Experimental Investigation Of Space Charge Behavior In Non-linear/Linear Insulating Composite Structrue

The suppression technology of space charge is the key to make polymer dielectric can be successfully used in high voltage and ultra-high voltage DC power cables.Many scholars at home and abroad have been exploring the best way to suppress space charge in polymer insulation for many years.The nonlinear insulating dielectrics not only can reduce space charge generation,but also can improve the electric field distribution in the insulation structure.In this paper,a new space charge suppression technology has been explored.In the new space charge suppersion technology,a nonlinear dielectric layer between the semicon and the polymer main insulation is used as barrier layer to limit the space charge injection.The optimum of space charge suppression can be achieved by adjusting the type and the filling ratio of the filler.The non-linear composite materials have been prepared by adding nano Silicon carbide(SiC),nano Titanium dioxide(TiO2)and nano Barium titanate(BaTiO3)to low density polyethylene(LDPE)matrix.Multilayer compound samples were made from the nonlinear composite matierials and the pure LDPE.The author has tested the dielectric properties and the space charge characteristics of the multilayer compound samples,and has made a preliminary analysis of the results.Experimental results show that the conductivity characterisitic of composite materials modified with nano additive is non-linear and the variation of conductivity depends on the properties and the filling rato of the filler.It is found that there is a piecewise linear relationship between electric field and conductivity in the double logarithmic coordinates by V-A characteristic test of the multilayer compound samples,and the nonlinear coefficient increases gradually.The conductivity characteristics of the same compound multilayer sample are different under different voltage polarity.In the double-layered compound sample prepared by non-linear composite materials and the pure LDPE,the more the concentration of SiC is,the more different of V-A characteristics is.But the concentration of TiO2 and BaTiO3 have a little influence on the the polarity effect of V-A characteristics.The space charge tests show that the nonlinear insulating barrier can restrain the injections of space charge into polymer.This inhibition is related to properties,concentration and the applied voltage polarity.It can be inferred that the nonlinear barrier to restrain the space charge effect will be greatly improved by modifying and optimizing of the nonlinear barrier materials.