Nine-phase armature windings design, test, and harmonic analysis

A nine-phase armature winding was developed for a large generator. Alternative methods for interconnecting the pole-phase groups were examined. An alternate-pole connection scheme was adopted and a prototype induction motor was constructed to confirm the winding scheme. Since only a three-phase power source was available for testing, the induction motor was tested by using three, three-phase winding sections, one at a time. Air-gap harmonic fields produced some unusual results. These test results and harmonic analyses to explain them are presented herein. The tests confirmed the nine-phase winding scheme that was adopted. The harmonic analyses revealed that the complete nine-phase winding exhibited a very low harmonic content, a distinct advantage of a nine-phase winding for future applications.