The utility model discloses an open -type zero sequence current transformer belongs to mutual -inductor equipment field. It includes the iron core, the winding has the secondary line on the iron core,is provided with two semicircular epoxy shells on the iron core periphery wall, through fixing bolt fixed connection between the epoxy shell, one of them epoxy shell top is provided with two secondary bolts, and two secondary bolt outsides are covered with the secondary separate terminal enclosure, and another epoxy shell top is passed through base fastening bolt and is installed base fixed connection, the one end and the secondary bolted connection of secondary line, the other end is connected with the secondary connection piece, the secondary connection piece sets up between the iron core.The utility model discloses an open -type zero sequence current transformer, dielectric strength is high, and mechanical properties is good, is applicable to heavy current, big specification cable, and the protection multiple is higher, and the relay protection that the capacity is bigger uses.