Adapt the interleaved winding or inner screen continuous structure to improve the distribution of the impulse voltage wave, which ensure the HV winding insulation strength. Medium and low voltage coils are made of high strength semi-hard oxygen free copper conductors with the continuous type or spiral type structure. During the winding process, we use the coil straining devices to make the turns tension along a circumference direction and no crosswise difference. We adapt strengthened cooling insulation structure for the inner side of HV and LV coils to make the coils temperature rise. With the addition of rational structure design, turns distribution balance and low flux leakage, the coils have high anti-short circuit and overload ability.