Performance comparison of varistor models under high current derivative impulses

Surge protective devices (SPD) testing procedures are mainly performed with standard current pulse types. However, none of these standard current waveforms reproduce the very fast rise time and the large peak current derivatives observed in subsequent return strokes. In the literature there are several mathematical models to represent metal oxide varistor that have been developed based on standard impulse conditions. These models are being used routinely in the analysis of the various electronic circuits under transient conditions. In this paper, a study was conducted to have a performance comparison between the two varistor models, simplified varistor model and Durbak's model, available in the literature under high current derivative impulses. The experiments and simulations were performed on disk type varistors with different diameter sizes, i.e., 20mm, 10mm, and 05mm with nominal operating voltage of 230 V. The Roman Generator developed at Uppsala University was used as the high current derivative impulse generator which can produce a peak current up to 1500 A with 10 ns rise time and its rate-of-rise is in the order of 1011 A/s. The results showed that for standard 8/20 ěs lightning impulses, simulation results of these models had a good agreement with the experimental data. However, these two models need to be improving in order to improve their performance under high current derivative impulses into the sub-microsecond range