A study of alternative insulating gases to SF₆

Abstract

Impulse breakdown of a point/plane gap in mixtures of SF 6 with selected buffer gases (air, CO 2 and N 2 ) has been studied. It has been found that the minimum impulse breakdown voltage of these SF 6 mixtures can be higher than or comparable with that of pure SF 6 . This finding is discussed in terms of the change of ion mobility and ionization energy in the mixtures. Some degree of immunity from the breakdown initiated by filamentary conducting particles in the system was observed using the mixtures.

Negative Corona Current Pulses in SF6– Air Mixtures

“…However, SF 6 is also efficient infrared absorber, and because of its chemical inertness is not rapidly removed from the earth's atmosphere, which make SF 6 potent greenhouse gas [1]. Therefore SF 6 presents an urgent environmental concern and the research of alternative insulating gases of greater environmental friendliness is of considerable interest [2].…”

“…An additional disadvantage of SF 6 insulation is that the insulation performance of SF 6 is limited not by its uniform dielectric strength, but by the effects of local field enhancement due to either roughness of the stressed surfaces or the unwanted presence of conducting particulate contamination leading to the formation of corona discharges [2,3]. For example, it is generally accepted that in a common electrode geometry (uniform or quasi-uniform fields) the criteria for projection-initiated breakdown of a high-pressure SF 6 insulation may be usually interpreted as the negative corona-onset voltage [4,5].…”

“…There are clear indications that certain mixtures, as for example mixtures of SF 6 with dry air [2,3], might have advantages over SF 6 in the non-uniform field conditions. Nevertheless, it is apparent that accurate predictions of their properties require more information on electrical discharge phenomena in the non-uniform field conditions, particularly on negative corona formation.…”

Negative corona discharge in the mixture of nitrogen with SF6

“…It is known [1] that the insulation performance of SF 6 is limited, not by its uniform dielectric strength, but by the effects of local field enhancement leading to the formation of corona discharges. As a consequence, the practical requirement is not necessarily for a gas with superior uniform field dielectric strength, but rather for an SF 6 -based gas mixture with an improved dielectric strength under the non-uniform field conditions associated usually with the presence of corona discharges.…”

Lightning Impulse Breakdown Characteristic of Dry-Air/Silicone Rubber Hybrid Insulation in Rod-Plane Electrode

“…SF 6 /CO 2 mixture gas has been reported to have more excellent insulation characteristics than SF 6 /N 2 mixture gas [11][12][13]. Also in non-uniform electric field, SF 6 /air and SF 6 /CO 2 mixture gas showed a higher breakdown strength than breakdown strength of SF 6 gas and by addition of 1% CO 2 in 50% SF 6 / N 2 gas mixture, breakdown strength has been reported to be more increased than breakdown strength of SF 6 /N 2 and SF 6 respectively 1.31 and 1.15 times [14][15].…”