729 / 2022-03-31 19:36:56

Surface charge behaviors of field grading nonlinear conductivity coatings

Surface charge,nonlinear condcutivity

Purpose/Aim

Nonlinear conductive materials, whose conductivity is dependent on the electric field, possess the ability of regulating electrical field distribution and inhibiting charge accumulation. However, influence of nonlinear construction methods and nonlinear parameters on the surface charging behaviors still need to be further investigated. To this end, this work presents surface charging and dissipating characteristics of epoxy/alumina specimens coated by different nonlinear composites (SiC and ZnO) materials.

Experimental/Modeling methods

Epoxy based composites containing different concentration of SiC or ZnO (10wt%, 20wt%, 30wt%,40wt% and 50wt%) were prepared by vacuum casting. Field-dependent I-V characteristics of specimens were measured at room temperature. Subsequently, these composites with known nonlinear coefficients were locally coated on the surface epoxy/alumina specimens to form a graded structure. Surface charging and dissipating of the graded structures under DC voltage were characterized systematically.

Results/discussion

The composites exhibit pronounced nonlinear behaviors with the increase of doping concentration for both ZnO and SiC fillers. With respect to the prepared insulation structure, charge accumulation on specimens with nonlinear coating have been significantly suppressed compared to the pristine specimen. As the amount of fillers doped in the coating increased, fewer charge accumulated on the surface, and the dissipation speed of accumulated charge accelerates. At the same doping concentration, ZnO coatings yield better charge suppression and improved charge dissipation ability compare with that of epoxy/SiC coatings.

Conclusions

Nonlinear conductance in the coating layer plays a crucial role in surface charge transport behaviors. In areas where surface charge accumulates, the volume resistivity of the coating decreases, which promotes the dissipation along the coating, thereby achieving a uniform surface charge distribution. Due to the higher nonlinear conductivity coefficient, composites with ZnO have an enhanced ability to suppress charge accumulation at higher electric field area.

Appendix (Figure, table, image…)