Research On Joint Monitoring Method For Cable Aging Based On Power Line Communication

Power cables,as the main carrier of energy transmission in distribution networks,are crucial for their safe and reliable operation.Due to the closed and compact structure of cables,online monitoring of their insulation status is a major challenge.This paper proposes a joint monitoring method of cable aging based on Power-line communication technology,aiming at the problem that the cables put into operation in the early stage are close to their life limit.The channel frequency response that can be extracted by Power-line communication equipment in the distribution network is selected as the characteristic parameter representing the cable insulation state,so as to realize online monitoring of cable insulation aging,The effectiveness and practical feasibility of the proposed method were verified through experiments and simulations under complex topology structures.The main research work of the paper includes:(1)Establish thermal aging and water tree aging models for cables.Due to both thermal aging and water tree aging accompanied by changes in the dielectric properties of insulation materials,considering the physical and frequency domain dielectric properties of cable insulation aging,and considering the different characteristics of high-frequency signal propagation and electrical signals in the cable,a distributed parameter model of the cable was established based on transmission line theory to study the impact of insulation aging on its distributed parameters.The results indicate that within the frequency range of 1-100MHz,the more severe the aging of the cable,the larger its propagation constant,and the smaller its characteristic impedance.(2)Using bottom-up modeling methods and reverse iteration ideas,establish a power line channel model to study the impact of topology and load variability on channel transmission characteristics in distribution networks.Combine the obtained cable aging model with the channel model to study the impact of different aging degrees and local aging lengths on channel frequency response in the transmission line.The results show that the more serious the cable aging is,the greater the selective attenuation of channel frequency response is.For the local aging that is difficult to detect,the Power-line communication method is still applicable.(3)Build random forest classification algorithm and random forest regression prediction algorithm,and adjust parameters according to the principle of the algorithm and the actual situation of this study.According to the characteristics that different aging types have different processing methods,the constructed random forest classification algorithm is used to identify the aging types of cables.In order to quantitatively describe the insulation state of cables,random forest regression prediction algorithm is used to predict the aging degree of cables.The practical feasibility of the proposed method in identifying aging types was verified by building an experimental platform.(4)The power line channel model under the Complex network topology structure is established to classify and predict the aging degree of cable insulation under fixed load and random load respectively.The simulation results show that the identification and prediction accuracy of the proposed method under fixed load conditions is higher than that under random load conditions,but the error generated under random load conditions is still within the allowable range,verifying the effectiveness of the proposed joint monitoring method for cable aging.The application of the method proposed in this article can not only identify the type of aging when the insulation of cables undergoes aging,but also quantitatively predict the degree of aging.Therefore,when the insulation of cables is severely aging,maintenance or replacement can be carried out to reduce the occurrence of insulation faults and improve the operational reliability of the distribution network.