Approach and basic evaluation for the DC circuit breaker with fault current limiting feature

The future electricity grid for the electric power distribution network is slowly moving in the direction of dc transmission. In order to prevent the fault propagation, provide protection against overload and fault, and isolate the faulty load in a dc power network, an overcurrent protection device must be applied to the switch gear for electric power management and control of the systems. Overcurrent protection devises such as electromechanical circuit breaker in the primary and secondary distribution systems protect all branch circuits on the load side of the discharge bus. This type of circuit breaker has the conflicting of time delay characteristics that trip delays must be long enough to open the circuit when a real fault exists. It should cause nuisance tripping. We are developing a solid state type of power switching device as a new power device for dc power network instead of electromechanical circuit breaker. The candidate for these switching devices should be Power MOSFET, IGBT, and SiC MOSFET. The environment of development of dc grids protection new power devices are now improved. Focusing on the application for the low and medium voltage dc grid, fast-acting switching function and current limiting features are brought up the idea to apply Si Power MOSFET, IGBT, and SiC MOSFET to the dc circuit breaker. The very basic evaluation for this fast-acting switching and current limiting function for the dc circuit breaker are shown by experiment in this paper. Our prototype switching device will open within 20 μs and we can freely adjust this elapsed time and fault current rating. To avoid nuisance tripping, we successfully performed current limiting function by extend the elapsed time using same control circuit.