Investigation into the equivalent circuit of MOV and the determination of its parameters

The Metal Oxide Varistor (MOV) has been widely utilized in the power industry due to its high degree of nonlinearity and excellent capability of carrying a large amount of electrical current. Though studies have been conducted to understand the current response of the MOV to step voltages qualitatively, modeling the current-step voltage relationship of the MOV quantitatively has never been reported. This paper presents the investigation into the current responses of the MOV to step voltages with different amplitudes. An equivalent circuit representing the MOV in the whole current region and a method for determining its corresponding circuit parameters are proposed based on the fact that the MOV shows polarized current in the low current region and displays conducting delay effect in the heavy current region. Also in the paper, the current response curves of the MOV under different step voltages are analyzed theoretically and experimentally. In order to obtain the dynamic resistance and the dynamic inductance, the current response curve is formulized quantitatively using the exponential equation when the step voltage is small and a diagrammatizing method is adopted when the step voltage is large. The authors discovered that the equivalent circuit of MOV mainly consisted of four branches: the capacitance branch, two polarized branches (fast-polarized branch and slow-polarized branch), and the nonlinear conducting delay branch.