Understanding Motors Having Permanent Magnet

By Author: Permanent Magnet, Magnetic Filter Rod
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Using magnets imbedded into or attached to the motors rotor’s surface, a permanent magnet (PM) motor is an ac motor. Behind the physics, concepts, terminology, and theory behind PM motors, this article provides an elementary understanding.

Using a variable frequency drive (VFD), controlling the speed of ac motors and Magnetic Filter Rod is accomplished in most cases. They also can achieve position feedback sensors or precise speed control using speed as a reference to the VFD.

Induction machines

An ac motor also is commonly referred to as an ac induction machine (IM). By the stator winding, a rotating field is generated. In the rotor bars, the rotating field induces a current. Between the magnetic field and the rotor, the current generation requires a speed difference.

The driving force is produced by the interaction between the current and the field. Therefore operated by adjustable speed drives, ac induction machines are the predominant motor.

PM motors

Using ...
... magnets attached to or imbedded into the surface of the motor’s rotor, A PM motor is an ac motor. Instead of requiring the stator field to generate one by linking to the rotor, the magnets are used to generate a constant motor flux as is the case with an induction motor. Characteristics of both motors are incorporated in a fourth motor known as a line-start PM (LSPM) motor.

Permanent magnet demagnetization

Permanent magnet does have limited capabilities and are hardly permanent. To demagnetize them, certain forces can be exerted onto these materials. In other words, removing the magnetic properties of the permanent magnet material is possible.

If the material is impacted by a large electrical disturbance, allowed to reach significant temperatures, or is significantly strained, a permanent magnetic substance can become demagnetized.
First by physical means, straining a permanent magnet is done typically. If not weakened, a magnetic material can become demagnetized, if it was to experience violent falls or impacts. Inherent magnetic property is there in a ferromagnetic material. However emitting in any multitude of directions, these magnetic properties are reliable.

By applying a strong magnetic field to the material to align its magnetic dipoles, one way ferromagnetic materials are magnetized. Weakening the strength of the intended magnetic field, a violent impact can remove the atomic alignment of the material’s magnetic domains.

Secondly, a permanent magnet is affected by temperatures. In a permanent magnet, Temperatures force the magnetic particles to become agitated. To withstand some amount of thermal agitation, the magnetic dipoles have the ability. To define magnetic material strength retention capability, terms such as retentivity and coercivity are used.

Finally, to demagnetize, large electrical disturbances can cause a permanent magnet. If a large current is passed through the material or interacting with a large magnetic field, these electrical disturbances can be from the material. To align a material’s magnetic dipoles, much in the same way a strong magnetic field or current can be used another strong current applied or magnetic field to the field produced by the permanent magnet can lead to demagnetization.