Comparison of swarm and breakdown data in mixtures of nitrogen, carbon dioxide, argon and oxygen

Abstract

Mixtures of atmospheric gases such as , , and Ar are seen as possible insulation gases in high-voltage equipment, both with and without the admixture of a fluorinated gas such as the C4F7N nitrile or C5F10O ketone. Therefore, the binary gas mixtures –, – and –, as well as some selected ternary gas mixtures, were measured with a pulsed Townsend experiment and a breakdown experiment. In order to compare the experimental results, the breakdown voltage was estimated applying the streamer criterion to the effective ionization coefficient obtained with a pulsed Townsend experiment. The comparison shows a very good agreement between the two methods, which implies that it is possible to predict the electric strength of atmospheric gases in homogeneous electric fields over a wide pd range (product of vessel pressure p and electrode gap separation d) from swarm parameters only. Our results show that an admixture of 5% to – mixtures increases the breakdown voltage by 1%–2% in the measured pd range compared to the basis gas mixture. –– mixtures with an concentration between 40% and 80% and 5% of show an increased breakdown strength of around 8% compared to synthetic air (i.e. – 80%:20%) without .