Electric motor Basics -Magnetism,Electromagnetism,Rotation from magnetism

Basic motor concepts

This section will look at how motors work. The objective is to provide basic information to serve as a background for more detailed studies. We will take a look at the concepts of magnetism, AC (alternating current), electromagnetism, motor construction, and torque.

Magnetism

All magnets share two characteristics: they attract metals such as iron and steel, and they will move to point north-south if nothing obstructs them. Another very important feature of magnets is that they all have a north pole and a south pole: unlike poles attract each other, whereas like poles repel each other.

Magnetic lines of flux

We can visualise the magnetic field – the invisible force that makes magnets behave the way they do – as lines of flux moving from the north pole to the south pole. In some cases, the north and south poles are not as easily identifiable as in the classic bar or horseshoe magnets. This is certainly the case with electromagnetism.

Electromagnetism

A magnetic field is created around an electri- cal conductor when an electric current is passed through it. This is known as electromagnetism, and the physical rules for ordinary magnetism also apply here. The magnetic field moves around the conductor.

Magnetic field around a conductor     The more current, the stronger the magnetic field 

The magnetic field around electrical conductors can be strengthened by winding them into a coil around an iron core. When the wire is wound into a coil, all the flux lines produced by each turn of wire join up to form a single magnetic field around the coil. The greater the number of turns of the coil, the greater the strength of the magnetic field. This field has the same characteristics as a natural magnetic field, and so also has a north and a south pole. But before we dig any further into the world of magnetism, let us have a closer look at the main components of an electric motor: the stator and the rotor.

It possible to reverse the poles by reversing the direction of the current

Rotor:

The rotating part of the motor, rotates with the motor shaft by moving with the magnetic field of the stator.

Stator:

The stator is the stationary electrical part of the motor. It contains a number of wind-ings whose polarity is changed all the time when an alternating current (AC) is applied. This makes the combined magnetic field of the stator.

Rotation from magnetism

Quite apart from their strength, the advantage of having a magnetic field which is created by a current-carrying coil is that it makes it possible to reverse the poles of the magnet by reversing the direction of the current. This ability to reverse the poles is precisely what we use to create mechani-cal energy. What follows is a brief look at how this works.

It possible to reverse the poles by reversing the direction of the current

Opposites attract

Like poles repel each other while unlike poles attract. Simply put, this fact is used to generate constant movement of the rotor by continuously changing the polarity in the stator. You could think of the rotor as a magnet which is capable of rotating. This will keep the rotor moving in one direction, and the movement is transferred to the motor shaft. In this way, magnetism is used to convert electrical energy into mechanical energy.