Results of outdoor ageing of cast epoxide systems under electrical stress

Insulators used outdoors have to have long creepage paths, which are substantially longer than the insulator itself. Sheds provide this long path and also form water shedding points to hinder cascade effects in conditions of heavy rain. This form of insulation is well established with porcelain insulators in vertical and U string configurations. Protected creepage paths are provided, and in fact required in many specifications, but it is not established that a protected path is desirable with polymer insulators. Gepol^1–4 uses a suspension set with a protected path whereas the systems developed in England do not.^{5, 6}