Reaserch Of Line Protection For Direct-current Distribution Network

In recent years,the power loads are increasing rapidly with the development of social economy.The AC distribution network have faced many problems,such as a lack of supply capacity,low power quality,limited delivery space and the access of distribute generator.To solve these problems,the concept of low voltage DC power distribution network is put forward and gradually accepted by the people.But it is becomes a new problem that the existing protection method of DC transmission line cannot be used in DC distribution network directly.And this problem will influence the development of DC distribution system.Therefore,it's has the very important theory significance and engineering application value to analysis the line faults in DC distribution network and research on the line protection.This paper researches on the characteristics of various faults which occur in multistage DC feeder with single supply firstly.Analysis the change of feeder current with the equivalent circuits of DC system.Take advantage of the currents and their changes rates which flowing throw the pole and neutral lines after faults to form the action judgments and ensure the selectivity of the feeder protection.Then,this paper summarizes the differences between single supply DC system and multiple supply DC system.The line protection method for multiple power supply DC distribution network are researched by analyzing the equivalent circuits of the faulty part when the converters are under different control method.The proposed method can cooperates with the current limiting measures of converters.The fault currents and their change rates are still as the action judgment of the DC circuit breakers.Finally,the simulation models of DC distribution system and its protection have been built in Simulink,which can be ran in the real-time simulation platform RT-LAB.The protection algorithm have been tested under various fault situations,the results show the protection algorithm can cuts off the faulty part of the DC network correctly.These studies will provide theoretical support and application reference to the development of DC line protection and DC distribution network.