A low harmonic, high spread factor induction motor

Theoretically, a conventional 60° phase spread winding can be subdivided into two components, one of which is connected in star and the other in delta. The two components may occupy different electrical spacing. According to the new principle, a 3-phase induction motor is designed with the two winding components being connected in series to 3-phase power supply. Analysis has shown that this new type of machine has a high winding coefficient and low harmonic content. The winding can be arranged in technological short-pitch. The ratio of the number of effective turns and cross-sectional area between star and delta winding components should be theoretically in 1:√3 and √3:1 respectively, but slight difference is allowed in practice. The analysis of the MMF. harmonics proves that the harmonic content is remarkably reduced in the new winding. The tests of the prototype machines showed that the new type of the motors has an improved performance. Also, the test results showed that there is no overheating behaviour for new winding motors to operate at normal load.