effectively and alarm it fast. At present on-line fault location for power cable is not matured, and power cable systems in coal mines are in great need of on-line fault location technologies. Thus, it includes important theoretic meanings and engineering values to investigate power cable fault location in mine. The paper mainly contains as follows:Considering the practical conditions of power supply and protection system under mine such as transformers'neutral point are not directly grounded and fault information usually got from one-terminal, this paper, according to traveling wave theory, use simulation tool-Matlab to build a model of cable system and analyze the characteristics of traveling waves triggered by main fault types in coal mine. It concludes that it will trigger effective fault transient traveling wave in the system where neutral point are not directly grounded and fault resistance have obvious influence over traveling wave head.Aiming at false extreme value possibly caused by modulus maxima of wavelet transform when it is used in analyzing fault traveling wave, this paper proposes a curve matching method based on wavelet by combing wavelet theory into curve matching method. It shows that this method not only reserves the smooth and monotonicity of original curve but also utilizes wavelet transform's well de-noising, and can get the accurate time when traveling wave get the bus. This paper also does some examples to show that a curve matching method based on wavelet deal with false value better and have higher accuracy than modulus maxima of wavelet transform method.This paper proposes a method - one-terminal impedance-traveling wave assembled fault location based on distributed system, which aims at solving some special conditions of power cable fault location like tradition GPS two-terminal synchronous methods can't be used in mine and fault information only can be got asynchronously. According to the distributed characteristics of power cable system, it will monitor the cables by distributed system and when fault happens, it can firstly judge fault range with multi-level diagnosis, then detect the range of fault location. Fault is located by impedance-traveling wave assembled algorithm, which combines the reliability of impedance method with high accuracy of traveling method. It can decrease error and retain the accurate fault location through impedance-traveling wave assembled algorithm. And it proves the validity of this method through examples.