The classical group of machines represents the asynchronous induction, synchronous, DC machines, and adjustable reluctance machines. Among these traditional machines, the asynchronous machine is most widely used in a big selection of applications and is able to operate as a electric motor (converting electrical power into mechanical electric power) or as a generator (changing mechanical electricity into electrical energy). The device can be fed via a electricity electronic digital converter or connected directly to an AC or DC supply. Electric machines are majorly based on 4 concepts. The first process is that an electrical current produce a magnetic field around it that can be strengthened by more than a thousand times when passing through flat iron.
The second theory is called electric motor action and it is defined with a make perpendicular to both the way of the electric current and the magnetic field. This induced pressure is distributed by:
F= i (L)
B: magnetic flux density
L= length of wire
i= magnitude of current in the wire
The third rule is that an electrical conductor moving in a magnetic field comes with an electrical current induced in it creating an electromotive force. The induced voltage is indicated by the following formula:
?ind= (v) L
v: velocity of the wire
L: amount of conductor in the magnetic field
B: magnetic flux density
The fourth rule is that a change in the magnetic field in a circuit can cause an induced voltage to this circuit. This result is based on the Faraday's law that states that when a flux moves through a turn of coil, a voltage proportional to the pace of change of the flux will be induced.
?ind =
N: volume 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 electronic parts: The stator and the rotor. The stator (produced from the term stationary) is the stationary area of the machine forming a hollow cylinder consisting of individual electro-magnets designed towards the middle. The rotor (produced from the word revolving) is situated inside the stator and contains several electro-magnet organized around a cylinder, mounted on the motor's shaft using 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)
In standard, when the change of flux is associated with mechanical motion, it is the case of electromagnetic energy conversion. In connection with the rotation machines, the voltage is produced in groups of coils, categorised as windings, by three different ways. The first strategy is by mechanised rotation of the windings by using a magnetic field, the second is mechanical rotation of the magnetic field past the winding, and third by the look of the magnetic circuit so that the reluctance varies with the rotation of the rotor. So these methods create a time-varying voltage triggered by the cyclic fee of the flux linking a particular coil. The armature winding of any machine is a combination of such coils interconnected so that their made voltage is near to the desired. Within a DC machine, the armature is the rotating member or rotor. As for the AC machine, the armature is the stationary member or stator.
The coils pointed out previously are wound on flat iron cores in order to increase the coupling between the coils, to boost the magnetic energy denseness associated with electromechanical relationship, and to form and deliver the magnetic domains in line with the requirements of each particular machine design. Eddy currents will be induced in the armature iron since it is subjected to a time varying magnetic flux. To minimize this eddy-current reduction, thin laminations for the armature of AC machines develop the armature iron. The magnetic circuit is completed through the flat iron of the other machine member, and excitation coils, or field windings, may be located on that member to act as the principal way to obtain flux. Permanent magnets may be used in small machines, and improvements in permanent magnet technology are leading to their use in bigger machines. In varying reluctance machines, there are no windings on the rotor, and the procedure is determined by the non uniformity of air-gap reluctance associated with modifications in rotor position.
(electric equipment fifth edition (Collection))
AC electric machines
AC machines are motors transforming AC electricity to mechanical energy and generators that convert mechanical to AC electrical energy. AC electric machines are divided into two types: Asynchronous (induction) and synchronous machines. The difference between these two types is the fact induction machines have their field currents supplied by magnetic induction as the field current in synchronous ones are given by another DC source.
(Electric machinery basics).
The principle of rotating magnetic areas is the main rule of the operation to many ac motors. The magnetic field created by the poles will make the rotor rotate making the stator poles gradually change. This change can make the rotor follow and rotate with the magnetic field of the stator. As each change is made, the poles of the rotor are enticed by the contrary poles on the stator, forcing the rotor to rotate with the stator field.
(http://www. reliance. com/mtr/mtrthrmn. htm)
The rotor is spinning within the stator at angular velocity ?n, the magnitude of the flux density vector B at any viewpoint a about the stator is distributed by B= BM cos(?t-a). Then the voltage induced in the stator that has N changes of wire is indicated by eind= NF?cos(?t).
The voltage induced is sinusoidal with amplitude depending on flux, angular speed and a constant with regards to the construction of the device.
In a three period set of coils, the voltages induced will have same magnitude but they are shifted by 120 levels.
eaa'(t)= NF? sin(?t)
ebb'(t)= NF? sin(?t-120)
ecc'(t)= NF? sin(?t-240)
The rms voltage of each stage is: EA= pNFf
