Development of advanced built-in surge arresters for distribution system with new zinc-oxide elements

New zinc–oxide elements with a varistor voltage about twice that of conventional ones have been developed by reducing the ZnO grain size with a new additive, which enables to halve the series number of elements in metal oxide surge arrester. Using these elements, we have developed advanced built-in surge arresters enclosed in 6.6 kV pole transformers and switchgear. The advanced arresters have been reduced in volume by 25% compared with conventional ones. This paper describes the specification and construction of the advanced arresters and the results of various evaluation tests.