On-line Monitoring System And Its Application For Urban XLPE Cable Insulation Status

With the vigorous development of the city and the continuous improvement of the requirements for urban beautification,cables have gradually replaced the overhead lines and become an important part of the power system.Therefore,online monitoring of cables and timely detection of cable faults are very important for ensuring the safe operation of the power grid.The meaning.In view of the shortcomings such as the one-sidedness and locality of the current online monitoring of cable insulation,and considering the influence of multiple factors,this paper proposes a method for evaluating the insulation state of urban cable based on fuzzy theory,and develops an online monitoring system for the insulation status of urban cable.First of all,this paper analyzed the reasons and the basic characteristics of partial discharge,based on the cause of cable insulation fault problems of urban power grid.According to the actual structure data cable,the equivalent simulation model of the parts of cable was build for the simulation analysis of the electric field distribution characteristics of cable under different fault conditions distortion including air gap,water gap,steel nail knocked.According to the cable insulation fault mechanism this article selected the characteristics that monitoring system required including capacitor leakage current,frequency pulse current,ambient temperature and relative humidity,and analyzed the correlation of the selection of characteristic and cable insulation state in detail.Secondly,considering the influence of the cable insulation state characteristic,using fuzzy comprehensive evaluation method for a comprehensive evaluation of cable insulation status,a evaluation method of cable on-line monitoring on the theory of fuzzy was proposed,which used fuzzy analytic hierarchy process for rational distribution of weights of cable evaluation factors,solved the problem of each evaluation factor’s membership degree with membership function and fuzzy set and completed the assessment of cable insulation condition.Third,cable insulation online monitoring system was constructed on basis of the theory.Hardware module and software programming including capacitor leakage current,pulse current,environmental temperature and humidity data of online monitoring,remote communication and solar battery charging function was completed.Network real-time data transmission platform which achieved real-time continuous on-line monitoring for cable insulation status changes in three different levels of warning was set up.The last one,the cable insulation online monitoring warning system was applied.On-line monitoring device was installed in the ten points selected to carry out effective field experiment.According to real-time data of three cables,data analysis and fuzzy evaluation of cable insulation state was conducted.The feasibility of fuzzy comprehensive evaluation method was validated by the analysis of the theoretical algorithm results and the actual measurement result.To verify the effectiveness of cable insulation status and feasibility of fuzzy comprehensive evaluation method,the theoretical algorithm results and the actual measurement status were analyzed,the results show that one of the cables was marked yellow warning by evaluation results and point of failure could be found through troubleshooting.