Development of metal oxide varistor element for power systems

A highly nonlinear arrester can improve the insulation coordination of electrical substations and reduce the basic impulse level of power systems. Metal oxide varistors with zinc oxide as one of their constituents are used as advanced protective devices for power systems against transient overvoltages. A number of compositions of zinc oxide have been reported. This paper investigates ZBS (zinc oxide, bismuth oxide, antimony oxide) compositions together with the addition of magnesium oxide. The compositions were sintered for two hours at three different temperatures 1200°C, 1225°C and 1250°C. Sintered bulk densities as high as 95% were achieved. Their electric field versus current density (E-J) relation was found to be highly nonlinear. The paper includes a study of the sintered pellet using standard impulse voltage testing and microstructural analysis