Erosion of metal enclosure due to electric arc was investigated to clarify the effect of the usage of different gas for internal arc tests in high-voltage switchgear. Since SF6 gas, which is commonly used in the high-voltage switchgear, has a potential to give negative impact on the environment, alternative testing using Air has been in discussion worldwide. Erosion characteristics of the metal enclosure due to the internal arc is crucial to establish test method with Air which gives equivalent test results to the testing with SF6.

Experimental investigation of the internal arc is conducted with different insulating gases (SF6 and Air) and different enclosure materials. Comparison of visual inspection, geometrical analysis, elementary analysis and cross-sectional observation indicate that erosion of enclosure is caused by the following two steps and predominant factor.

(i) Melting of metal enclosure

・In Air, energy injected by the heat transfer from the arc affects the amount of the molten metal.

・In SF6, chemical reaction energy on the metal affects the amount of the molten metal.

(ii) Spattering of molten metal

Impact pressure of the arc jet affects the spattering degree on the enclosure. The pressure depends on the arc diameter.