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This study deals with the influence of voltage subharmonics and interharmonics on an induction cage machine. The windings current subharmonics and interharmonics as well as the magnetising current are studied. The effect of voltage subharmonics and interharmonics on windings temperature rise is analysed. The results of measurements and calculations are compared for various machine models. The appropriate investigations are performed for two low-power, totally enclosed induction motors of different properties: a machine with a comparatively strongly saturated magnetic circuit, and one with a comparatively weakly saturated magnetic circuit.

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In some power networks, components of frequency less than the frequency of the fundamental voltage harmonic called subharmonics or subsynchronous interharmonics occur. In this paper, the effect of voltage subharmonics on currents, power losses, speed fluctuations and electromagnetic torque is examined. The results of numerical computations using the finite element method for an induction cage motor of rated power of 5.6 MW and four motors of rated power of 200 kW with different numbers of poles are presented. An extraordinary harmful effect on high-power induction motors is demonstrated. Among other effects, voltage subharmonics cause significant torque pulsations whose frequencies may correspond to the elastic-mode natural frequency. Possible resonance can result in excessive torsional vibration and the destruction of a power train.