An optimal surge arrester for EHV air insulated stations utilizing high-gradient MO resistors

The use of high-gradient (HGR) MO resistors makes it possible to significantly reduce the length of surge arresters for air insulated substations (AIS). The optimal length would be to use HGR MO resistors which exactly fill up the necessary length needed to obtain a sufficient margin between arrester protection level and the voltage withstand of the housing. However, this would require a design with excellent thermal properties which could handle the increased power losses per unit length and higher temperature after energy absorption. This paper describes a surge arrester design in accordance with this concept. Furthermore, the requirements, type tests performed to verify the design and experience from a three and a half year field installation with supervision of the arrester leakage current are presented.