An Experimental Study of Short-Circuit Current Making Operation of Air Medium-Voltage Load Break Switches

Abstract

Replacing SF 6 , the most potent greenhouse gas, with an alternative gas is a challenge faced by medium-voltage load break switches (MV-LBS). Air is a possible alternative, but there are some challenges regarding low dielectric strength leading to high arcing time and dissipated energy. Therefore, understanding the switching processes for both interruption and making operations in air MV-LBS is crucial to designing efficient compact switchgear. This work focuses on making operations in air MV-LBS. A synthetic test circuit and a model switch are designed based on the standards to simulate making operations under fault conditions similar to a real test. The test condition is set to achieve high pre-strike arcing time and energy. The results show that the most destructive impact of the making short-circuit current occurs in the first half-cycle of the load current when the pre-strike arc is formed. For an average short-circuit current with a peak of 22 kA and a breakdown voltage of 20 kV, the switch failed to re-open due to the arcing contacts welding after four successive making operations without main contacts and seven successive operations with main contacts. It has been shown that the total arcing contact mass loss occurs mainly during the pre-arcing time.Increasing the closing speed could be a possible solution to minimize the impact of arcing.