Research On Protection Technology Of Cable Lines In DC Distribution Network

Compared with the AC distribution network,the DC power distribution technology based on the voltage source converter has significant advantages in terms of power quality,power supply capacity,and control flexibility.When the DC distribution network line has a pole-to-ground fault,the current is weak,and there is no reliable protection scheme and setting method.The pole-to-pole fault current rises extremely fast,and the protection fastness and selectivity are very high.Therefore,the relay protection technology of the DC distribution network line is one of the major problems that need to be solved urgently.This paper analyzes the fault characteristics of pole-to-fault and pole-to-pole fault of DC distribution network cable line,and studies the fault protection principle and setting method.The equivalent calculation method of the core line parameters of DC cable is studied,and the error of the simplified model of the line is analyzed.Firstly,the typical structure of the cable and the grounding method of the casing are summarized.The equivalent calculation method of the cable core parameters is studied.On this basis,the differences of equivalent circuit models in different methods are studied.The error of the model is compared and analyzed.The applicability of different line models in fault analysis and computational simulation of DC distribution lines is summarized.The pole-to-ground fault characteristics and protection schemes of DC distribution network cable lines are studied.Firstly,the grounding method of DC distribution system is introduced.Then,the charge and discharge current characteristics of the distribution capacitance of the cable line after the pole-to-ground fault of the DC distribution network are analyzed.The charge transfer of the line capacitance after the fault occurs is studied.Based on the difference,a pole-to-ground fault protection method based on line capacitance transfer charge is proposed.The characteristics and protection schemes of pole-to-pole faults in DC distribution network cable lines are studied.The fault transient electrical characteristics of the line are analyzed theoretically.The differential current characteristics of the internal fault and the external fault are studied.Based on this,the principle of the poleto-pole fault protection based on the system transfer charge is proposed,and the protection setting value is proposed.Aiming at the problem of data non-synchronization in the protection method,a differential current energy correction method based on sliding data window is proposed.In this paper,the pole-to-ground fault characteristics and the pole-to-pole fault characteristics of the cable line are analyzed.The protection principle and scheme based on the transfer charge amount are proposed.The setting method is simple and clear,and it has high practical value for the DC distribution network cable line.