Mechanism of SiC Coating on Surface Charge Behavior of Epoxy/alumina Spacers

Gas-insulated transmission lines (GIL) have many advantages such as small footprint, large transmission power, good electrical performance, and compact structure, and are increasingly used in the field of long-distance transmission. At the same time, in a gas-solid composite insulation system, a large amount of electric charges accumulates on the area of the insulator under a long-term DC voltage, which will distort the creeping electric field, and then trigger creeping discharge. Surface charge accumulation on insulators becomes an important bottleneck to restrain the development of DC energy transmission system. Scholars have carried out a lot of work, but the practical application of many methods is still a problem. The surface coating is simple to prepare and easy to implement. Therefore, it is of great engineering significance to study the effect of surface coating on the charge accumulation. This paper uses active electrostatic probes and surface charge inversion algorithms to calculate the surface charge distribution with different SiC content and particle size coatings. Based on the analysis of the surface charge accumulation characteristics on the SiC/epoxy coated insulators, it's found that SiC coatings exhibit non-linear conductivity characteristics only in insulator samples with higher content and smaller particle size. With SiC content increasing and particle size decreasing, the surface charge accumulation has a clear tendency to saturate, and the surface charge dissipation rate increases. Under high external electric field, carriers in coatings produce tunneling effects and thermal transitions. This process accelerates the surface charge migration, significantly inhibiting surface charges accumulation, accelerates dissipation of surface charges and enhancing the electrical strength of the insulator. The results can provide a feasible reference for the design and optimization of DC GIL.