Further experiments in high current switching using small contact gaps

Previously, a series of tests were performed on two types of commercial vacuum interrupters, herein called type A and Type B, to ascertain the effect of the contact gap on their high current interruption ability. These tests are a continuation of the earlier series, intended to test hypotheses concerning the results seen. For all tests, three interrupters of each type were tested at reduced contact gaps. The first series consisted of gaps between 8 mm and 1 mm. This work has now been extended to include gaps of 1 mm to 0.25 mm. In addition, identical contacts were subjected to short circuit testing in a vacuum demountable chamber which allowed filming of the arc by means of a high speed camera. The earlier results indicated that one type, Type A, showed a significant reduction in the probability of interruption of the rated short circuit current at contact gaps below 4 mm, whereas the other type, Type B, showed no degradation at contact gaps down to 1 mm. The new work confirmed this showing that Type B only showed significant degradation in performance at gaps of 0.5 mm and below. The reasons for this are discussed