Electric+Motor

Electric Motor

Electric motors are everywhere! In your house, almost every mechanical movement that you see around you is caused by an AC (alternating current) or DC (direct current) electric motor. First of all, lets be clear on what exactly an electric motor is: **An electric motor is a device that uses an electric current to turn an axle. An electric motor transforms electrical energy into mechanical energy.** As I mentioned before: there are two main types of motors: The Alternative Current (AC) motors and the Direct Current (DC) motors. Both AC motors and DC motors have several shapes and sizes. Many of them are standardized electric motors daily life's applications, and other electric motors are intended for specific tasks. The first and most important step in electric motor selection is determining load characteristics -- torque and speed versus time. A motor is essentially composed of an armature, wire, wrapped around a ferromagnetic core, a source of energy, a commutator, brushes and permanent magnets. The generators operate on the same principle but in reverse: They provide rotational speed and one recovers a stream across the winding.

• ** AC motors: ** The most common and simple industrial motor is the three phase AC induction motor, sometimes known as the "squirrel cage" motor. • The speed of the AC motor depends only on three variables: 1. The fixed number of winding sets (known as poles) built into the motor, which determines the motor's base speed. 2. The AC line voltage's frequency. Variable speed drives change this frequency to change the speed of the motor. 3. The amount of torque loading on the motor, which causes slip. • The AC motor has the advantage of being the __lowest cost motor__ for applications requiring more than about 1/2 hp (325 watts) of power. This is due to the simple design of the motor. For this reason, AC motors are overwhelmingly preferred for fixed speed applications in industrial applications and for commercial and domestic applications where AC line power can be easily attached. • Over 90% of all motors are AC induction motors. They are found in air conditioners, washers, dryers, industrial machinery, fans, blowers, vacuum cleaners, and many, many other applications. • ** DC motors: ** The brushed DC motor is one of the earliest motor designs. Today, it is the motor of choice in the majority of variable speed and torque control applications. They have many advantages too: they are easy to understand design, can control speed simply, can also easily control the torque and have a cheap drive design. But they also have many disadvantages: they are expensive to produce, is hard to control at lowest speed, is larger than the AC motor, requires a high maintenance and creates dust.

__ Energy conversions: __ An electric motor transforms electrical energy into mechanical energy.

__ How does a motor work: __ In a motor, current is reversed just as the loop, or armature, gets to the vertical position, which reverses the direction of the movement of both sides of the loop. o The side of the loop that moved up on the left now moves down on the right o The side of the loop that moved down on the right now moves up on the left

Parts and function: 1) __ Brushes: __

__ o __ There are distinguished basically 3 types of carbon brushes:


 * 1) brushes for automotive applications: DC current, voltage 12-48 V
 * 2) brushes for household applications: AC current, voltage 110 / 220 V
 * 3) brushes for industrial motors: both AC and DC current, various voltages

o The brushes that touch the commutator conduct current to the armature o The brushes do not move o Because the brushes conduct the current, changing brushes reverses the direction of the current of in the armature

2) __ Armature: __  o The current is in opposite directions on each side of the armature causing one side to move up while the other side moves down.    o The direction of current reverses with each half turn so the armature spins continuously    o As the armature rotates, each part of the commutator contacts one brush and then the other

3) __ Commutator: __  o It is a ring split in half    o Each half is attached to the ring of the armature    o The commutator rotates with the armature, repeatedly reversing the flow of current    o Both the commutator and the armature rotate at the same time    o As it moves, it passes through the brushes    o Each of its half is connected to the current source by one of the brushes