Study On The Synthesis Protection System In Underground LV Distribution Networks

With the development of automatic technology- in underground, the more requirements are raised to improve the continuity, reliability and security of underground power supply system. It is hence very important in theory and practice to develop the synthesis protection system in underground LV distribution networks. The main object in this thesis is to solve the problems of applying the intelligent control technology to synthesis protective system in underground LV distribution networks. Combined with the research of protective technology and intelligent control technology in power system, the control techniques and protective methods in the synthesis protection system of underground distribution networks are proposed. It has been successful to apply the intelligent protective system in underground LV flameproof switchgears. By testing and running in underground, it has been shown that the protective methods in the system are right, valid and practicable. The main studying aspects are the followings:1. The characteristics of underground LV distribution networks and the actual significance to develop the project are analyzed, and the developing histories of the synthesis protection and intelligent control technology are reviewed, In addition, the disadvantages of traditional synthesis protective system are pointed out, and the new detecting methods and control strategies applied in the measurement and control system are put forward. The testing results show that the detecting methods are correct and the control strategies are practical.2. According to the actual situations in underground LV distribution networks, the characteristics of the electrical faults occured in the system are theoretically analyzed, and relevant protective principles and control strategies are proposed on the basis of national relative standards. Some difficult problems like selective earth leakage protection, phase sensitive protection anddynamic overload protection have been resolved, which makes a new progress in underground protective technology.3. A new type of intelligent synthesis protective system cortrolled by the microcomputer AT89C52 has been designed, which performs the functions of not only voltage protection, current protection, earth leakage protection, phase open protection and gas lock, but also liquid crystal display, RS-232 serial communication and 4-20 mA current signal output. The perfect protective functions, favorable man-machine interface and powerful communication function make the system reach more advanced level than others.4. The large-scale programmable logic device CPLD is applied to design logical circuit in the protective system, which can improve the reliability, security and flexibility of underground LV distribution networks.5. On the basis of analyzing the electrical characteristics of interference sources in underground, the corresponding hardware and software measures of anti-interference are taken to increase the reliability of the protective system.The new synthesis protective system has been tested in intelligent control laboratory. It has been shown that the protective system runs stably and operates reliably. In addition, the technical specifications have fully met the requirements proposed in overall scheme. It has been proved by the mention above that the designing methods and strategies are right and practical.