Dielectric Properties And Space Charge Characteristics Of Nonlinear Dielectrics

Because of its good processing characteristics and insulating properties ofpolymers,which have been promoted hugely in the fields of electrical andelectronic insulation.The nonlinear insulating dielectrics not only can reducespace charge generation,but also can improve the electric field distribution in theinsulation structure.So the research on its dielectric properties has certain boththeoretical and engineering significance.In this paper, the non-linear compositematerials have been prepared by adding silicon carbide (SiC) with differentparticle sizes to low density polyethylene (LDPE) matrix.The author testeddielectric properties and space charge characteristics of nonlinear compositematerials, and made preliminary studies of the results of the measurements.Considering the possible of the application of the nonlinear insulation andlinear insulation combined, multi-layered compound samples have been preparedby the nonlinear composite materials and the pure LDPE, and for the furtherexperimental study. First, the DC current-voltage characteristics of compoundsamples have been tested. Compound samples of two-layer structure have beentested with nonlinear insulating materials put in high-voltage side and put in themeasuring side. Experimental results show that the testing of the DC current-voltage characteristics of the compound samples is alike, which have beencombined with micron nonlinear materials put in the different electrodes. Andtesting the DC current-voltage characteristics of the compound samplescombined with nano nonlinear materials. In low electric field section, thenonlinear coefficient of nonlinear materials putting in the measuring side isbigger than in the high-voltage side. In high electric field section, the nonlinearcoefficient of nonlinear materials putting in the measuring side is less than in thehigh-voltage side. Measuring compound samples of three-layer structure, theauthor found that, in double logarithmic coordinates, the relationship between theconductivity and the strength of electric field of nano three-layer compound samples presented two turning points, and the relationship between theconductivity and the strength of electric field of micron three-layer compoundsamples presented a turning point. Results show that the degree depending on theelectric field of the conductivity of nano three-layer compound samples washigher than micron three-layer compound samples.In order to study the microscopic changes after the combination ofmultilayer structures, thermally stimulated current of the multilayer compoundsamples have been measured in different polarization electric fields. In differentheating rate conditions, experiments found that the TSC spectrum of thecompound samples was not complete under the heating rate of1℃/min, and theexpressions of the depolarization information have defects. Thermally stimulatedcurrent of the multilayer compound samples have been measured under theheating rate of0.5℃/min, and got a perfect TSC spectrum and could reflect fullydepolarization information. Reasons may be the influence of the interfacepolarization of compound structures. The increasing of internal traps depth andthe changing of activation energy resulting in that the discharge processes slowdown, so it would take a long time to complete the discharge process.Finally, the role of the nonlinear composite materials restraining spacecharge as a barrier layer, has been studied. In different electric fields, differentvoltage time, space charge distribution of the multilayer compound samples hasbeen measured. Recoverying data of space charge measurement, becausewaveforms of testing data of the multilayer compound samples are not consistentwith settings of recovery software. So, in this paper, injections of space charge ofcompound samples have been analyzed through the original voltage signalfigures. The experimental results show that micron nonlinear barriers have acertain inhibition effect to the space charge injection, but the restraining effect ofnano nonlinear barriers was not good.