| The distribution network is an important infrastructure for national economic and social development.And it is responsible for the healthy development of the economy and the continuous improvement of living standards.The fast and accurate location of the fault for distribution network is one of the key technologies to ensure the safe and reliable operation of the power grid and reduce the time of power cut.However,the distribution network is at low voltage levels,where the small current grounding method is widely used.The characteristics of faults are weak especially single-phase ground faults,which makes it difficult to locate the fault.In addition,the interference of factors such as operating environment and noise has further enhanced the difficulty for fault location in distribution network.Therefore,the study of fault location technology that can be used in actual distribution network has important theoretical value and practical significance based on the actual operating conditions.The main contents of this paper are as follows:(1)The key technologies for distribution network fault location are discussed.A distributed multi-point fault location technology based on the theory of double-terminal ranging is proposed.Firstly,the feasibility of collecting fault voltage wave at the secondary side of distribution transformer is studied.Secondly,the influence of the A/D conversion and noise on the location accuracy are analized.The method for obtaining the simulation data of the fault location device is provided.Then,the characteristics of the line mode and zero mode component for the fault wave are shown.The Karenbauer transform is used to obtain the line mode component,which contributes to complete the fault location.Finally,considering the electrical structure of the railway 35 k V distribution network,a technology of distributed multi-point fault location based on the theory of double-end ranging is proposed.According to the design parameters,the PSCAD/EMTDC simulation model of the distribution network is built.The characteristics of single-phase grounding through transition resistance fault,two-phase shortcircuit grounding through transition resistance fault,and three-phase short-circuit fault are analyzed.(2)The technology that can determine the arrival time of fault wave head is proposed based on the improved gradient-wavelet transform.The influence of the A/D conversion,and environment and measurement noise are able to be decreased.First,based on the transient characteristics of the fault wave,the original gradient method is improved.The improved gradient method can effectively enhance the singular characteristics of the fault wave and filter out part of the high-frequency noise.Secondly,the localized time-frequency characteristics of the filtered fault wave is obtained by wavelet transform.Then,according to the established PSCAD/EMTDC simulation model of the distribution network and the proposed simulation data calculation method of the fault location device,the simulation data for location device in the case of single-phase grounding through transition resistance fault,two-phase short-circuit grounding through transition resistance fault,and three-phase short-circuit fault is obtained.Finally,the distributed multi-point positioning method is used to calculate the fault position.It is demonstrated that the method proposed in this paper has high location accuracy combineing with comparison examples.(3)The influence of strong noise interference on the fault location technology of the distribution network is considered.The method to determine the arrival time of the fault wave head based on wavelet filter-S transform and complete fault location is proposed.The noise resistance and location accuracy of the method could be further enhanced.First of all,the trends of wavelet coefficients for the fault traveling wave,the environment and the measurement noise are different with the decomposition scale.At the same time,the computing capacity of the fault location device should be considered.The wavelet modulus maximum filter is combined with the threshold filter to achieve better filter effect.Secondly,The S transform is used to obtain richer time-frequency characteristic information than the wavelet transforms.At the same time,the influence of environment and measurement noise on the fault wave modulus is reduced.The initial wave head of the fault wave can be accurately identified.Then,based on the established 35 k V distribution network simulation model,the simulation data of the location device under different fault situations are obtained.Finally,the effectiveness of the technology proposed in this paper is demonstrated by analyzing the results,which are provided through using the single S-transform method and the wavelet filter-HHT method to determine the arrival time.(4)In order to restore the actual fault scenario and verify the location accuracy of the proposed fault location technology,Real Time Digital Simulator(RTDS)and fault location device are used for real-time simulation.The effectiveness of the proposed technology is demonstrated.First,the actual fault situations are restored by RTDS.The fault wave characteristics of the distribution line is simulated when multiple types of faults occur under different neutral grounding methods.Secondly,the obtained fault wave signal is connected to the fault location device through D/A conversion and power amplification equipment.Finally,the location accuracy of the proposed fault location technology based on wavelet filter-S transform under different fault situations is analyzed.The test results show that the location accuracy of the proposed technology under the simulated fault situations by RTDS can meet the requirement,which is provided by the electric power industry standard "DL/T 357-2019 Transmission Line Traveling Wave Fault Location Device Technical Conditions". |
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