酸化亜鉛（ZnO）バリスタ素子内雷インパルス電流分布のFDTD解析

抄録

Distributions of transient electric field and current density in and around a metal oxide varistor, which has a diameter of 42mm and a thickness of 36mm, have been studied using the finite-difference time-domain (FDTD) method. The current injected into the varistor is a lightning impulse current having a peak of 100kA and a risetime of 4-µs. The varistor is represented with many nonlinear cubic cells of 3mm × 3mm × 3mm. The cell has a nonlinear resistivity—electric field characteristic in each of x, y and z directions, which is based on the measured nonlinear voltage—current characteristic. It follows from the FDTD analyses that the skin effect of the 42-mm-diameter varistor is insignificant for a lightning current having a rise time of 4-µs. However, if there is small difference of the nonlinear characteristic of ZnO element between its periphery and other parts, the distributions of electric field and current density are considerably affected, which may result in enhanced degradation or failure of the varistor.