Space harmonic fields caused by rotor harmonic currents of induction motors (IMs) under no-load condition may significantly affect motor performance

especially for inverter-fed condition. As to development of high-efficiency and low vibration IMs

it is also a challenge to accurately reveal the influence of harmonic fields on loss and vibration. This study firstly clarifies the source of rotor harmonic fields

and analyzes the influence of those harmonic fields on stray losses qualitatively. With a 5.5 kW induction motor with and without rotor bars

as well as non-skewed and skewed rotors

the stator harmonic currents and the harmonic flux density distribution in typical positions of core under no-load condition are comparatively analyzed

respectively. It is revealed that the rotor harmonic fields can increase harmonic iron loss and harmonic copper loss at the stator side. However

due to the harmonic damping effect

the stray iron loss at the rotor side is effectively reduced. The results show that

compared to the IM without rotor bars

the stator stray iron loss increases by 9.55% and 5.45%

and the harmonic copper loss increases by 16.97% and 1% under the conditions of non-skewed and skewed rotors

respectively. But the rotor stray iron loss decreases by 29.53% and 4.86% under the conditions of non-skewed and skewed rotors

respectively. The generality of this effect is further verified by analyzing no-load stray losses of three motors with the rated power of 75 kW

200 kW and 1 600 kW. Finally

four prototypes identical to the simulation cases are manufactured and the theoretical and simulated results are validated by the experiments.