Motor noise is the combination of different frequency and intensity of sound, this annoying noise hazards are well known to mankind. Often associated with oscillation and noise attack, excessive oscillation will also damage other equipment. Vibration noise level reflects the product planning, production level, is an important index to measure the quality of products. Now people are already pervaded realize the importance of down noise. Motor planning, production and operation personnel needs more common sense about the motor noise. Demand, for example, figure out how motor noise attack, and what factors related, expectations in the planning stage to estimate noise of motor practice runs on attack, together to know drop method of noise and so on. Electromagnetic noise is caused by alternating electromagnetic field changes and some mechanical parts or space volume of oscillation. For motor, because of unstable power supply can also stimulate the stator vibration and noise. The primary characteristics of electromagnetic noise and alternating electromagnetic field characteristics, forced oscillation intrusive elements such as the shape of parts and space. The high frequency electromagnetic noise, also known as the electromagnetic noise. Reason analysis of motor electromagnetic noise attack run oil-gas gap exists in the fundamental wave magnetic field and a series of harmonic magnetic field, the magnetic field effect attack each other tangential force, tangential electromagnetic torque, to attack will also attack along with the time and spatial changes of the radial force. In general, motor air gap exists in various times, various frequency rotation of radial electromagnetic wave. Each radial force wave effect on the set, the rotor core respectively, the stator core and the frame and the rotor radial deformation of periodic changes over time, the onset of oscillation, the oscillation frequency is the frequency of the wave effect. Stiffness is very big, because the rotor core had a seizure of oscillation is very small, so usually only consider the oscillation of the stator core and the frame. Electromagnetic noise first because the stator oscillation caused by the surrounding air pulse of airborne noise. Radial force wave of the lower order number, core winding deformation of the farther the distance between the adjacent two fulcrum, core relatively poor stiffness, radial deformation. Deformation around the stator core and the inverse proportion, four times the number of wave force is proportional to the force amplitude value, so the low amplitude of the larger number of radial force wave is the first source of electromagnetic noise cause, in addition, should pay special attention to is the core and base have certain inherent oscillation frequency, when the radial force wave frequency and the natural frequency near together, even will attack resonance, the core of oscillation and radiated noise will greatly add. Because of fundamental wave amplitude of magnetic field is bigger, and if there is no fundamental wave magnetic field, the motor can't work, so the noise by the frequency doubling of its attacks are not prevent. But because of its high wave number (In addition to the 2 pole motor), the frequency is low, the noise radiation efficiency is lower, therefore, in addition to the larger of the 2 pole motor power, frequency multiplication noise is generally small. Motor primary noise source analysis of the primary noise source has electromagnetic noise, mechanical noise and ventilation noise. Low electromagnetic noise in the motor air gap magnetic field effect attack each other with the time and spatial changes of the radial force, always keep the stator core and the frame with periodic deformation, namely, the stator attack oscillation; The oscillation of the stator electromagnetic noise first because the surrounding air pulse caused by airborne noise. Low machinery noise rotor imbalance caused by centrifugal force attack by the mechanical vibration and noise, bearing vibration noise, brush and collector ring or commutator noise, bearing vibration excitation of sliding contacts, the end cover of the axial vibration noise, etc. Low noise fan ventilation or other ventilation components as well as the rotor spinning forming air vortex noise, cooling air fan rotation make periodic pulsation obstacles or gas lighting strike and the onset of single frequency noise, the wind thin-wall parts in resonance or the wind road planning of unreasonable attack & other; The flute & throughout; 。 Motor electromagnetic noise to distinguish motor electromagnetic noise tests with the magnetic field strength, load current range and speed high and use this feature, can adopt the following measures. When the power law. Because much more slowly than the electromagnetic transition process, mechanical inertia and power outages, no electromagnetic factor influence, the motor speed is almost the same. If the motor noise and Russia but disappeared or significantly decreased, the noise of the attack can be concluded that the electromagnetic reasons. Low voltage method. Because of the asynchronous motor speed with the voltage change is not big, when the voltage changes, mechanical noise and ventilation noise basically remain unchanged, but the electromagnetic noise voltage changes a lot. Low drag method. With a low noise motor drive noisy subjects motor, at this time if the noise drops or disappear, then the dragged motor noise is electromagnetic noise. Electromagnetic computing electromagnetic noise is one of the primary noise source of the motor, the multi-polar several motor or ventilation with low noise, electromagnetic noise becomes more prominent, usually it increases with the motor power and add, and it is the increase of load noise source. The noise is closely related to the electromagnetic planning parameters of the motor, such as planning, electromagnetic noise will be quite significant, may be the most primary noise source than that of other noise. Thus, discussion motor electromagnetic noise attack causes, planning parameters associated with electromagnetic noise and electromagnetic noise calculation method, in the planning stage to estimate and control motor noise is important.
