Research On Application Technology Of Non-linear Insulating Materials In High-voltage Cable

With the development of power grid construction in China, the quantity demanded of the high voltage cable has been increased, and the higher operation reliability requirements have been put forward. At present, 500kV high voltage, below high voltage and EHV cable are mainly using XLPE.The long-term operation and experiences of using show that the electrical tree aging is one of the main factors which cause the high voltage XLPE cable insulation deterioration until destruction. The root cause of the electrical tree was produced in the high voltage cables insulation, such as the impurity of insulation structure, microporous and semi-conductive shielding layer defects caused the electric centralized, the electronic was infuse by high voltage electrode, thick insulation brought that the materials are not reasonable state of aggregation and residual stress, and so on. The nonlinear insulating material was named"smart insulation material"which has unique conductance characteristics. Its conductivity increase with the electric intensity to raise and it has the ability that the electric field distribution homogenization itself. The nonlinear insulating material was used in high voltage cable which can help the electric tree's produce and development, enhance the cable insulation breakdown strength and thin cable insulating layer thickness.This article was prepared by blending low density polyethylene / inorganic filler (nano-silicon carbide, carbon nanotubes, carbon black) non-linear insulating materials, and low-density polyethylene and linear with the suppression of a three-layer composite insulation samples to test the dielectric properties of samples, the nonlinear barrier layer on the barrier effect of electrical trees. The results show that the increase of nano-SiC content can increase the conductivity of nonlinear material and nonlinear coefficient, adding non-linear multi-layer barrier layer can effectively improve the breakdown strength of composite materials, and different nonlinear barrier layer on the multilayer dielectric constant and loss have a great impact, nonlinear barrier layer inhibited the electrical trees.Two new structure high-voltage cables are designed in this thesis (adding non-linear barrier layers on both side of the insulation and adding a non-linear in the middle of the insulation), COMSOL Multiphysics is used in simulating and analyzing the electric-field distribution in the cable. Simulation results show that: nonlinear barrier layer added on both sides of simulation can effectively homogenize the electric-field distribution of surface defects of cable insulation, and inhibit the initiation of electrical tree on the insulation surface. Nonlinear barrier layer added in the middle of simulation can block the growth of electric tree that caused in the insulation, and effectively inhibit the development of electrical tree.