Nonlinear electrical conductivity and breakdown strength of PPy/BN/EPDM composites for cable accessory applications

Abstract

The rubber-based cable accessory always serves as the joints component for connecting two power cables due to the length limitation of a single cable, which plays a key role but possesses a high failure rate in high-voltage transmission engineering. Because the large mismatch of electrical parameters between the ethylene-propylene-diene monomer (EPDM) rubber and cross-linked polyethylene of cable main insulation induces the severe electric fields distortion at the stress cone that threatens the safe operation of cable accessory. To develop the rubber materials with excellent nonlinear conductivity property is a favorable technique to relieve the electric field concentration in cable accessory. Different from previous studies, this work utilizes organic conductive polypyrrole (PPy) rather than inorganic conductive or semi-conductive fillers to induce nonlinear conductivity of EPDM. Meanwhile, the 10wt% hexagonal boron nitride (BN) is also incorporated into EPDM for reconciling the breakdown strength of the composites according to our previous studies. The results show that incorporating PPy organic filler can induce nonlinear conductivity characteristics of the PPy/BN/EPDM composites, which become more significant with the increase of PPy doping content. At 30 °C, 50 °C, and 70 °C, the nonlinear coefficient of 5wt%PPy/BN/EPDM is increased by 36.4%, 29.9%, and 47.7% compared to 1wt%PPy/BN/EPDM, and the threshold field strength is reduced by 44.7%, 46.66%, and 37.7%, respectively. The COMSOL Multiphysics field simulation results show that using PPy/BN/EPDM composites as enhanced insulation can relieve the electric field concentration especially at the root of the stress cone, guaranteeing the safe operation of the cable accessories in the electric transmission.