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The usage of medium‐voltage switchgear is more and more common in high altitude areas. Few relative standards about the selection of switchgear air gap in low air pressure conditions are currently available for referring. In this study, four different types of switchgear air gaps, as well as a typical rod‐plane gap, are taken as the samples, and their positive and negative lightning strike discharge characteristics under low air pressure are tested in the artificial climate chamber. The effects of the electrode structure, polarity, air pressure, humidity, and gap distance on the discharge performances are analysed as well. Research results indicate that the four switchgear air gaps and typical rod‐plane gap differs greatly in lightning impulse discharge performances and polarity effects. In low air pressure conditions, the lightning impulse breakdown voltage of either positive or negative polarity can be corrected by U50 = U50,0 × (P/P0)n. The discharge voltage under positive lightning impulse is more easily affected by air pressure than that under negative lightning impulse. Atmosphere humidity will cause dispersiveness of air‐gap lightning impulse discharge voltage, which performs to be non‐linear with a gap distance lower under 400 mm. Research results are referable for the design, selection and installation of medium‐voltage switchgear in high altitude areas. [ABSTRACT FROM AUTHOR]

The bare conductor in switchgear constitutes complicated air gaps, and their AC withstand characteristic will obviously affect switchgear insulation performance. In this paper, AC withstand tests of various types of air gap were carried out. The air gap samples were rod-plane air gap and 4 typical types of air gap from the bus chamber of 40.5 kV metal-enclosed switchgear. The samples were tested in climate chamber where high altitude environment was simulated. And correction of withstand voltage for switchgear air gaps at low air pressure were conducted. Test results indicate that, the withstand characteristic of 4 typical types of air gap in switchgear are different from that of rod-plane air gap. The relationship between withstand voltage Uw and air gap distance d is nonlinear. The influencing characteristic exponent n of air pressure on Uw is related with air gap type. Linearity value m and air pressure index n are independent to some degree. An equation was proposed to express the relationship of Uw with air gap distance d and altitude H, and this equation can be used to calculate the safety distance of air gaps in switchgear under low air pressure situations. The results are significant for the design and selection of switch devices. [ABSTRACT FROM PUBLISHER]