ZN12 (ZN72) -40.5 Indoor Vacuum Circuit Breaker 35KV three-phase AC 50HZ applied to power system, the circuit breaker for the ceramic structure, using the longitudinal magnetic field contacts, is small, the proliferation of breaking arc generated when current distribution in the contact on the same local melting phenomenon does not occur, but also has a low arc energy voltage (20-200V) and low chopping current (4-5A), and operate with high reliability organizations.