Breakdown And Electrical Tree Characteristics Experiment And Simulation Of Polyethylene Insulation Composites

With the wide application of polyethylene cables in power systems,it is preventing the breakdown of cables that plays an more and more important role in the stability of power transmission.However,electrical tree is a common phenomenon in electrical aging before the breakdown of insulation.Therefore,it is practical and important to study the breakdown of insulation materials and the electrical tree.In this paper,combining with the domestic and abroad researches,our research tested and simulated the breakdown and electrical characteristics of polythene-based insulating composites.In this research,polyethylene was used as the matrix,blending with linear low-density polyethylene,high-density polyethylene and polypropylene respectively to measure the breakdown field strength of the insulating composites.The Weibull distribution,which was used to fit and analyze the field strength data,was applied for finding the best component of the breakdown field strength.In this thesis,two different voltage boosting methods were utilized in the electrical tree samples.Observing the sample starting voltage,the shape of electrical tree and the growth rate of it under different voltages,we analyzed and explained the reasons for the formation and the changes in the growth of different types of electrical trees.The application of FDTG model calculated the local field strength at the front end of the tree with different pin spacings.The usage of MATLAB software simulated the WZ model of the growth of electrical tree and calculated the fractal dimension of the tree.The effects of changes in the growth coefficient,threshold voltage and electric field parameters in the tree of the model on the shape and fractal dimension of the tree were discussed.And with the appropriate parameters,the WZ model would be better to simulate the actual shape of the electrical tree.This thesis utilized the Pearson and Spearman correlation analysis methods to calculate the correlation between the breakdown field strength and the starting voltage of the insulating composites and the correlation between the fractal dimension of the electrical tree and the parameters of the WZ model.Finally,according to the the evaluation criteria of the correlation,we drawn the conclusion.