Research Of Protection Technology For DC Distribution System

DC distribution system based on pulse width modulation has advantages of high power quality, large transmission capacity, high reliability, simple structure, economy and low energy consumption etc. It is suitable for multiple access of distributed generations, and it promotes the development of DC appliances and “DC eco-house”. Therefore, it will be the development direction in distribution areas. Relay protection technology, which is one of the key technologies for DC distribution system, still stays in its infancy and needs further study urgently. Therefore, the research of protection technology for DC distribution system has important theoretical and practical value.Firstly, this paper systematically introduces the research situation about the protection technology of DC distribution system at home and abroad, including the protection of DC distribution in subway and ships and that in power systems. The fault location and isolation of DC distribution system are mainly introduced. Moreover, the achievements of protection configuration of typical DC distribution system are also stated. The key issues of protection in DC distribution system at present are discussed and its future development direction is given.Then, the components of DC protection system are described which include DC measurement equipment, protective relay and DC protection equipment. The basic topologies of DC distribution system are presented, and a radial DC distribution system model is built, which lays technical foundation for the analysis of fault mechanism and verification of protection principle as below.Moreover, the fault characteristic mechanism of DC distribution system is analyzed. The key point is to research the four transient stages of the DC distribution system once DC fault occurs in the voltage source rectifier. Correctness of the fault characteristic mechanism is verified through the theoretical analysis and fault simulation.Finally, according to the research course, the research focuses on the three kinds of protection principles in DC distribution system, which contains Two-section Current Protection(TCP), Distance Protection based R-L model(DP-RL)and Longitudinal Differential Protection(LDP). And the feasibility of the protection principles and schemes is verified through the simulation examples. The results suggest that TCP is suitable for the last section of the distribution, DP-RL is suitable for the single line system and the downstream lines in DC distribution system with branch nodes, and LDP is suitable the upstream lines in DC distribution system with branch nodes.