Application of insulators to withstand switching surges in substations. I. Switching impulse insulation strength

When surge arresters are used to protect against switching surges (SS), the dimensions of the self-restoring and non-self-restoring insulation are determined by the protective level of the arresters. If the surge arresters do not protect against SS, non-self-restoring insulation should withstand the maximum SS entering the substation with an appropriate margin, while the self-restoring insulation, generally consisting of air gaps, is dimensioned following the same methodology as for line insulation. The authors discuss the parameters that affect the SS dielectric strength of air gaps forming the external insulation of substations, both phase to phase and phase to ground