Research On Defect Location Method Of The Cable Based On Improved Time Frequency Domain Reflection

Power cables are an important carrier of power transmission,and ensuring the safe operation of power cable is of great significance to maintain the stable operation of the power grid.It is of great engineering value to study a method in time,which can detect and accurately locate weak defects in the cables without damaging the cable insulation.Domestic and foreign scholars have proposed a time frequency domain reflection technology to locate the defects in the cables,which provides a new idea for locating weak defects in cables.However,the current time frequency domain reflectometry(TFDR)technology related research is still in the initial stage,and the existing defect location algorithms are still inadequate.Therefore,this paper will improve the original time frequency domain reflectometry technology,in order to achieve accurate location of defects in the cables.The main work is as follows :First,this paper introduces the original time frequency domain reflection technology,and focuses on the signal analysis effect of three common time frequency analysis methods of short-time Fourier transform(STFT),S-transform and Wigner Ville distribution(WVD)on TFDR.An improved S-transform method is proposed to analyze TFDR signal.This method can adaptively adjust the time-frequency resolution according to the characteristics of TFDR signal,and there is no cross-term interference.Therefore,the time frequency characteristics of TFDR signal can be well analyzed.Based on the improved S-transform,this paper proposes a cable defect location method with TFDR based on the improved S-transform.Compared with the traditional methods,the defect location curve of the proposed method will not appear distortion and false peak,and the defect location result is more accurate.Then,the local defect simulation model of the cable is established by using the transmission line theory.On this basis,a simulation study of cable defect location is carried out.And the location effect of the proposed method is analyzed,including different positions,lengths,degrees and types of defects in single defect cable model.At the same time,the location effect of the method proposed is analyzed on multiple defects of different types or different degrees in the same cable.And compared with the traditional pseudo Wigner Ville distribution method and the smooth pseudo Wigner Ville distribution method,the superiority and effectiveness of the method proposed in this paper are verified by simulation.Finally,in the laboratory,an experiment platform for testing the defect location of the cable is built by using coaxial cables and power cables,to study the effect of the method proposed in this paper on the location of defects in actual cables.Different degrees and types of defects are made on the coaxial cable,to study the location effect of the proposed method on different degrees and types of defects in actual cables.At the same time,the intermediate joint of the long power cable is regarded as a defect,so as to study the effect of the proposed method on the defect location in the actual power cable.The experimental results show that compared with the traditional pseudo Wigner Ville distribution method and smooth pseudo Wigner Ville distribution method,the proposed method can more accurately reflect the location of the real defects in the cable.This paper has 44 pictures,8 tables and 101 references.