Approximate Mathematical Expressions for Nonlinear Resistive Properties of Zinc Oxide Elements

A zinc oxide (ZnO) varistor, also called a metal oxide varistor, has a resistance or resistivity that varies with the applied voltage or electric field. The nonlinear resistive properties of ZnO elements are usually obtained experimentally as the voltage versus current characteristics. It is shown that a simple mathematical expression with four adjustable constants can well reproduce measured nonlinear resistive properties of six low-voltage ZnO elements.