New technology for medium voltage solid insulated switchgear

This paper describes epoxy casting, insulation and operating mechanism technologies applied to newly developed solid insulated switchgear (SIS). The main insulating material is epoxy resin of high toughness and high thermal-resistance. This resin increases mechanical and electrical strength, and enables the vacuum interrupter to be cast directly. Since movable parts of a vacuum circuit breaker and a vacuum disconnecting switch can not be insulated with solid insulation, composite insulation is applied to these part. This composition enables the insulating distance at atmospheric pressure in air to be decreased. For the operation mechanism, we developed a balanced magnetic actuator (BMA) with a permanent magnet and a solenoid coil. The BMA has characteristics such as low operating current, fewer parts and high reliability. With these new technologies, we have developed enclosed solid insulated switchgear of medium voltage class without SF₆ gas.