Current distribution in MOV element stressed by 4/10 μs impulse current

Abstract

This study focuses on current distribution in a metal oxide varistor (MOV) element stressed by 4/10 μs impulse current studied using the finite-difference time-domain (FDTD) method. After 100 kA shots, V 1mA/ mm values, which indicate deterioration of nonlinear characteristics of MOV, in edge parts of MOV elements decreased more than those in center parts. FDTD analysis was conducted in two ways, namely 1-D and 3-D models. The varistor is represented with many nonlinear cubic cells of 3 mm × 3 mm 0× 3 mm It turns out from the 3-D FDTD analyses that the skin effect is insignificant for a lightning current having a rise time of 4 μs. However, if there is small difference in the nonlinear characteristic of a ZnO element between its periphery and other parts, the distributions of current density are considerably affected, which may result in enhanced degradation of a varistor element in its periphery.