This series of products break through the traditional flat structure and adopt three-phase symmetric three-dimensional structure. The cross section of core column and iron yoke is approximately a round shape with high section filling coefficient. There is no gap in magnetic circuit, iron core magnetic circuit of three phase of the product are completely symmetrical and three phase are balanced; magnetic circuit are equal and the shortest. The magnetic circuit and no-load loss are significantly reduced. It’s one high-efficient and energy-saving type transformer used traditional materials with lower running noise and much compacted structure. The iron core is composed of three identical single frames forming one equilateral triangle which are of good stability, high mechanical strength and consistent three-phase stress. The winding of the product is circular. The connection turns numbers of high-voltage winding is optimized according to ampere-turn balance requirement. And the product has strong short-circuit resistance.