Location Method Of Combined Single-end Fault For Transmission Line Of LCC-VSC Hybrid HVDC

Under the background of “ubiquitous power internet of things(UPIo T)”,high voltage direct current(HVDC)transmission plays an increasingly prominent role in the construction of national energy interconnection.As a new type topological structure of HVDC transmission system,(line commutated converter-voltage source converter,LCC-VSC)hybrid HVDC combines the technical and economic advantages of line commutated converter based HVDC(LCC-HVDC)and voltage source converter based HVDC(VSC-HVDC),and has good application prospects.Because of the long HVDC transmission line and the bad operation environment,it is difficult to patrol the line manually.Thus,accurate and reliable fault location is particularly critical to ensure the safe and stable operation of the power system.However,the fault characteristics of LCC-VSC hybrid HVDC transmission line are different from those of LCC-HVDC and VSC-HVDC transmission line due to different boundary elements at both ends.Therefore,it is necessary to study a new fault location principle for LCC-VSC hybrid HVDC transmission lines.In this paper,the catadioptric process and propagation characteristics of fault traveling waves for LCC-VSC hybrid HVDC transmission lines are analyzed in depth,and compared with those on transmission lines of LCC-HVDC and VSC-HVDC.It is concluded that it is impossible to distinguish the reflected wave of fault point from the reflected wave of bus terminal to realize single-ended traveling wave fault location by utilizing the polarity of wave head.According to the difference of frequency-varying characteristics of reflection angle between two ends of transmission line,the reasonable installation side of single-end fault location device in LCC-VSC hybrid HVDC transmission line is determined.A novel location principle of combined single-end fault is proposed.Firstly,the location method of natural frequency fault whose accuracy is slightly lower is utilized to roughly locate the fault point and obtain approximate arriving time of the first reflected wave from the fault point.Then,based on the symmetry between the arriving times of the first reflected wave head from the fault point and that from the opposite bus of line,the precise arrival times of these two reflected waves are found by matching in traveling wave propagation sequence diagram.Finally,the fault point is accurately located with the arriving times of the initial traveling wave,the first reflected wave from the fault point and that from the opposite bus of line.In order to detect the fault traveling wave head and extract the natural main frequency,this paper studies the traveling wave head detection algorithm based on ensemble empirical mode decomposition(EEMD)and the traveling wave natural dominant frequency extraction algorithm based on multiple signal classification(MUSIC).Both of them have better advantages in traveling wave signal processing.The simulation results of LCC-VSC hybrid HVDC transmission system based on PSCAD simulation software show that the combined single-terminal location principle proposed in this paper can accurately locate the fault point on the transmission lines of the LCC-VSC hybrid HVDC,and has higher engineering practical value.