Recent topics of the medium-voltage switchgear in Japan

This paper introduces three items of newly developed 22 kV switchgear from Japan. These are: (1) switchgear with multifunctional vacuum interrupters, which enable significant downsizing through the use of a functional integration concept. The multi-functional vacuum interrupter integrates four functions (making, breaking, disconnecting, and grounding of the circuit) in a unit vacuum vessel. (2) A new type of air-insulated switchgear, which utilizes moderately compressed air and insulation barriers between the poles. Gas pressure dependence and barrier effect on the insulation is investigated experimentally. (3) Switchgear that uses solid insulation. All of the main-circuits, including vacuum interrupters, are molded by recyclable material. A composite insulation technique, using air and solids, is applied to movable parts, whose insulation ability is improved two or threefold over air alone. Finally, some basic research on vacuum insulation is introduced.