The open-closed current transformer is improved on the basis of the traditional transformer. Made of free opening and closing, it can be quickly installed and disassembled in the state of no power failure and no wire disassembly, and the operation is sample. This series of products has a wide measuring range, rated primary current range 5~630A, rated secondary current range 0~5A, current ratio range can reach 500:1~ 10 000:1, orderly production process, to ensure its accuracy level, reliability and other technical requirements. This products complies with GB/T20840.1.2 Standard.