SF6 circuit breaker insulation system design can be of two kinds with gas gap or along the surfaces of solid dielectric. The discharge conditions of along the surfaces of solid dielectric differ significantly from the discharge conditions in the gas gap and it can be the main factor in determining the circuit breaker geometric dimensions. In operation, the insulation system must withstand the normalized AC voltage and normalized
overvoltages. Nowadays SF6 insulation has gained wide-spread acceptance in high-voltage units as internal insulation due to high physical-chemical and electrical characteristics. Therefore the demand arose for reliable and accurate calculation techniques for analysis of structures’ electric strength by main gaps. However, presently
available criteria are frequently empirical or semi-empirical and application – specific, consequently their application is limited . Therefore performance evaluation of construction under high-voltage is complicated.