A comprehensive study of lightning impulse breakdown and cost/benefit analysis of ternary gas mixtures containing two electronegative gases

The ever increasing voltage levels in modern power transmission systems have stimulated considerable interest in the use of strongly attaching gases of high dielectric strength such as SF₆ and CCl₂F₂ as insulants. Because of the high cost of such gases, the economic considerations have necessitated research towards obtaining binary and ternary mixtures of these gases (SF₆ and CCl₂F₂) with unitary gases like N₂ , CO₂ and air, for practical applications. If a small quantity of SF₆ is added to N₂ or CO₂ in combination with a fluorocarbon gas such as CCl₂F₂ , this results in a considerable increase in the dielectric strength of the mixture at reduced cost. This paper discusses the lightning impulse (1.2/50 μs) breakdown characteristics obtained with different SF₆/CCl₂F₂/N₂ and SF₆/CCl₂F₂/CO₂ mixtures using 5 mm diameter rod-230 mm diameter plane electrode geometry over the pressure range of 0.1 to 0.5 MPa (1 to 5 bar) at a constant gap of 20 mm