A study on the use of zinc oxide micro-varistor based field grading materials for composite line insulators

This paper examines the reduction in the electric field at the line end of a 230 kV composite suspension insulator that can be obtained by applying a field grading material (FGM) to the insulator core at the line end of the insulator. The FGM is based on a highly non-linear conductivity zinc oxide micro-varistor material; and COMSOL® Multiphysics version 5.6 at power frequency AC is used in the analysis. FGM of various nonlinearities and various lengths applied to the core is studied to determine the non-linear characteristics of the FGM and the length of application that provides the greatest reduction in the electric field. The results are compared to the same insulator fitted with a proper design of corona ring and the simulation results show that the corona ring can be eliminated by using the FGM.