The author describes the performance of metal-oxide varistors asapplied to dynamic insulation of high-voltage power systems. Amathematical model for a dynamic insulator is constructed, which takesinto consideration the effects of the surface contamination conditionsas well as the arc development and propagation on the flashover behaviorof outdoor insulators. The nonlinear I-Vcharacteristics of metal-oxide elements are utilized to both suppresssystem overvoltages and improve the flashover performance of theseinsulators. A method for designing the optimum configuration (i.e. theone that corresponds to best transient and flashover performance) ofmetal-oxide units of given characteristics is developed. Experimentaldata of zinc-oxide varistors are used to illustrate the designprocedure. It is shown that the optimum zinc-oxide configuration dependsmainly on the system voltage level, geometry of the insulating surface,and atmospheric contamination level. The new design procedure is used todevelop a simple dynamic insulator unit resulting in an improvement ofover 14% in the flashover performance under uniform contaminationconditions. The concept of manufacturing solid insulator units withbuilt-in dynamic insulation properties is suggested
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