Surface charge and flashover voltage of EVA/CB nanocomposite under mechanical stresses

Ethylene-vinyl acetate (EVA) composite is widely used in cable accessories to uniform electric field and prevent partial discharge. However, local electric field distortion will cause charges accumulation and flashover, which is susceptible to the tensile strain upon the materials. Carbon Black (CB) nanoparticles can be applied to adjust the electrical properties of polymer composite. The effects of the CB contents on the surface charge and flashover characteristics of EVA/CB nanocomposite under various tensile strains need further investigation. In this paper, samples were prepared by incorporating CB nanoparticles into EVA matrix with fraction of 0, 1, and 5 wt% respectively. Tensile strains of 5, 10 and 15 % were applied to provide three deformations, which were compared with the unstretched sample. The dependence of the relative permittivity, surface charge decay and flashover characteristics on the CB contents under various tensile strains were measured. The trap distribution and carrier mobility were calculated to analyze the tensile strain dependent surface flashover. Obtained results show that the surface flashover voltage decreases with the increasing tensile strains for all the samples. Moreover, the flashover voltage of the samples doping with 1 wt% CB nanoparticles is higher than the other samples. The combination effects of trap distribution and carrier mobility are responsible for the above results. The surface flashover is more prone to occurrence under higher tensile strain, which should draw enough concern for the security of power cable operation.