Lightning and switching impulse breakdown of rod/plane gaps in nitrogen and nitrogen/freon (CCl2F2) mixtures

Lightning impuse (1.2/50 ¿¿s) and switching impulse (200/200 ¿¿s) breakdown phenomena in nitrogen and nitrogen/freon mixtures have been investigated for rod/plane gaps at total pressures up to 5 bar and spacings up to 100 mm with freon concentrations varying from 1 to 20% in the mixture. Results of breakdown voltages show that, in general, substantial improvement in breakdown strength can be achieved, particularly for negative polarities with the addition of small percentages (¿¿ a few per cent) of CCl2F2 to N2. It is of interest to note that the characteristic `pressure effect¿¿ in the positive point breakdown voltage against pressure curve observed in many strongly attaching gases is ill defined in these mixtures, and can be seen only over a limited range of experimental conditions. The corresponding effect for negative point breakdown is observed in these mixtures at the relatively low pressures of 2 to 4 bar for long gaps (>40 mm). The breakdown voltages for a 100 mm gap with the switching impulse at pressures greater than 2 bar are generally 20% lower than the corresponding lightning impulse data.