Research Of Fault Location Method Of AC Transmission Lines Sharing Tower With Dc Transmission Lines

Locating the fault quickly and accurately after the transmission line fault occurs not only can reduce the workload of line inception,but also repair the fault quickly,which can satisfy the demand for stability,efficiency and safety of operation of power grid.At the same time,along with the increasing shortage of corridor resources in our country,multi-circuit transmission lines with same tower are widely used.In recent years,technology of HVDC transmission has been widely applied,causing the situation that AC and DC transmission lines on the same tower appears which would be more common in the future.When ground faults occur in AC transmission lines with DC transmission lines on the same tower,complex fundamental frequency paths in the coupled DC lines will lead to the large difference of fault characteristics between AC/DC transmission lines on the same tower and tradition AC multi-circuit transmission lines,which will cause large error of fault location.However,at present,the research on fault location in AC/DC transmission lines on the same tower is still insufficient.Therefore,it is of great significance to study the fault location methods of AC transmission lines with DC transmission lines on same towers.The main content is summarized as following:Firstly,the electromagnetic transient simulation model of a AC/DC transmission system sharing same towers is built.The model includes AC transformer,DC converter and inverter station,AC double-circuit transmission lines,DC bipolar lines and AC/DC share tower transmission lines.Based on the simulation model,the grounding fault of AC line is simulated.The fundamental frequency current and voltage along fault AC line,non-fault AC line and DC bipolar line are observed.The power flow direction of fundamental frequency short-circuit power in AC and DC system when AC line grounding fault occurs is analyzed.It established a foundation of model for fault analysis and fault location.Secondly,in order to analyze the grounding fault characteristics of AC transmission lines sharing same towers with DC transmission lines,grounding fault simulation of AC transmission lines sharing same towers with DC transmission lines is carried out on the built simulation model.Analysis of characteristics of distribution of sequence voltage along AC transmission lines after grounding fault occurs.According to the difference of characteristics of distribution of sequence voltage,zero-sequence fundamental frequency is chosen to be used in fault location.Based on this,the zerosequence fundamental frequency mathematical model of AC and DC lines sharing same towers are constructed,and the relationship model between voltage and current along lines on AC/DC coupled section and non-coupled section are deduced.Then the influence of fault position and different operation modes of coupled DC transmission system on the distribution of zero-sequence voltage along AC transmission lines is analyzed.Finally,the AC/DC transmission lines sharing same towers are divided into three sections: double-circuit AC lines,bipolar DC lines and AC/DC lines on same towers.Based on deduced relationship model between AC zero-sequence voltage and current,DC fundamental frequency voltage and current along lines on each section.considering the influence of zero-sequence distributed capacitance,each section of lines are substituted by equivalent circuits of type in series,so that the zero-sequence component equation of fault location of AC transmission lines sharing towers with DC transmission lines is built.Then the zero-sequence compensation voltage along the AC transmission line is calculated by using the equation of fault location and the voltage,current information on each side of AC/DC transmission lines.According to the minimum difference of zero-sequence compensation voltage calculated on both sides,the fault location is determined.Thus a double-terminal fundamental frequency domain fault location method for AC transmission lines sharing same towers with DC transmission lines is proposed.At last,on the built electromagnetic transient simulation model,large numbers of fault simulation,including different operation modes of coupled DC system and different position of fault on AC lines,are carried out to verify the accuracy of the proposed method.