Partial Incorporation of Nonlinear Resistive Field Grading Materials: A Strategy for Enhanced Field Reduction and Safety

Abstract

In this study, we fabricate, characterize, and apply nonlinear resistive field grading (NLRFG) materials in vacuum recloser, cable joint, and outdoor cable termination models. The NLRFG materials are fabricated by dispersing various sizes and loadings of zinc oxide (ZnO) nanofillers in polymer matrices including epoxy resin and silicone rubber. The nonlinearly varying resistivity of these materials is characterized by measuring <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> curves. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> characteristics of the NLRFG materials are modeled and incorporated into a finite element analysis (FEA) platform. The electric field reducing the performance of the fabricated NLRFG composites is analyzed in FEA based on the actual designs of vacuum recloser, cable joint, and outdoor cable termination. Three different case studies are reported: 1) where regular epoxy or regular silicone rubber is used; 2) where NLRFG materials are used; and 3) where NLRFG materials are partially incorporated. The results suggest that 37%, 27%, and 29% reductions in the local maximum electric field are achieved when NLRFG materials are used in the vacuum recloser, cable joint, and outdoor cable termination, respectively. Power loss caused by leakage current in these models is also analyzed. The findings imply that the partial implementation of NLRFG materials not only could be more effective in terms of electric stress reduction but more safe than the full incorporation of them as it prohibits the formation of conductive paths across high-voltage and ground during overvoltage transients that can be caused by lightning strikes.