Research On The Pulse Degradation And Destruction Mechanisms Of Zinc Oxide Varistors With Double-pulse Current

Multiple stroke lightning ground flashes can impose surges of exceptional severity on the arresters used in overvoltage protection. Repeated strike experiments on zinc oxide varistors show that, under double-pulse current, degradation and destruction happen easily. The shorter the interval between the two pulses of the current wave, the fewer strikes the varistors can endure. At the same time, the DC LJImA changes fast-slowly-fast alone with the experiment continuing.Microstructual disorder, such as variations in the height of the electrostatic potential at grain boundaries and electrode protrusions into the zinc oxide varistors, causes substantial temperature rise in a microscopic region around the defect and is the source for failure. To analysis the principle of degradation and destruction, a reasonable relationship between the electrostatic potential and 1-V characteristic parameters is raised; a computation model for electron trap effect is originally proposed, which leads to a conception of critical trap electron density. This paper also suggests that ion migration increase the resistance of the varistors in middle and high voltage, so the varistors can endure some strikes before failure. Based on those new ideas, simulative computation in two kinds of models interprets the experimental data and phenomena.Hopefully, the results obtained from this paper would prompt the further research of the degradation and destruction mechanisms of zinc oxide varistors under multipulse current strike, and offer suggestion on revising the lightning test standards and improving the product quality of zinc oxide varistors, etc.