A current transformer comprising: a first transformer assembly, two ends of the first transformer assembly being provided with a first assembly end and a second assembly end, the first transformer assembly comprising a first group of stacked iron core components, the first group of iron core components being provided with a first interface defined at the first assembly end and a second interface defined at the second assembly end; a second transformer assembly, two ends of the second transformer assembly being provided with a third assembly end and a fourth assembly end, the second transformer assembly comprising a second group of stacked iron core components, the second group of iron core components being provided with a third interface defined at the third assembly end and a fourth interface defined at the fourth assembly end; and a plurality of coils, the plurality of coils comprising a first coil, second coil, third coil, and fourth coil, wherein at least one of the first interface and the second interface is detachably connected with at least one of the third interface and the fourth interface, so as to detachably connect the first transformer assembly and the second transformer assembly; the first transformer assembly and the second transformer assembly are configured such that when connected with each other, the first group of iron core components and the second group of iron core components are combined to form a plurality of closed ring-shaped iron cores, and at least two closed ring-shaped iron cores (221, 222) of the plurality of closed ring-shaped iron cores are respectively wound with one of the first coil and the second coil; an enclosed area is defined between the first transformer assembly and the second transformer assembly such that when a cable under test passes through the enclosed area, an induced current related to current in the cable under test is generated in at least one coil of the plurality of coils; the fourth coil is configured to generate induced current related to the current in the cable under test when the cable under test passes through the enclosed area, characterized in that the first and second coils (W1, W2) are arranged to determine a DC component of the induced current, and the third coil is arranged to detemine an AC component of the induced current. a first transformer assembly, two ends of the first transformer assembly being provided with a first assembly end and a second assembly end, the first transformer assembly comprising a first group of stacked iron core components, the first group of iron core components being provided with a first interface defined at the first assembly end and a second interface defined at the second assembly end; a second transformer assembly, two ends of the second transformer assembly being provided with a third assembly end and a fourth assembly end, the second transformer assembly comprising a second group of stacked iron core components, the second group of iron core components being provided with a third interface defined at the third assembly end and a fourth interface defined at the fourth assembly end; and a plurality of coils, the plurality of coils comprising a first coil, second coil, third coil, and fourth coil, wherein at least one of the first interface and the second interface is detachably connected with at least one of the third interface and the fourth interface, so as to detachably connect the first transformer assembly and the second transformer assembly; the first transformer assembly and the second transformer assembly are configured such that when connected with each other, the first group of iron core components and the second group of iron core components are combined to form a plurality of closed ring-shaped iron cores, and at least two closed ring-shaped iron cores (221, 222) of the plurality of closed ring-shaped iron cores are respectively wound with one of the first coil and the second coil; an enclosed area is defined between the first transformer assembly and the second transformer assembly such that when a cable under test passes through the enclosed area, an induced current related to current in the cable under test is generated in at least one coil of the plurality of coils; the fourth coil is configured to generate induced current related to the current in the cable under test when the cable under test passes through the enclosed area, characterized in that the first and second coils (W1, W2) are arranged to determine a DC component of the induced current, and the third coil is arranged to detemine an AC component of the induced current.