Research On Fault Location Method Of T-connected Line Based On Power Frequency Voltage Distributio

With the increase of power grid transmission capacity,the installation of high-voltage transmission line towers has becoming increasingly dense and different voltage levels of lines are interconnected.Moreover,the integration of new energy transmission and distributed power sources makes the lines more complex.The three-terminal transmission lines is simple and convenient,requiring only two ends of power supply and no need to build a new power supply at the third end.This saves a lot of transmission equipment and greatly saves economic investment costs.Therefore,the three-terminal transmission lines method is gradually being applied to transmission lines,especially in 110 k V voltage level transmission lines.Located in the southwest of Yunnan Province,a three-terminal transmission lines spans a complex geographical environment in mountainous areas.It is difficult to synchronize the voltage and current data of fault recording devices at different terminals,making it impossible to use synchronous data from multiple terminals for fault location.Therefor,the fault points are extremely difficult to troubleshoot.The three-terminal transmission lines is different from the two-terminal transmission lines,which has three branches are connected by tee-points,and the line impedance at the nodes is discontinuous.The voltage distribution along the transmission line can be change after the impedance discontinuity point,so it is not possible to directly calculate the electrical distribution behind the tee-point of the wire using the electrical variables at the terminal of the line.The traditional impedance method calculates the loop resistance based on the power frequency voltage and current after transient decay of the fault,which has low requirements for equipment.But that is susceptible to the influence of transition resistance and the accuracy and reliability of distance measurement are poor.Despite,the traveling wave method has high ranging accuracy and fast action speed,the refraction and reflection of voltage and current traveling waves at the tee-point which makes it difficult to identify the mixed fault traveling wave heads,resulting in significant ranging errors,and asynchronous issues need to be considered for double end traveling wave ranging.Therefore,this paper proposes a method for asynchronous fault location of threeterminal transmission lines based on power frequency voltage distribution.Due to the problem of low sampling rate in fault recording devices,so using the power frequency for fault location.By establishing a parallel uniform transmission line based on a distributed parameter model,the measurement error is reduced by calculating the voltage distribution along the power frequency modulus.Secondly,the inherent boundary of the three terminal line is used to calculate the voltage at the tee-point,and the fault section discriminant is constructed to identify the fault branch,so as to improve the accuracy of distance measurement.Generally,fault current remains stable after transient attenuation,so asynchronous fault free terminal voltage and current can be synchronized through their angle difference,thus achieving fault location of multi-terminal asynchronous data on threeterminal transmission lines.In order to fully utilize the fault characteristics in voltage and current,the parameters of different circuit modulus of the line are analyzed and calculated,and the fault location results for ground faults and multiphase faults are optimized through independent air modulus and ground modulus.In addition,a PSCAD/EMTDC electromagnetic transient simulation model for three-terminal transmission lines is established,and the robustness of the proposed fault location scheme is fully verified through simulation.