Research On Fault Location Based On Wavelet Analysis For HVDC Transmission Lines

High voltage direct current transmission(HVDC)has played an increasingly important role in high-power and long-distance transmission,because of its simple structure and good performance.Compared with the traditional high voltage alternating current transmission(HVAC),HVDC has many advantages,such as good control performance,lower cost,no problem on power-angle stability and so on.Due to the long HVDC transmission line and the complex geographical environment in practical engineering,once the fault occurs in the transmission line,it is difficult to find the fault point.In order to reduce power loss and improve power security,it is urgent to develop reliable technology of fault location for HVDC transmission lines.Accurately identifying and detecting the line fault signals are key to realize the fault location for HVDC transmission lines.In this paper,the fault transient traveling wave signals,which are obtained by single pole and bipolar fault of transmission lines,are analyzed by using the signal processing method of wavelet analysis,and the distance between the fault point and measuring point is calculated by the fault location method of traveling wave.The main research work is as follows:Firstly,the simulation model of±500kV HVDC transmission system is built by the electromagnetic transient simulation software PSCAD/EMTDC,based on the self-contained CIGER HVDC Benchmark model of the software.The simulation results show that the normal operation and the ground fault of the transmission line can be simulated by the model.Secondly,the basic theory and fault location of traveling wave are introduced.The basic theory of traveling wave includes the generation of transient traveling wave,the transmission characteristic of transmission line traveling wave,and the reflection and refraction of traveling wave.In view of the coupling between the poles,it is proposed that the phase mode transformation can be used to decouple and obtain the line component for signal analysis.The traditional traveling wave methods include single-ended ranging method and double-end ranging method,and they are affected by recognition of initial traveling wave head and the value of traveling wave velocity.So the signal processing method of wavelet analysis is proposed to extract the traveling wave head,and fault location methods of traveling wave which are not affected by the wave velocity are used to eliminate the influence of wave velocity on the accuracy of ranging.Thirdly,the related theories of wavelet analysis are introduced,including continuous wavelet transform,discrete wavelet transform and binary wavelet transform,multiresolution analysis and porous algorithm and so on.The cubic B-spline dyadic wavelet and the feasibility of the modulus maxima theory of wavelet transform in traveling wave location are emphatically introduced.Finally,the signal processing method of wavelet analysis is proposed to analyze the bipolar fault signals.From the single-pole short-circuit ground fault,wavelet analysis is used to deal with the traveling wave head,and fault location methods of traveling wave are used to locate the transmission line fault.The results show that the double-end ranging method which is not affected by the wave velocity has the highest positioning accuracy.And then it is used in the study of bipolar fault combined with wavelet analysis.The results show that the wavelet analysis is feasible in the study of bipolar fault location.