The Impact of Electric Field Treatment on Nonlinear Conductivity of Tetra-needle-shaped ZnO Whisker/Carbon Fiber/Liquid Silicone Rubber Composites

Nonlinear electrically conductive composites are widely used for electric field grading in HVDC systems. However, the composites prepared using current methods can rarely simultaneously meet the requirements of a high nonlinear coefficient, low switching field and low filler content, which limits their application scope. In this study, by applying a 10-kHz AC electric field during preparation, the prepared tetra-needle-shaped ZnO whisker/carbon fiber/liquid silicone rubber (T-ZnOw/CF/LSR) composites can be implemented in a manner to meet the above three requirements. The electric field-assisted LSR composites filled with 20 phr T-ZnOw and 5 phr CF can have a switching field as low as 420 V/mm and a nonlinear coefficient up to 11.7. The mechanism for the electric field-assisted enhancement of the nonlinear characteristics of the T-ZnOw/CF/LSR ternary hybrid system is explained based on the electromechanics of the suspended particles. The nonlinear characteristics and the filler content do not present a positive correlation, and a low (< 10 phr) or high (> 30 phr) filler content leads to decreased nonlinear characteristics in the composites. Compared with LSR, the electric field-assisted composites introduce a large number of shallow traps with increased trap density and reduced trap energy levels.