When the DC power supply system suffers from overload and short circuit

etc.

it requires that the DC fast switch can not refuse action or act abnormally

especially can not do the overstep action

otherwise the accident range will be expanded. This paper mainly discusses the characteristics of current-time and differential coordination of DC power supply system in substation

discusses the problems of the protection configuration and differential coordination of the upper and lower DC fast switch used in the operation field

and studies the making of a kind of DC fast switch differential coordination testing device which provides a research tool for design selection and maintenance inspection for the future DC fast switch in the substation.