The classical set of machines represents the asynchronous induction, synchronous, DC machines, and variable reluctance machines. Among these classical machines, the asynchronous machine is most widely used in a large range of applications and is able to operate as a motor (converting electrical power into mechanical power) or as a generator (converting mechanical power into electrical power). The machine can be fed via a power electronic converter or connected directly to an AC or DC supply. Electric machines are majorly based on 4 principles. The first principle is that an electrical current produce a magnetic field around it that can be strengthened by more than a thousand times when passing through iron.

The second principle is called motor action and is defined by a force perpendicular to both the direction of the electrical current and the magnetic field. This induced force is given by:

F= i (L)

B: magnetic flux density

L= length of wire

i= magnitude of current in the wire

The third principle is that an electrical conductor moving in a magnetic field has an electrical current induced in it creating an electromotive force. The induced voltage is expressed by the following formula:

?ind= (v) L

v: velocity of the wire

L: length of conductor in the magnetic field

B: magnetic flux density

The fourth principle is that a change in the magnetic field in a circuit can cause an induced voltage to this circuit. This effect is based on the Faraday’s law that states that when a flux passes through a turn of coil, a voltage proportional to the rate of change of the flux will be induced.

?ind =

N: number of turns of wire in coils

?ind: voltage induced

F: flux passing in the coil

(http://mysite.du.edu/~jcalvert/tech/elmotors.htm)

An electric machine has two essential electrical parts: The stator and the rotor. The stator (derived from the word stationary) is the stationary part of the machine forming a hollow cylinder consisting of individual electro-magnets shaped towards the middle. The rotor (derived from the word rotating) is located inside the stator and consists of a group of electro-magnet arranged around a cylinder, mounted on the motor’s shaft with its poles facing toward the stator poles. The rotor is the rotating component of the machine.

(http://www.reliance.com/mtr/mtrthrmn.htm)

(http://www.reliance.com/mtr/mtrthrmn.htm)