What is Electric Motor ?

Electric machines come in two basic magnet field pole configurations: salient- and nonsalient-pole configurations. In the salient-

pole machine the pole's magnetic field is produced by a winding wound around the pole below the pole face. In the nonsalient-

pole, or distributed field, or round-rotor, machine, the winding is distributed in pole face slots.[60] A shaded-pole motor has a

winding around part of the pole that delays the phase of the magnetic field for that pole.

Some motors have conductors that consist of thicker metal, such as bars or sheets of metal, usually copper, alternatively aluminum. These are usually powered by

electromagnetic induction.

Commutator

A commutator is a mechanism used to switch the input of most DC machines and certain AC machines. It consists of slip-ring

segments insulated from each other and from the shaft. The motor's armature current is supplied through stationary brushes in

contact with the revolving commutator, which causes required current reversal, and applies power to the machine in an optimal

manner as the rotor rotates from pole to pole.[61][62] In absence of such current reversal, the motor would brake to a stop. In

light of improved technologies in the electronic-controller, sensorless-control, induction-motor, and permanent-magnet-motor

fields, externally-commutated induction and permanent-magnet motors are displacing electromechanically-commutated motors.

Motor supply and control

Motor supply

A DC motor is usually supplied through slip ring commutator as described above. AC motors' commutation can be either slip ring commutator or externally commutated

type, can be fixed-speed or variable-speed control type, and can be synchronous or asynchronous type. Universal motors can run on either AC or DC

Motor control

Fixed-speed controlled AC motors are provided with direct-on-line or soft-start starters.

Variable-speed controlled AC motors are provided with a range of different power inverter, variable-frequency drive or electronic commutator technologies.

The term electronic commutator is usually associated with self-commutated brushless DC motor and switched reluctance motor applications.

Major categories

Electric motors operate on three different physical principles: magnetism, electrostatics and piezoelectricity. By far, the most common is magnetism.

In magnetic motors, magnetic fields are formed in both the rotor and the stator. The product between these two fields gives rise to a force, and thus a torque on the

motor shaft. One, or both, of these fields must be made to change with the rotation of the motor. This is done by switching the poles on and off at the right time, or