An Experimental Methodology for Modeling the Voltage-Dependent Capacitance and Resistance of Varistors: Implications on the Estimation of the Power and Energy Dissipation at Low Frequencies

In this work, a mathematical formulation is presented for estimating current conduction as well as power and energy dissipation in varistors. An experimental approach is introduced for time-domain modeling of varistors under AC voltages that considers their voltage-dependent capacitance and resistance. An application is made for 120 V zinc-oxide varistors stressed with AC voltages generated by a variable-frequency high-power supply; the voltage at the varistors' terminals is recorded along with the current for a low-frequency (60 Hz -1000 Hz) and amplitude (50 μA – 1 A) range. The predicted current conduction through ATP-EMTP simulations is in very good agreement with experimental records, in contrast to the simplified (constant-capacitance) modeling approach that underestimates power and energy dissipation. The effectiveness of the proposed macroscopic modeling approach in the low-frequency range is investigated with emphasis given to 400 Hz, commonly employed in aviation systems; the applicability of the proposed model in the high frequency and current range has been evaluated and discussed with the aid of impulse voltage and current experiments.