Induction motors are the most typical motors in use right now. Motor noise can be a problem for most motor suppliers. So what leads to motor sounds and what can be carried out to minimize the sounds? In this write-up we will go over in which motor sounds will come from and how it can be minimized.
The three standard types of electric motor noise are:
1. Magnetic Sound
two. Bearing Sounds
3. Unbalance Noise
MAGNETIC Sound:
The major supply for magnetic noise in induction motors arrives from force waves created by the rotating magnetic area. Given that this area is the vehicle by which electricity is transmitted from the stator to the rotor, elimination of this sounds is not attainable. However, magnetic sounds can be minimized by making use of many methods:
one. Making use of the proper stator and rotor slot mix
2. Planning the stator and rotor lamination geometry
3. Implementing the correct coil pitch
4. Formulating the appropriate rotor skew
The suitable choice of stator and rotor slots is one of the most critical aspects of a peaceful motor design. This selection also influences production costs. To maintain producing charges minimal, the variety of stator slots must be the variety of poles occasions the number of phases in a presented frame size. This amount of stator slots should be this sort of that a well balanced winding can be accommodated. There are barely any slot combos that are excellent however, above the a long time there have been some combos that have established to be profitable. The subsequent basic rules ought to be utilised as a tutorial when creating the lamaintions:
a. The number of rotor slots ought to not equal the quantity of stator slots. Appropriate performance has been attained when the variety of rotor slots differs by the number of stator slots by fifteen to thirty%. b. To keep away from dead factors or cogging, the distinction between stator and rotor slots must not equivalent +/- variety of phases occasions number of poles c. To decrease noise and vibration the difference in between the amount of stator slots and rotor slots should not equal +/-1, +/-two, +/- (quantity of poles+/-one) and/or +/- (variety of poles +/-2). For case in point: if you have a 6 pole motor and the stator lamination has 18 slots then the rotor laminations should not have the adhering to number of slots: 17, 19, 16, 20, thirteen, 23, 14, or 26.
When creating the stator and rotor lamination geometry, several parameters should be reviewed. A shut rotor slot will result in significantly less permenace variation, even so, thickness of the bridge must be reviewed to make sure the lamination does not saturate. The width of the stator slot opening really should be stored to a least however you still want it huge sufficient to insert the coils. The duration of the air gap also influences permeance variation such that the greater the gap the much less the variation. But preserve in brain, the air gap also is dependent on the other design and style standards such as power element and performance. The motor design engineer needs to get into account all needs when developing laminations.
Using the suitable stator coil pitch is additionally important. The stator coil pitch ratio really should be chosen to give little pitch variables for decrease purchase of air gap harmonics. The motor designer will need to have to preserve this in thoughts when developing the winding. Skewing of either rotor or stator slots is another way to minimize motor sounds and provide easy acceleration. The diploma of skew also has an effect on induction motor performance, consequently the skew is minimal to overall performance parameters this sort of as breakdown torque, commencing torque and starting up currents.
BEARING Sound
Bearing sounds can be motivated by many variables these kinds of as preload, shaft to bearing fits/tolerances, and bearing to bore matches/tolerances. The selection to which bearing to use really should constantly depend on the app of the motor. It is extremely recommended to involve bearing manufactures when picking the bearing.
Suitable preloading is required to make sure the bearings run easy. As well significantly preloading will injury the bearings. Identical philosophy goes with the bearing matches to the motor shaft and housing and stop bell bores. Bearing manufactures have advised fits/tolerances to apply in the course of the mechanical layout of the motor.
UNBALANCE Sound
Unbalance sounds is developed by an unequal weight distribution of the rotor assembly close to the motor axis of rotation. It has been found that vacuum impregnation and/or encapsulation of motor stator windings has also helped in coil vibration and sounds. There are a lot of approaches to lessen motor sound. All motor parameters have to be taken into account when designing the device.