Current transformer and method of manufacturing the same

A current transformer comprising:

• a resin-made bobbin with a through hollow section, the bobbin having a primary coil and a wire-wound secondary coil;
• and
• a core consisting of E-type cores and I-type cores provided in the hollow section of the bobbin, wherein each of the E-type cores is formed of an electromagnetic steel sheet and has three legs extending substantially parallel to each other and a connecting part connected at each end of the legs, and each of the I-type cores is formed of an electromagnetic steel sheet and has the same length as the connecting portion, wherein the E-type cores are stacked with its central leg alternately in opposite directions, and the I-type cores are placed between the connecting parts of the stacked E-type cores,
• the core comprising a plurality of core components,
• wherein each of the core components has an E-type core formed by press-punching an electromagnetic steel sheet and has three legs extending substantially parallel to each other and a connecting part at each proximal end of the legs, and an I-type core formed by press-punching an electromagnetic steel sheet and has the same length as the connecting part of the E-type core, the I-type core being placed on and bonded to the connecting part of the E-type core to form a one-piece structure of the E-type core and the I-type core,
• wherein each of the core components is inserted into the hollow section of the bobbin from a first direction and a second direction opposite to the first direction alternately while interchanging the top and bottom of the core component to form a stack structure of the core components,
• wherein the E-type core and the I-type core with end faces prepared by the press-punching process have a rounded, slope shaped, sheared surface on their corners, a sheared surface with striations formed in the thickness direction, a fractured surface with unevenness as if the steel sheet was plucked, and a jagged burrs protruding from the end face in the punching direction,
• the E-type core and the I-type core of each core component are arranged such that the sheared surface and the fractured surface are opposed to each other.