Parameter determination method for model of ZnO varistors based on dynamic V-I characteristics

Abstract

This study investigates the dynamic volt-ampere characteristics and residual voltage responses of ZnO varistor of five different sizes under various impulse waveforms, including 8/20 μs lightning current, 30/80 μs operating wave, 1/5 μs steep wave, and 2 ms square wave impulses. The experimental results demonstrate that larger ZnO varistor exhibit a downward shift in the dynamic volt-ampere characteristic curve. The IEEE frequency-dependent model was used in simulations to evaluate its applicability to different waveforms. For 8/20 μs and 30/80 μs impulses, the model yielded simulation errors within 5 %, while for 1/5 μs and square wave impulses, the errors were approximately 10 %. Significant discrepancies were observed between the experimentally measured and simulated energy absorption values, indicating the IEEE model's limitations in accurately representing such waveforms. To address this, the circuit structure and nonlinear resistance parameters in the IEEE model were revised based on experimental dynamic volt-ampere data. The resulting improved simulation model reduced the average simulation errors for residual voltage to within 4 % for the four waveforms especially for the three waveforms of 8/20 μs, 30/80 μs and 1/5 μs, the errors are within 2 % and for energy absorption to within 4 % across all tested varistor sizes and waveforms. These results confirm the enhanced accuracy and applicability of the improved model for simulating both residual voltage and energy absorption. The value of nonlinear resistance in the model has been clearly defined and can be obtained from experimental results.