What is Electric Motor ?

mechanical force will occur in a constant direction of rotation

Operating at normal power line frequencies, universal motors are often found in a range less than 1000 watts. Universal motors

also formed the basis of the traditional railway traction motor in electric railways. In this application, the use of AC to power a

motor originally designed to run on DC would lead to efficiency losses due to eddy current heating of their magnetic

components, particularly the motor field pole-pieces that, for DC, would have used solid (un-laminated) iron and they are now

rarely used.

An advantage of the universal motor is that AC supplies may be used on motors that have some characteristics more common

in DC motors, specifically high starting torque and very compact design if high running speeds are used. The negative aspect is

the maintenance and short life problems caused by the commutator. Such motors are used in devices, such as food mixers and

power tools, that are used only intermittently, and often have high starting-torque demands. Multiple taps on the field coil

provide (imprecise) stepped speed control. Household blenders that advertise many speeds frequently combine a field coil with

provide (imprecise) stepped speed control. Household blenders that advertise many speeds frequently combine a field coil with

several taps and a diode that can be inserted in series with the motor (causing the motor to run on half-wave rectified AC).

Universal motors also lend themselves to electronic speed control and, as such, are an ideal choice for devices like domestic

washing machines. The motor can be used to agitate the drum (both forwards and in reverse) by switching the field winding

with respect to the armature.

Whereas SCIMs cannot turn a shaft faster than allowed by the power line frequency, universal motors can run at much higher

speeds. This makes them useful for appliances such as blenders, vacuum cleaners, and hair dryers where high speed and light weight are desirable. They are also

commonly used in portable power tools, such as drills, sanders, circular and jig saws, where the motor's characteristics work well. Many vacuum cleaner and weed

trimmer motors exceed 10,000 rpm, while many similar miniature grinders exceed 30,000 rpm.

Externally commutated AC machine

The design of AC induction and synchronous motors is optimized for operation on single-phase or polyphase sinusoidal or quasi-sinusoidal waveform power such as

supplied for fixed-speed application from the AC power grid or for variable-speed application from VFD controllers. An AC motor has two parts: a stationary stator

having coils supplied with AC to produce a rotating magnetic field, and a rotor attached to the output shaft that is given a torque by the rotating field.

Induction motor