This invention relates to a transformer whose valtage tap can be changed from three-phase system to two-phase system and the equilibrium transformer has a third voltage tap. The subside voltage vector diagram is similar to "A", and there is "star" type connection or "triangle" type connection in the original sides. The third voltage is introduced out from the top points of triangle contained in "A" shape, and it can be used for compensations for no work and other loads. The vector's phase position and voltage volume are decided by the coil numbers and its connection. The needed resistance is determined by each other's position between coils or between coil and iron core. |