Nigerian Journal of Engineering Science and Technology Research

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Several methods have been proposed in literature for the estimation of induction motor efficiency under sinusoidal supply condition. However, only a few of those methods can be considered suitable for motors operating under distorted or non-sinusoidal supply condition. In this paper a new method is proposed for induction motor efficiency estimation under non-sinusoidal supply conditions - to take into account the presence of harmonics in the power supply. By using a modified equivalent circuit approach, the method considers the variations of the core loss resistance due to time harmonics. Also, the changes in the rotor bar resistance and the leakage inductance due to skin effects at higher frequencies is considered in the harmonic equivalent circuit. Two induction motors of different design classifications are tested to validate the proposed method under different levels of voltage unbalance and harmonics conditions. These two motors are a 37kW standard efficiency and a 7.5kW premium efficiency induction motors. Finally, the efficiency estimation via the proposed method is compared to the IEC60034-2-3 standard in the case of a balanced non-sinusoidal supply condition. This allows not only the efficiency comparison but also the loss segregation analysis on the various components of the motor losses. In the case of an unbalanced supply, the efficiency results are compared to measured values obtained via the direct input-output method. The results obtained indicate that the maximum absolute efficiency errors at 9.96% 〖THD〗_v for the 7.5kW and 37kW test motors were found to be 0.234% and 0.248% respectively. These values confirm the accuracy of the proposed method.

Authors : Aminu, M.

Category : Open Access     Volume (Issue) : 8(1)     Date Uploaded : 6th August 2022

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