Investigation of corona on wires and points in sulfur hexafluoride

The negative corona extinction voltage or breakdown extinction voltage has been determined in air and SF₆ at atmospheric pressure for the sphere to plane configuration. Spheres or points ranging in size from a 0.250" radius sphere to a 0.0024" radius phonograph needle were used with gaps of the order of 1-10 millimeters. The negative corona extinction voltage was also determined for the coaxial cylinder configuration in air and SF₆ at atmospheric pressure for inner cylinders ranging in radius from 0.050" to 0.0012" and an outer cylinder of 0.250" or 0.500" diameter. The corona or breakdown extinction field is calculated from the above data as a function of the radius. The ratio of the field at which corona starts in SF5 to the field at which corona starts in air decreases from about 2.4 to 1.4 as the field becomes more non-uniform. The smaller the radius of the electrode the nearer is the value of the SF5 corona field to that of the air corona field.