Attenuation of electromagnetic acoustic noise from a variable speed induction motor by using dynamic vibration absorber

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Date
2016-03-01
Authors
Vigren V.Radha
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Tonal electromagnetic acoustic noise radiated from variable speed induction motor can be annoying to human operator. Occurring at high frequency, it often occurs at multiples of the inverter switching frequency. Solutions for the noise attenuation have been generally by means of electromechanical design and pulse width modulation (PWM) strategy to remove harmonics leading to noise generation. Dynamic vibration absorber (DVA) as an alternative solution was implemented in this research. Spectral test revealed that the input electromagnetic excitation has direct influence on the radiated electromagnetic acoustic noise from the induction motor. The multiples of 3 kHz harmonics in PWM spectrum was also present in the surface vibration and sound pressure spectrum. From experimental modal analysis and spectral test, it was found that the 6 kHz acoustic noise was due to forced vibration for speed of 1250 rpm and below. While at above 1250 rpm, the 3 kHz noise was due to resonance. A 20mm M6 bolt was used as DVA and attached to a point on the motor housing for targeted noise attenuation at 6 kHz. The DVA was able to absorb the surface vibration in the range of 20 to 86% and maximum sound pressure level reduction of 12 dB (A) was achieved. It was also effective at other locations on motor as well as at different operating speed. The DVA was thus proven to be a feasible method for electromagnetic noise attenuation in induction motor.
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