The S20 series oil immersed three-dimensional coiled iron core transformer iron core is assembled from three identical frames. When cutting silicon steel longitudinally, it can achieve nearly 100% utilization through nesting cutting, with less leftover material at the edges and corners. Silicon steel sheets are tightly wound and seamless, with high iron core filling coefficient and low magnetic resistance. Continuous winding can ensure that the magnetic conductivity direction of silicon steel is consistent with the actual magnetic flux direction. The length of the three-phase magnetic circuit of the three-dimensional coil iron core is consistent, which can achieve three-phase magnetic circuit balance, significantly reduce no-load loss and no-load current, and reduce noise by more than 10dB. The product is widely used.