Combined star-delta windings in small induction machines for reducing no-load and additional losses

This paper presents a combined star-delta winding design for reduced core losses in squirrel cage induction machines. The study focusses on small machines with single layer integer slot distributed windings with relatively high stator resistance. Theoretical considerations show that machines with combined star-delta windings can be operated bidirectionally by swapping two phases of the supply voltage. Combined windings typically increase the fundamental winding factor and decrease the harmonic content in the air-gap field. Therefore, new formula are derived for the harmonic leakage coefficient and the increase in the fundamental winding factor due to a combined winding. A 4 kW motor is investigated analytically using the well-known perphase equivalent circuit. Measurements are presented to prove that the combined winding reduces core losses, magnetizing current and additional losses effectively. Finally, comments are given on the generalization of the results.