Dielectric strength of SF<inf>6</inf> in a non-uniform field

Abstract

This paper presents some of the anomalies in the dielectric strength of SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> as a function of pressure and electrode separation in a non-uniform field. Over certain pressure ranges the a.c. voltage breakdown gradient may remain nearly constant or even increase with increasing electrode spacing rather than decreasing as normally expected. This yields unexpectedly high breakdown strength, characterized by the presence of corona before sparkover. This was termed “Corona Stabilized” breakdown in a recent paper by Camilli, Gordon, and Plump. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(1)</sup> This phenomenon will be discussed in view of the relation to be shown to exist between the d.c. and a.c. dielectric strength of SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> and the effect of electrode spacing on the position of the maximum which occurs in the curve of dielectric strength vs. gas pressure. The positive and negative d.c., 60 cycle, and -impulse dielectric strengths as a function of pressure for a given electrode configuration is also illustrated and this information used to indicate the time required for corona stabilization to take place.