What is an Induction Motor?
An induction motor is a motor that provides power. It owes its name to the way it operates. Alternating current (AC) voltages are induced by the magnetic and rotating field of the stator in the rotor circuit. An induction motor is constructed with elements of copper, steel, and aluminum. While this makes them more expensive than universal motors, it also increases their quality and durability.
The construction of an induction motor is almost identical to the construction of a three-phase synchronous motor. It consists of a rotor that is manufactured from a laminate cylinder with a slotted surface. The windings in these slots can be one of three types: a squirrel-cage winding, a slip ring rotor, or a solid core rotor.
A squirrel-cage winding is made of copper bars that span the length of the rotor. They are connected at each end through a ring. The rotor bars are skewed and not straight in order to reduce noise.
Slip-ring rotors do not contain the bars found in squirrel-cage rotors. Instead, they contain windings that are connected to slip rings. If the slip rings are shortened, it causes the rotor to behave much in the same way as squirrel-cage rotors. Solid-core rotors induce the current needed to rotate and are made from solid steel.
Inductor motors are slower than universal motors and have a lower start-up torque. The speed of the motor is controlled by the number of windings in their stator and by the supply of voltage. In order to induce voltage, the speeds of the rotor and the rotating magnetic field in the stator must differ; otherwise, the magnetic field will not move relative to the rotor and no voltage or current will be induced.
Their slower speed contributes to their longevity as well as their consistent and reliable use. They are not prone to out as universal motors are. Induction motors also are usually very quiet.
Almost all table saws are fitted with an induction motor. The appropriate size motor depends on the saw. While smaller saws would use a motor between 1 and 5 horsepower, larger saws need fan-cooled induction motors. This is designed for continuous use and they are designed in a way that they are sealed against dust.
An induction motor is able to drive at a constant speed. Their three-phase construction produces a motor that generally is easy to start as it requires no extra equipment. These motors are heavier than universal motors which make them an ideal solution for use on a table saw. Their weight makes them more stable and helps to reduce vibration.
Typically, an induction motor requires fewer amps per horsepower and will have a higher resale value. They are, for many, the preferred choice of motor thanks to their rugged construction and the ability to control their speed. Also, they do not require brushes as do universal motors. Because of this, they generally are easier to control.
Even microphones make use of this electromagnetic phenomenon when they take the direct vibrations of a voice and transmit them to a magnet on a spring. This generates electric waves which are amplified in speakers.
It is interesting to think of how much of electrical power is generated by spinning and moving magnets. We are able to easily transmit electric power to spinning mechanisms, which generate a larger electromagnetic force by moving a magnet in a circular motion. This phenomenon of electromagnetic force echoes the larger universal pattern of rotation of planets and the earth's own electromagnetic field.
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