The clock-number notation method is the basis of three-phase transformer connection group judgment.This paper presents a disk discrimination method,which combines the advantages of the clock-number notation method,gravity center coincidence method and the engineering test method.The combination of 144 kinds of connection on a disk has the characteristics of accuracy,intuitive,simple and practical.The examples show that it can be widely used in the teaching of professional basic courses,such as Electrical Machinery、Motor and Drag Foundation and...