Analysis of the Dielectric Breakdown Characteristics for a 252-kV Gas Circuit Breaker

A study was carried out on the characteristics of the dielectric strength of gaseous working medium in a puffer circuit breaker following current interruption. A reduced critical electric field strength (E/N)(cr) was defined. Its value for SF6 gas within the temperature range of 300 to 3000 K and pressure range of 1 to 32 atm was obtained by solving the Boltzmann equation with most recent atomic data, which allows the determination of the critical electric field strength E-cr at different temperature and pressure. The dielectric behavioral pattern of the breaker was then characterized by applying the E-cr data to the temperature and pressure fields obtained by a 2-D magneto-hydro-dynamics model encompassing all important mechanisms operating in the arcing process. The E-cr distribution at 80 and 110 mu s after current zero was then compared to the electric-field distribution to arrive at important information regarding the weakest point or regions in the design. Using a standard rate of rise of recovery voltage profile, the critical dielectric withstand level of the breaker was also predicted.