Basic Operation of Electric Motor

An electric motor is an electric machine that converts electrical energy into mechanical energy. An electric motor uses magnetism and electric current to operate.

There are two basic categories of electric motor namely - AC Motor and DC Motor
An electric motor is made up of two major parts namely-

1. Rotor - The rotating part of the motor. The shaft is connected to this part for rotation

2. Stator - The stationary part of the motor. The stator can be constructed of permanent magnet or an electromagnet(such as turns of conductor carrying current)

The following diagram depict the major type of electric motor we have

Magnetism

Magnetism field can be derived from two different source such as -           -   Permanent Magnet and

         -   Electromagnet

Magnetism is the force that creates rotation for a motor to operate. Recall that a permanent magnet will attract and hold magnetic materials such as iron and steel when such objects are near or in contact with the magnet. The permanent magnet is able  to do this because of its inherent magnetic force which is referred to as magnetic field

the magnetic field of a permanent bar magnet is represented by lines of flux. These lines of flux help us to visualize the magnetic field of any magnet even though they actually represent an invisible phenomenon. The number of flux lines varies from one magnetic field to another, and the stronger the magnetic field, the greater the number of lines of flux. Lines of flux are assumed to have a direction of movement from an N pole to an S pole of a magnet as shown in the diagram above.


Electromagnetism 
When a conductor such as copper, aluminium etc is supplied with a source of EMF such that current flows through the conductor, magnetic field will be created on the conductor and when the source of EMF is remove, the field will collapse.

A similar type of magnetic field is produced around a current-carrying conductor. The strength of the magnetic
field is directly proportional to the amount of current flowing through the conductor and takes the form of concentric circles around the wire. The picture below indicates the magnetic field around a straight current-carrying conductor. 

Magnetic field around a straight current carrying conductor

A relationship exists between the direction of current flow through a conductor and the direction of the magnetic field created. Known as the left-hand conductor rule, it uses electron flow from negative to positive as the basis for the current direction.
When you place your left hand so that your thumb points in the direction of the electron flow, your curled fingers point in the direction of the lines of flux that circle the conductor.  

When a current-carrying conductor is shaped into a coil, the individual flux lines produced by each of the turns form one stronger magnetic field. The magnetic field produced by a current-carrying coil resembles that of  a permanent magnet as shown below 

Magnetic field produced by a current-carrying coil

 As with the permanent magnet, these flux lines leave the north of the coil and reenter the coil at its south pole. The magnetic field of a wire coil is much greater than the magnetic field around the wire before it is formed into a coil and can be further strengthened by placing a core of iron in the center of the coil. The iron core presents less resistance to the lines of flux than the air(increasing permeability), thereby causing the field strength to increase. This is exactly how a motor stator coil is constructed: using a coil of wire with an iron core. The polarity of the poles of a coil reverses whenever the current flow through the coil reverses. Without this phenomenon, the operation of electric motors would not be possible.
Basic Principle of Operation of an Electric Motor

An electric rotor rotates as the result of the interaction of two magnetic field. One of the well known laws of the magnetism  is that like poles repel (N-N or S-S) while unlike poles attract (N-S or S-N).
To understand the operation of the motor, consider the stator been a permanent magnet comprising of N - S pole and in between it is a rotor which is a conductor current current(electromagnet).
The operation of the setup can be summarized as follow -

• The electromagnet is the moving armature part and the permanent magnet is the fixed stator part
• Like magnetic pole repel each other, causing the armature to turn

• After it turns part away around, the force of attraction between the unlike poles becomes strong enough to keep the permanent magnet rotating.
• The rotating electromagnet continues to turn until the unlike poles are lined up. At this point the rotor would normally stop because of the attraction between the unlike poles
• Commutation which is the process of reversing armature current at the moment when the unlike poles of the armature field and stator field are facing each other, thereby reversing the polarity of the armature field
• Like pole of the armature and stator field then repel each other, causing the armature rotation to continue

A current carrying conductor will generate magnetic field, and when placed in the magnetic field created by the stator, there will be an interaction between the two fields which lead to a force being experience on the conductor. The magnitude of the force on the conductor will be directly proportional to the current flowing through it. Also, a current-carrying conductor, placed in a magnetic field and at right angles to it tends to move at right angle to the field as indicated below


Types of Electric Motor
1. DC Motor
2. AC Motor

 to be continued....