Research On Cable Defect Location Method Based On Transmission Coefficient Spectrum

As an important energy source,electric is widely used in all walks.With the intelligentization and complication of power systems,the application of cables has become increasingly widespread.Cable failures will affect electrical equipment and even the entire power grid.Cable failures can affect electrical equipment and even the entire grid,and that often evolve from early defects.If these defects are ignored,various types of irreversible cable failures may occur,posing a serious threat to the safe operation of the power system and social safety.Therefore,it is necessary to detect and locate cable defects.Most of the existing cable health diagnosis methods detect and locate irreversible cable faults.However,such faults have adversely affected the operation of the power system.It is even more important that we have the cable information and take action before the failure occurs.Therefore,it is significance to detect and locate cable defects in advance and to grasp the accurate information of cable operation abnormalities as early as possible.In recent years,the frequency domain reflection analysis method has attracted attention,by injecting a frequency sweep signal into a cable,obtaining a cable input impedance spectrum,and then analyzing the cable running state.Under high frequency conditions,the cable input impedance spectrum can reflect the characteristics of the cable itself,and a series of algorithms can be used to obtain information such as the location of the defect and the severity of the cable defect.Since the frequency domain reflection analysis method started late,there are still many deficiencies.For example,the ability to detect defects depends on the frequency,the presence of "positioning dead zones" and misjudgment points in the positioning curve.This needs to be solved from the essential relationship between frequency domain reflection analysis and cable defects.In view of the current situation that the frequency domain reflection analysis method is still not perfect,the research contents of this paper are as follows:1.By analyzing the law of cable input impedance characteristics with frequency,the relationship between input impedance spectrum and transmission coefficient is clarified,and the mechanism of aging defects on distribution parameters and transmission coefficients is found.A transmission defect spectrum detection and positioning cable aging defect is proposed.The method deduces the relationship between the S-parameter and the cable transmission coefficient,and determines the transmission coefficient acquisition method based on the S-parameter.2.Firstly,based on the IDFT analysis method,the cable aging defect positioning is realized,and then the positioning curve under different bandwidths is analyzed by the kurtosis,and the upper limit frequency threshold of the test signal is proposed.Compared with the existing methods,it is verified that the positioning method proposed in this paper has higher precision and resolution within the threshold range.3.By studying the influence of the upper limit frequency of the sweep frequency signal on the test results of the transmission coefficient and the positioning result,it is found that increasing the upper limit frequency will make the defect representation more obvious,but at the same time,the introduction of error will not be conducive to the acquisition of defect information.And through comparison,the upper limit frequency threshold based on the transmission coefficient spectrum localization method under the existing test joint is preliminarily determined.4.Since the defect severity is positively proportional to the distortion amplitude in the positioning curve,a new positioning method based on the secondary transmission coefficient model is proposed to improve the positioning effect of weak defects in cables.First analysis of input impedance spectrum achieve cable aging positioning principle and defects of different impact on the distribution parameters,summed up the two distribution parameters,then according to the distribution parameters,deduces sensitive can reflect the physical defects of secondary transmission coefficient model,and puts forward a kind of based on S parameter measurement and construction method of secondary transmission coefficient of the model is verified by comparison can be more sensitive to reflect the physical defects,namely through the secondary transmission coefficient model can find physical defects,much earlier than the input impedance and can reduce test bandwidth,improve the application range of frequency domain reflection method.At the same time,the integral transformation algorithm was improved,and the physical defect of the cable was successfully located by using the secondary transmission coefficient model.5.The influence of input signal sweep points on the positioning results was explored,and a positive ratio was found between the resolution of the positioning map and sweep points.It was also analyzed and verified that the phenomenon was caused by the reduction of sweep points and the distortion of spectral lines,which resulted in the imperfection that could not be fully reflected in the transmission coefficient spectrum.This phenomenon is reflected in the localization map that the amplitude of the defect is proportional to the number of sweep frequency points,but the essence is that the defect detection ability of the transmission coefficient spectrum is proportional to the number of sweep frequency points.