Analysis of ceramic varistor

The frequency characteristics of the capacity and the dissipation factor of a ceramic ring varistor have been measured in the range from 10 kHz to 1 MHz. From the measurements, the equivalent circuit was determined, considering the internal structure of the ceramic ring varistor. The equivalent circuit contains three blocks, the grain boundary layer, the depletion layer, and the conduction layer. At the block of the conduction layer, only resistance is assumed, and at other blocks resistance and capacitance are assumed. The resistance and the capacitance of each block are 15 Ω and 6 nF, 10 Ω and 65 nF, and 0.5 Ω, respectively. Using the present equivalent circuit, transient phenomena have been studied. It is found that the decay time of the damped oscillation wave caused by RLC resonance can be controlled by the inductance and the winding resistance of a motor. It is also found that the period of the damped oscillation wave can be controlled by the resistance and the capacitance of the ceramic varistor