Influence of electrode configuration upon electric breakdown in electronegative gases

Abstract

This paper represents an effort to derive a theoretical expression which will predict the influence of electrode configuration upon the electric breakdown voltage in electronegative gases. The initial portion of the paper is involved with a presentation and discussion of the generalized condition for breakdown in all gases for an unspecified electrode configuration or structure. The equation is then applied to the particular configuration consisting of two parallel wires of infinite length. An equation is derived, from which it is possible to calculate the breakdown voltage of any gas as a function of the radius of the wire r0. Knowledge of certain parameters, characteristic of a specific gas, is the only requirement necessary to accomplish this. The results of calculations are presented for the simple gas nitrogen, which does not have a tendency to produce negative ions by electron capture. These are compared with the results of similar calculations for the highly electronegative gas C3F8. The calculations show that the breakdown voltage of nitrogen is strongly dependent upon r0, which is in agreement with the experimental observations of previous investigators. C3F8, on the other hand, showed entirely different behavior. To be more specific, the value of r0 appeared to have little if any influence upon its breakdown voltage. Furthermore, it is shown that the electrode configuration, giving rise to distortion of the electric field, does not affect the final outcome of the calculations when the gas under consideration is highly electronegative. Experimental verification of this prediction has been achieved by measuring the breakdown voltage of C3F8 in a uniform electric field, and comparing the results with those obtained with the point-to-plane configuration. For both cases, the results agree to within 10%, providing adequate verification of the conclusions derived from the theory.