AC Breakdown Characteristics of Air Insulated Sphere-Plane Gaps with Glass Barriers

The experimental studies and theoretical analysis of the effect of glass barriers on AC breakdown characteristics of sphere-plane gaps are presented. Barriers made of three different glass materials were initially tested at different positions in a fixed sphere-plane gap. Then silicate glass barriers of various sizes were selected for further tests in different electrode arrangements, where the radius of the sphere varied between 0.5 cm and 2 cm and the gap distance ranged from 2 cm to 5 cm while the distance from the barrier surface to the sphere tip was fixed. The obtained results indicated that the barrier effect was most significant in the arrangement with the smallest radius of sphere electrode, longest gap distance and barriers of large sizes and led to an increase of breakdown voltages. The highest voltages, up to 205% of that of pure air gap, were obtained for configurations providing small field utilizations factors, which were evaluated from the results of electric field calculations. The relationship between the breakdown voltage levels and the discharge breakdown paths is discussed.