Sources of noise and vibration in electrical machines
Noise sources in electrical machines are generally classified in three sources:
- electromagnetic noise of electrical machines (e.g. magnet/slot interactions due to Maxwell forces)
- aerodynamic noise of electrical machines (e.g. fans)
- mechanical noise of electrical machines (e.g. bearings)
Aerodynamic noise is generally due to shaft-mounted fans, so it increases with speed. Its frequency depends on the number of blades and it is characterized both harmonic tones at blade passing frequencies, and broad band noise due to turbulence.
Mechanical noise due to bearings increases with speed but its frequency is generally too low to create significant noise issues.
Electromagnetic noise is characterized by strong tonalities, its frequency content depends on the control law applied at variable speed, and more especially on the Pulse Width Modulation strategy.
Audio example
The run-up of an electric motor including electromagnetic, aerodynamic and mechanical noise sources can be listened here:
- Total noise of a traction electric motor during run-up (aerodynamic, mechanical and electromagnetic sources)
Each source has been isolated based on its frequency characteristics to obtain separate sound files for each noise source.
The contribution of mechanical noise alone can be listened here:
- Mechanical noise of a traction electric motor during run-up
The contribution of aerodynamic noise alone can be listened here:
- Aerodynamic noise of a traction electric motor during run-up
The contribution of electromagnetically-excited noise alone can be listened here:
- Eletromagnetically-excited noise of a traction electric motor during run-up
One can notice that the sound is very close from the synthesized sound of electrical machines calculated with MANATEE software.