Abstract
Environmental concerns have increased demand for induction motors with low noise characteristics. Electromagnetic noise has been a particularly concern. Relation of electromagnetic noise and natural frequencies has been studied for more than twenty years. However, a new phenomenon has arisen, in which motor noise changes with increase in motor temperature. In this study, the relation-ship between electromagnetic noise and temperature was analyzed quantitatively. It was found the relation of electromagnetic noise and temperature as follows. In temperature 20-70°C, noise level does not varies, but in temperature 70-140°C noise level decreases drastically by 6 dB (A) at first and then increases by 3 dB (A). Natural frequencies of 273 Hz and 350 Hz appear at 20°C, and two natural frequencies unite at 70-140°C in the experiments. A two-degrees of freedom system with core and coil end considering temperature effects was used for calculation of the natural frequency. These calculated values agreed with experimental results. The relation between variation of the natural frequency and temperature in electromagnetic noise was analyzed and the cause of noise variation with temperature was clarified.
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