The wound core is made of cold rolled high carbon silicon steel sheet. It is wound into a closed frame-shaped structure by annealing treatment, Wound core is with high filling factor. There is no air gap in the magnetic circuit. Both HV and LV windings are continuously wound on the core limb with good concentricity and performance of tightness. With characteristics of low loss and low noise, it is the new generation of high-tech, high-performance, and energy-saving products, widely used in power supply and distribution system.