316 / 2018-09-26 00:18:31

Conductivity and Surface Charge Properties of HTV SiR/SiC Composites under Impulse Superimposed on DC Voltage at Different Temperatures

HVDC cable accessory,silicone rubber,nonlinear conductivity,impulse superimposed DC voltage,charge carrier mobility

The nonlinear conductivity material has advantages in the modification of local field. Some inorganic fillers in polymer matrix provide a high conductivity at high field, which automatically accelerates the dissipation of the interface and space charge. The nonlinear conductivity composites can be applied to modify the local electric field distribution and accelerate the surface and space charge dissipation in HVDC cables. This paper focuses on the effect of the nonlinear conductivity on the charge transportation under impulse superimposed DC voltage. The surface-charge-accumulation property of silicone rubber (SiR)/SiC composites under impulse superimposed DC voltage is studied. The surface potential decay (SPD) is measured after the sample is stressed by the impulse superimposed DC voltage. The effect of the nonlinear conductivity on carrier mobility is analyzed. This research may provide some clues for analyzing the horizontal movement of the interface charge in the HVDC cable accessory insulations since the horizontal movement of the interface charge is hard to detect, especially when a failure point occurs on the interface. The threshold field decreases and the nonlinear coefficient increases at high SiC content. Referring to the percolation theory, the filler particles can form a conductive network when the filler volume fraction is large enough. High corona charging voltage provides more potential energy for the carriers to arrive at the surface of sample, which further accelerates the accumulation of surface charge during the charging process. The more surface charges accumulate on the surface, the higher electric field in the bulk of sample in the SPD process will be. The results prove that under DC voltage, the decay rate increases for the rise in the initial surface potential (ISP). Higher surface potential caused by higher impulse voltage leads to a larger nonlinear conductivity, which immediately dissipates the surface charge. The increase in DC voltage is proven to be more effective in accumulating surface charge than the impulse. The long time DC voltage can continuously drive the charges to move to the sample surface while the repetitive impulses cannot provide charges with enough energy without the impulse peak. The repulsion and the diffusion are two factors concerning the ISP. They become dominant in different cases. The repulsion effect depends on the number of the existing DC voltage charges. The diffusion effect comes into effect when the rise in repetitive impulses brings additional charges. The vertical movement to the ground and the horizontal movement of surface charges are two factors concerning the ISP and SPD, which are both affected by the nonlinear conductivity of SiR/SiC composites.