Part-winding starting improvement of three-phase squirrel-cage induction motor

Partial-parallel-path-winding starting of three-phase induction motors is used in order to reduce the starting currents in hard-load condition, as it is the case of special compressors application. In the paper, two possibilities of winding arrangement are analysed from the point of view of air gap field, taking into account the upper space harmonics of the rotating mmf. Using the Fourier analysis of the air gap field it is shown the best way to choose the parallel path connection, the pitch of the coils and the number of turns in order to minimise the noise during starting and to obtain satisfactory starting performance (torque and current). Examples are given for four-pole three-phase induction motors with odd number of slots per pole per phase in order to compare different winding arrangements.