Research On PE-based Nonlinear Material And The Effect On The Electric Field Distribution Of High-voltage Cable

Cross-linked polyethylene(XLPE)insulating material has been widely used in the manufacture of high-voltage power cables of 220kV and below,and has been applied in the 500kV EHV Transmission Line.However,due to the low molecular weight byproducts produced in cross-linking reaction process of polyethylene and the cable insulation defects caused by many other factors in the process of cable manufacture,installation and operation,electric tree can easily be initiated in the high-voltage cable insulation during operation,and affects the working life of the cable.The application of nonlinear insulating materials,which can homogenize electric field distribution,to the manufacture of new structure high-voltage cables is likely to inhibit initiation and growth of electrical tree,and expected to bring good economic and social benefits.In this thesis,the PE-based and XLPE-based nonlinear insulating materials are prepared,the rheological and mechanical properties are tested,the laws how various factors affect the conductance characteristics and AC breakdown strength are researched,and the effect that the nonlinear shielding layer added in samples acts on the growth of electrical tree is compared and analyzed by experiment.Meanwhile,the electric field distribution around the point of electrical tree,which exists in samples and cables,is simulated and computed by COMSOL Multiphsics software,so does the electric field distribution around defects,which exists in the cable of traditional structure and new structure with nonlinear shielding layer.The results are shown as follows:when the SiC content reaches a certain value,increasing SiC dosage or adding CB can improve the nonlinear characteristic of conductance of the composites,and the preparation process of the composites,cross-linking and temperature also affect the conductance characteristics.The prepared composites have a better nonlinear characteristic of conductance,and the AC breakdown strength tested by adopting electrodes of different shapes has little difference.Adding a nonlinear shielding layer in the electrical tree initiation sample can greatly extend its pressure time and reduce the electric field distortion around the end portion of electrical tree.The nonlinear shielding layer added in the cable of new structure can significantly ameliorate the electric field distribution around defects,the metal burr tip of the wire core,the bulge in the surface of the semi-conductive shielding layer and the micropore in the surface of insulating layer,and effectively inhibit the initiation and growth of electrical tree.