# Impulse Breakdown Characteristics and Cost/Benefit Analysis of $SF_6/CCL_2F_2/C0_2$ Mixtures

Raghavender, D and Naidu, MS (1989) Impulse Breakdown Characteristics and Cost/Benefit Analysis of $SF_6/CCL_2F_2/C0_2$ Mixtures. In: Conference on Electrical Insulation and Dielectric Phenomena, 1989. Annual Report, 29th October-2nd November, Leesburg,VA, pp. 489-494.

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A comprehensive study has been carried out in $SF_6/CCL_2F_2/C0_2$ mixtures to measure 50% breakdown voltages $(V_5_0)$ using both positive and negative polarity lightning impulse (1.2/50 $\mu$s) voltages under non-uniform fields (5 mm. rod – 230 mm plane electrode) over a pressure range of 0.1 to 0.5 HPa for a gap spacing of 20 mm. The sum of $SF_6$,and $CCL_2F_2$ concentrations in the mixture was always maintained in the range of 21 to 40%, rest being $CO_2$. Among the different sets of $SF_6/CCL_2F_2/CO_2$ mixtures studied, two ternary mixtures, namely 20% $SF_6/20% CCL_2F_2/60% CO2$ and 30% $SF_6/10% CCL_2F_2/60% CO_2$ are found superior to $SF_6$. From the known gas content in the mixtures and from the measured breakdown voltages a cost/benefit analysis has been carried out for the various mixtures investigated. A striking feature of this analysis is that the most promising ternary gas mixture, namely, 30% $SF_6/10% CCL_2F_2/60% CO_2$, costs only 33% of the cost of pure $SF_6$, giving 110% to 130% positive breakdown strength, and 90 to 100% negative breakdown strength as compared to that of pure $SF_6$.