vacuum circuit breaker(VCB) is high voltage outdoor switch gear with rated voltage 12kV, three-phase AC 50Hz, which is mainly used for making and breaking load current, over-current, short-current rural network, city network and miniature power system. The overall structure of this product is three-phase co-box type, three-phase vacuum explosion chamber in the metal box, the performance is reliable and insulation strength is higher by making use of SMC insulation material phase to phase insulation and to earthing.