Zinc oxide-praseodymium oxide elements for surge arrestors

Zinc oxide elements have been developed which contain praseodymium oxide rather than bismuth oxide as a principal additive component. These elements have been used to produce gapless surge arresters with rated voltage up to 360 kV. The two-phase microstructure of these elements increases the active area of grain boundaries, which is the origin of nonlinearity in the V-I relation. This increases the effective area of the electrodes, resulting in a higher apparent dielectric constant by a factor of 1.5 and a higher capability for short-wave front-discharge withstand. The absorption capability for long-duration discharge was improved by obtaining higher resistance at the peripheral of the element than at the inner area