Main noise source analysis of the motor
The main noise sources of the motor are electromagnetic noise, mechanical noise and ventilation noise.
●Electromagnetic noise
The magnetic field interaction in the air gap of the motor produces radial force that changes with time and space, so that the stator core and the base are periodically deformed with time, that is, the stator vibrates; the electromagnetic noise is mainly caused by the vibration of the stator causing the surrounding air to pulsate. Load noise.
●Mechanical noise
The mechanical imbalance of the rotor causes mechanical vibration and noise generated by centrifugal force, bearing vibration noise, sliding contact noise of the brush and the collector ring or the commutator, and axial vibration and noise of the end cover excited by the bearing vibration.
● Ventilation noise
Fan or other ventilating elements and air eddy currents caused by the rotation of the rotor, single-frequency noise generated by the rotation of the fan to periodically pulsate the cooling air or gas impinging on obstacles, or the unreasonable design of the thin-walled parts in the wind path or the wind path design Flute."
Motor electromagnetic noise identification
The electromagnetic noise of the motor varies with the strength of the magnetic field, the magnitude of the load current and the speed of the motor. With this feature, the following methods can be used for identification.
● Sudden power-off method. Since the mechanical inertia is much slower than the electromagnetic transition process, the power is suddenly turned off and there is no electromagnetic influence. At this time, the motor speed is almost constant. If the motor noise suddenly disappears or drops significantly at this time, it can be concluded that the noise is caused by electromagnetic causes.
● Change the voltage method. Since the speed of the asynchronous motor does not change much with the voltage, when the voltage is changed, the mechanical noise and the ventilation noise are basically unchanged, but the electromagnetic noise varies greatly with the voltage.
● The method of dragging. A noisy motor is used to drag a noisy motor under test. If the noise is reduced or disappears, the motor noise being dragged is electromagnetic noise.
Electromagnetic noise calculation
Electromagnetic noise is one of the main noise sources of motors. In multi-pole motors or motors with low ventilation noise, electromagnetic noise is more prominent. Generally, it increases with the increase of motor power, and it is increased noise during load. Big roots. This noise is closely related to the electromagnetic design parameters of the motor. If the design is improper, the electromagnetic noise will be very obvious, and it may become the most important noise source exceeding other noises. Therefore, studying the cause of electromagnetic noise of motor, the relationship between motor design parameters and electromagnetic noise and the calculation method of electromagnetic noise are of great significance for predicting and controlling motor noise in the design stage.
