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 Ecr at different temperature and pressure. The dielectric behavioral pattern of the breaker was then characterized by applying the Ecr 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 Ecr distribution at 80 and 110 μs 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.