Composite insulation structure for medium voltage class switchgear

A Next generation medium voltage Cubicle type Vacuum Insulated Switchgear (C-VIS) has been to deliver high reliability for electric power systems. A composite insulation without SF6 gas is applied to the C-VIS, and realizes environmentally friendly system with compact equipment size. The movable electrode in the double-break three-position vacuum switch is connected to the vacuum and air insulating rods in series. The air insulating rod prevents an earth fault even if a vacuum leakage occurs. The combination of the air insulating rod and the vacuum leakage monitoring system contributes to improving reliability. The air insulating rod is electrically connected to the vacuum chamber of the double-break three-position vacuum switch. Hence, the air insulating rod was designed by clarifying the induced voltage of the vacuum chamber in actual operations, and the insulation performance was verified with enough margins.