High Frequent Noise from Variable Speed Drive Electric Motors
Regular paper
Multiconsult
Tuesday 2 june, 2015, 09:40 - 10:00
0.6 Madrid (49)
Abstract:
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.