Measurements of Breakdown Potential and Ionization and Attachment in SF6-CO2 Mixtures

The swarm coefficients (ionization and attachment coefficient) and sparking potentials have been measured in SF6-CO2 mixtures over the range of 60¿E/P¿110 V/mPa and gas pressures varying between 0.7 and 75 Pa, gap spacings between 2 and 40 mm. The limiting values of E/P, (E/P)lim, were obtained by three methods: measuring E/P as a function of Pd; computing (¿-¿)/P as a function of E/P; and Debitetto-Fisher criterion. The rate of increase of the attachment coefficient with increasing percentage of SF6 in the mixtures was much larger than the rate of change of the first ionization coefficient. Addition of SF6 increased the sparking potential under uniform and non-uniform fields.