Research On Single Terminal Fault Location And Protection For DC Distribution Lines

With the development of social economy,the rapid increase of regional power load,AC distribution system is facing with the pressure of limited transmission corridors,insufficient power supply capacity and reduction of power quality after distributed generation accessed.In recent years many scholars have begun to research on DC distribution system.As the key technology for DC distribution system,fault location and protection are related to the safe operation of the whole system.It is of great engineering significance to research on fault location and line protection technology of DC distribution line.In this paper,the radial DC distribution system is taken as the research object.Firstly,topological structure,control mode,steady state and fault transient operation of the system are analyzed.Secondly,the simplified line model of cable distributed capacitance is neglected in the existing research.The single terminal fault location equation considering cable distributed capacitance of DC distribution line is derived,which contains only two unknown parameters of fault distance and transition resistance.Then,based on parameter identification thought,the least square algorithm is used to solve the location equation,and the fault location is obtained.DC distribution system model is built on the power system real-time platform RT-LAB.The proposed fault location method is tested under different transition resistance and different fault location.The results show that the single terminal fault location method of the DC distribution line considering cable distributed capacitance is effective.On the other hand,DC distribution line protection is researched.Protection criterion is built by using difference fault transient current energy in different location,and db wavelet is used to form protection algorithm,then step action time limit is combined to form line protection scheme.Finally,for the single terminal DC distribution system,DC voltage,is ±750V,the effectiveness of protection scheme is verified under two typical fault condition of unipolar grounding fault and pole-to-pole fault.Based on power supply of two terminals DC distribution demonstration project in Shenzhen Baolong industrial district,the DC voltage of the project is ±10kV,protection method is tested once more.The results show that the transient current energy protection method is effective.