Research On Multi-point Hybrid Transmission Line Fault Traveling Wave Ranging Based On HHT

With the efficient and rapid development of China’s national economy,the requirements for distribution networks are becoming higher and higher,including more advanced technology applications,higher transmission efficiency and reliability,better adaptation to the development needs of urban aesthetics and better protection of the ecological environment.Overhead-cable hybrid transmission lines are one of the solutions to these requirements due to their high transmission efficiency,reliability,environmental friendliness and energy efficiency,low land use,high interference resistance and low maintenance costs.However,overhead-cable hybrid transmission lines have a large error in accurate fault ranging in the distribution network due to discontinuous wave impedance in the line,uneven line parameters and complex and variable fault transient traveling waves,so it is important to find the fault point quickly and accurately to restore power supply and reduce production losses.To address this problem,a multi-point hybrid transmission line fault ranging method based on Hilbert-Huang Transform(HHT)is proposed in this thesis,and the following aspects are investigated:Firstly,the domestic and international research on fault ranging methods for hybrid transmission lines is analysed and the use of the traveling wave method is proposed as the basis for the fault ranging method in this paper.The basic principles of six types of traveling wave method fault ranging are also analysed and compared,and the D-type double-ended ranging principle is finally selected as the basic principle of fault ranging in this paper.Then,by analysing the nature of fault traveling waves propagating on overhead-cable hybrid transmission lines,and based on the double-ended ranging principle,the multi-point ranging equation used in this thesis is proposed.Secondly,the HHT is proposed to decompose the fault transient signal after comparing the advantages and disadvantages of Fourier transform,wavelet method and HHT algorithms for the characteristics of the travelling wave signal.The Hilbert transform is then applied to the first component of the intrinsic mode function to obtain its Hilbert spectrum,and the time point corresponding to the abrupt change in the Hilbert spectrum is used to confirm the arrival of the wave at each wave collector.Finally,the HHT is used to extract the moment of arrival of the fault traveling wavehead at the measurement point,which is then substituted into the multi-point ranging equation to calculate the fault ranging results for overhead-cable hybrid transmission lines.The MATLAB/PSCAD simulation results show that the proposed method avoids the influence of the travelling wave speed on the ranging accuracy and is not affected by the line structure,and that it is more accurate than the traditional double-ended ranging method and wavelet method,and also meets the requirements of engineering practice for positioning.