Research On Adaptive Reclosure Strategy Of The Flexible DC Transmission System

DC power grid is an important direction of the development of modern power grid.In order to ensure the safe and reliable operation of the DC grid,the DC line fault and its impact is a hot issue of power system.The fault rate of DC overhead line is higher,and the transient fault is the common fault type.Therefore,for multi terminal DC system or DC power grid,the reclosing of fault line will greatly improve the reliability of DC system.However,the reclosing of the breaker must be selective,otherwise there will be another surge to the transmission system,when the breaker closed before the fault disappears,and it is bad to the electrical equipment operating conditions,so it is necessary to identify the type of the fault before the reclosing.In this paper,the fault identification method of HVDC system is studied,and the reclosing criterion is designed.This paper studies the special problem of electrostatic field in HVDC transmission system,the difference between of high voltage AC system and HVDC system in electric field is discussed,and the introduction of ion flow problems in DC transmission is been made.Interpret the production mechanism of the ion flow and establish the equivalent model of the ion flow from physical significance.Combined with the engineering examples,the equivalent model of transmission lines is analyzed,and studied the fault pole residual voltage characteristics with the impact of ion flow.Based on the voltage characteristics,fault property identification method is proposed for a true bipolar DC transmission line.In addition,this paper briefly discusses the categories of DC circuit breakers,compares the working performance of different types of circuit breakers,and introduces the working principle of mixed type DC circuit breakers.Based on the voltage characteristics of DC circuit breaker,analyzed the difference of the voltage and current in the condition of permanent fault and transient fault.At the same time,this paper discusses the method to judge the fault character of DC line by using redundant module to increase the side voltage of converter station.The research in this paper is helpful to improve the efficiency of power supply restoration after transient fault and ensure the reliability of HVDC transmission system.