Abstract: Circular power CT is a very important passive self supply module for online monitoring products of high-voltage transmission lines. It is used to solve the problems of semi circular CT winding and automatic counting of turns in small-scale trial production or mass production processes, and to improve production efficiency. By measuring and analyzing the winding tension of enameled wire, calculating the motor torque load capacity, 3D modeling, mechanism motion simulation, motor selection, controller selection, electronic and electrical component selection, and structural evaluation of mechanical components, the design concept of the winding device is achieved, and the application of semi circular CT winding for enameled wire with a diameter of 1.0 mm and below is verified.