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

Abstract

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 highpower 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 (constantcapacitance) 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.