Development of high gradient zinc oxide nonlinear resistors and their application to surge arresters

Zinc oxide nonlinear resistors with double the conventional reference voltage gradient, while improving their protective characteristics and raising discharging capability, were developed and applied to tank-type surge arresters. On the basis of high-performance elements, which provide good protective characteristics, a simulation was performed on the relation between the composition of the raw material and the current-voltage (I-V) characteristics, consequently achieving a higher reference voltage gradient and an improved I-V nonlinearity. Moreover, the discharging capability was raised by improving the thermal distribution in the element when a current is applied and reducing their pores. This, when applied to surge arresters, permitted the number of elements, with the same diameter as conventional elements, to be halved. As a result, the number of parts, size, and weight of the surge arrester were reduced and its structure was simplified. A series of tank-type surge arresters using these elements for 66-550kV systems was developed, tested in various ways without problems, and applied in the field.