High Frequent Noise from Variable Speed Drive Electric Motors
Tuesday 2 june, 2015, 09:40 - 10:00
0.6 Madrid (49)
Large electric motors are normally noisier when connected to a frequency converter, also called a variable speed drive. The extra noise is caused by over harmonic frequencies generated by the frequency converter panel. The purpose of the frequency converter panel is to generate an electric sinus signal with a different frequency than the incoming frequency from the power grid. The characteristic sound frequency emitted by the motor is dependent of the type and set up of the frequency converter panel. Thyristor equipped panels generate a frequency which is dependent of the number of thyristors included in the panel. The disturbance/fluctuations on the sinus curve is being transmitted by the power cables to the electric motor and transmitted as noise from the motor casing. Narrowband analysis show that the noise emitted at the characteristic frequency is up to 40 dB above the adjacent frequency bands. The noise can be reduced by locating filters between the frequency converter panel and the motor. Another mitigating action is to use a different type of frequency converter panel which generate less fluctuations on the generated sinus curve. The potential overall noise reduction is about 10 dB.
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