The relevant technologies of the low-voltage circuit breaker are studied to solve protection problem in the active electric network. By controlling arc motion efficiently, the breaking capacity independent of polarity is improved to satisfy the protection demand of the PV generator system. By combining vacuum arc extinguishing technology and ACB operating mechanism, the breaking capacity of the circuit breaker is improved at the AC voltage range of 690-1149 V. And FEM analysis and optimization of operating mechanism are studied to increase the life of the breakers, which can fit protection demands in the wind turbine system. Based on directional ZSI (zone selective interlocking) technology, selective protection can be realized in the electric network with multi power sources. Application experience of the low voltage circuit breakers shows that above works can greatly ensure the operating security of the active electric network.