Damage Mechanism Analysis of ZnO Varistor Under Multi-Pulse Lightning Current Experiment

Recent studies indicate that multi-pulse lightning currents from multiple lightning stroke significantly damage and fail zinc oxide (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{Z n O}$</tex>) varistors. This study investigates the thermal behavior and damage mechanisms of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{Z n O}$</tex> varistors under two types of multi-pulse surge currents: equal amplitude and non-equal amplitude pulses. Experiments used <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$8 / 20 \mu ~\mathrm{s}$</tex> surge current (per IEC 62305-1:2010) with inter-pulse intervals following T/ASC 6004-2022 and T/CMSA 0032-2022. For equal amplitude pulses, increasing the number of pulses elevated the varistor's non-uniform surface temperature difference. For non-equal amplitude pulses, the maximum surface temperature of the varistor was linearly correlated with the absorbed energy. Increasing the number of pulses or surge current amplitude had equivalent adiabatic heating effects on temperature rising. Notably, the maximum surface temperature was more sensitive to the number of pulses than to surge current amplitude. It rose linearly under single-pulse conditions but exhibited a nonlinear inflection point under multi-pulse conditions, particularly for non-equal amplitude pulses, where the inflection point for abrupt temperature rising shifted earlier with increasing surge current. These findings reveal significant differences in damage mechanisms between multi-pulse and single-pulse surges, particularly in local temperature rise rates and uniformity, emphasizing the need to improve multi-pulse counting methods for voltage-limiting surge protective devices (SPDs) and refine protection standards.