Aimed at the problem that the failure of electronic components or power off in the current control unit of a short-circuit current protection device will lead to a protection failure, a passive electromagnetic current transformer is proposed. The working principle for the trigger device is analyzed, and the maximum magnetic flux of iron core within the effective working range of the transformer is determined according to the magnetization curve of the core material. Considering that the magnetic flux in the iron core is easily saturated at a large current, simulations are performed to analyze the influence of air gap distribution on magnetic flux intensity in the transformer. An electromagnetic current transformer core structure is designed, which can still effectively work at the 15 kA short-circuit current peak. The 3D transient electromagnetic simulations show that when the short-current rising rate is 20 A/µs and the number of turns in the secondary winding is 30, the output voltage from the secondary winding is not less than 14 V. Finally, an engineering prototype of hybrid current-limiting fuse with a passive electromagnetic current transformer as its trigger device was made, and a short-circuit current detection test was carried out. The experimental results basically agreed with simulations, indicating the accuracy and validity of the design of iron core.