Research On Characteristics Of Electric-thermal Field And Fault Diagnosis Method Of Cable Terminal Under Internal Discharge

In recent years,with the rapid development of science and technology and rapid economic growth in our country,large-scale transformation and new construction of urban and rural power grids have been carried out.Power cables have occupied a dominant position in the power transmission and distribution of the power system.XLPE cables are widely used because of their good electrical properties and large current carrying capacity.According to the investigation and analysis of cable faults,the cable terminal has a complex structure and contains multiple layers of accessory materials.It is the weak link of the power cable.It is easy to produce insulation defects during production or installation and long-term operation,resulting in local field strength distortion,partial discharge and local abnormal temperature rise,and further cause cable failure,reduce the operating stability of the power cable.Therefore,the development of electrical-thermal field characteristics,partial discharge characteristics analysis and fault diagnosis methods of cable terminals has important engineering significance for the stable operation of the power system.Based on the background and current situation of the subject,this article has an in-depth understanding of the internal structure of the intact and faulty cable terminals,and detailed investigation and analysis of the weak points and causes of the cable terminal failures;for typical defects,the cable terminals are divided from the electric heating field characteristics and the local Three aspects of discharge characteristics and fault diagnosis methods of cable terminations have been studied in depth.First,based on the anatomical results of the cable terminal,establish a three-dimensional simulation model of the XLPE cable terminal with intact and typical defects;learn the theory of electric and thermal field coupling,verify the correctness of the simulation model based on the standard IEC60287 and infrared thermal imaging tests,and carry out the COMSOL finite element simulation software analysis of the characteristics of the electric heating field and the simulation results show that the field strength distortion and abnormal temperature rise at the defect are the main factors that cause the cable terminal fault;in addition,a diagnosis method of the fault degree is proposed based on the thermal field characteristics.Secondly,this paper built a partial discharge detection platform,produced XLPE cable termination samples with typical defects,and explored the partial discharge characteristics of XLPE cable terminations under typical defects.The research results showed that:different defect types under different discharge times,the similarity and difference of PSA and PRPD spectra can provide a good reference basis for texture feature extraction and fault diagnosis.In addition,the smallest difference between the positive and negative half-cycle skewness of the PRPD spectrum|ΔS_k|_min reflects that the defect type has good sensitivity.Finally,this article combines PRPD spectrogram and PSA spectrogram characteristics,establishes the PRPD-PSA library,designs a variety of feature extraction schemes,and realizes fault diagnosis through RBF neural network algorithm.The research results show that the fusion of GGCM-GMRF to extract the texture features of the PRPD spectrum and the PSA spectrum,and the recognition scheme based on the RBF neural network algorithm has the best effect.In addition,this paper screened and optimized the feature quantities used for identification and obtained a more effective identification method.