Surface Charge Transport Characteristics of ZnO/Silicone Rubber Composites Under Impulse Superimposed on DC Voltage

Composites with nonlinear conductivity have been applied to modify the direct current (dc) electrical field distribution and accelerate the space charge dissipation in polymeric insulation. This paper focuses on the effect of nonlinear conductivity on the charge transport under an impulse superimposed on a dc voltage. The surface charge accumulation and dissipation properties of the zinc oxide (ZnO)/silicone rubber (SiR) composites under an impulse superimposed on a dc voltage are investigated by a 2-D surface potential decay test. The results prove that the homopolar impulse superimposed on the dc voltage intensifies the surface charge accumulation, leading to an increase in both the surface charge and area. Under a heteropolar impulse superimposed on a dc voltage, neutralization occurs first, and then, the heterocharges accumulate on the surface. The vertical charge transport to the ground and the horizontal movement on the surface are the two factors concerning the surface charge dissipation. The larger surface charge caused by a higher impulse voltage leads to an increase in the nonlinear conductivity, which accelerates the dissipation of the surface charge, and this effect becomes more obvious in composites with higher ZnO content. However, there is a special case, in which the positive surface charge dissipates slower in 15-wt% ZnO/SiR composites than in the undoped sample. It is deduced that the positive charges are more difficult to transport in the ZnO/SiR composites than the negative charges due to the charge transport mechanism of the n-type ZnO semiconductors with a back-to-back Schottky barrier of the grain boundary.