Detection of the space harmonics of the shaded pole induction motor
Abstract
In many cases, shaded pole induction motors have variable air gaps, and because of this, their air-gap flux density waveforms are too far from a sinusoidal distribution. Utilizing of variable air-gap in shaded pole motors contributes to the starting torque by inducing reluctance torque
component. However, variable air-gap introduces additional harmonic components in the airgap flux density waveforms. In this study, detection of the space harmonics of the shaded pole induction motor has been realized. To be able to detect the space harmonics, the rotor of the motor has been produced in a way that aluminum has not been cast, and the short circuit rings of the rotor has have not been inserted. A search-coil whose number of turns is known has been wound to the rotor, rated voltage has been applied to the stator, and the position of the rotor has been varied with a step electrical angle of 3.6o with the help of a step motor. The mutual inductance between the stator and rotor has been determined by reading the voltage induced across the search-coil. The
attained mutual inductance waveform has been subjected to Discrete Fourier analysis. From the analyses, it has been observed that especially the 3rd, 5th, and 7th harmonics, especially, are very significant. Other harmonics up to 13th are above 1% of the fundamental component, and the 15th and subsequent harmonics decreases below 0.8% of the fundamental component of the air-gap flux density waveform. Therefore, for a reasonably accurate performance, an analysis of this these machines, at least 3rd, 5th, and 7th harmonics, should be considered.
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