An Approximate Mathematical Expression for Nonlinear Resistive Properties of Metal Oxide Varistor Elements for FDTD Simulations
Tokuya Tanaka, R. Tsuge, Yoshihiro Baba, Yoshimasa Tsujimoto, Naoyuki Tsukamoto
Abstract
A simple mathematical expression for nonlinear resistive properties of metal oxide varistor (MOV) elements is proposed for electromagnetic and surge simulations using the finite-difference time-domain (FDTD) method. The nonlinear resistive properties of MOV elements are obtained experimentally as the voltage versus current (V-I) characteristics. The V-I characteristics are converted to the resistivity versus electric field (ρ-E) characteristics. The ρ-E characteristics are approximated by the simple mathematical expression with three adjustable constants, the values of which can be easily determined with the least square method. The proposed simple ρ-E expression is of great use in FDTD simulations since it can approximate measured ρ-E characteristics reasonably well and requires no iterative computations.