Abstract: There are various connection methods for threephase transformer. It is stipulated internationally with clockdenoted method that the linking groups of threephase transformer are symbolized by the relationship between the first side linepotential and the second one of the threephase transformer. But this linepotential can not reflect the real linking of the transformer windings direetly. This paper presents a new method to determine the linking groups of threephase transformer based on the voltage phase relationship. The linking groups of transformer are confirmed by rotating the voltage vectors of second side according to the phase between the first and second side phasevoltage. The analytic course is simple and directly perceivable, the concept of left/right triangle wiring mode of three phase windings is proposed. It is also a new method of power electronics subject education.

Key words: vector analysis, threephase transformer, left triangle, right triangle , voltage vector