Harmonic Analysis for Induction Motors

Two types of harmonics are investigated for induction motors: space harmonics and time harmonics. Space harmonics are generated due to the different phase windings interaction when the power supply is sinusoidal and they can be reduced by applying a proper machine design. As an example, the electromagnetic field and corresponding harmonics of an electrical machine are calculated using the finite element method, the harmonic winding factors show how the space harmonics can be reduced significantly by good winding design. Because of the wide application of variable frequency drives, time harmonics have become a main concern related to motor performance in field operations. The harmonic equivalent circuits are presented in this paper for both space and time harmonics and they are powerful tools to calculate the motor parameters such as harmonic currents and torques. The formulas to calculate the harmonic slips and torques are derived, and the torque characteristics for both types of harmonics are compared