V-t characteristics with a time span of 1-1000 μ sec were measured for vacuum gaps in order to identify the influence of electrode arrangement and gap length on V-t characteristics of vacuum gaps. Plate to plate, ring to plate and sphere to plate gaps with distances of 1-12mm were used for the measurements. As a result, the following points were observed.
(a) Plate to plate gaps:
(1) When the gap length is less than approximately 1mm, breakdown voltage is independent of breakdown time.
(2) When the gap length is more than approximately 1mm, the breakdown voltage decreases with increases in breakdown time.
(3) AC breakdown voltage is 70-80% of 1.15/3.8msec switching impulse breakdown voltage. DC breakdown voltage is almost the same as the AC. The impulse ratio between 1.2/50 μ sec lightning impulse breakdown voltage and the AC is 1.25.
(b) Ring to plate and sphere to plate gaps:
(4) Under positive voltage applications, behaviour of V-t characteristics in the plate to plate gaps of less than d=1mm was observed. This feature was identified under all the gap length.
(5) Under negative voltage applications, behaviour of both points (1) and (2) above was observed. Critical gap length where the behaviour changed from point (1) to (2) depended on the radial curvature of high voltage electrodes.
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