The electric motors can be distinguished between them according to the type of power supply:
- Electric motors of direct current. The DC electric motor can be, in turn, a permanent induction motor or a continuous induction motor. In addition to these more general classifications there are also other more modern types of engines such as stepper motors and linear motors.
- Electric motors of alternating current. The AC motor can be classified as universal motor, synchronous motor or asynchronous motor.
The classic division is between direct current (DC) and alternating current (AC) motors. However, it is not an extremely accurate classification, since there are motors that are constructively similar to those of direct current that can also be supplied in alternating current, called universal motors. Different distinctions can be made on the basis of other references: for example, the distinction between synchronous motors, in which the power frequency is equal to a multiple of the rotation frequency, and asynchronous, in which the two frequencies are different ; Therefore, generally the categories in which the electric motor is classified are asynchronous motor, synchronous motor or DC motor.
- Synchronous motor. The synchronous motor is a type of electric motor in alternating current in which the stator, generally three-phase, generates a rotating magnetic field. In the rotor there is a magnetic field (generated by a permanent magnet or a continuous fed winding) that is attracted by the rotating magnetic field of the stator, which generates the motor torque.
- Asynchronous motor. The asynchronous motor is a type of electric motor in alternating current in which the frequency of rotation is not the same or a submultiple of the frequency of the network, that is to say, it is not "synchronous" with it; That's why it stands out from synchronous motors. The asynchronous motor is also called an induction motor due to its operating principle.
DC motor with permanent induction
The DC motor is the simplest motor. We start from the outside, where the casing or casing is, which has a fixing system to the bench or chassis, in which there is a set called stator or inductor, formed by a plate support, and magnets or electromagnets.
Further inside is the rotor, which is formed by a core of plates on an axis that supports it all surrounded by a series of windings that are connected to the deltas of the collector, which is where they receive the electric current; all this is supported by the bearings at the ends of the crankcase.
On one side of the shaft is the pulley, toothed crown or coupling, which transmit the mechanical energy to be used. When the current is passed through the brushes to the collector, an electric current is passed through the coil conductors, which creates a lateral force, and the sum of all of them gives us the torque that rotates the rotor assembly or engine. Through the collector, current is given to the appropriate coils so that this pair is as strong as possible. They are the motors that are in devices that are moved by batteries or batteries.
DC motor with variable induction
The DC motor with variable induction is the same as the motor with permanent induction, but in this case what produces the field are coils that work like an electromagnet, and are connected to the rotor in series or parallel. This motor also works with single-phase alternating current.
The most common example are the motors of normal use appliances.
Asynchronous AC motor
In the stator there are three groups of windings, which correspond to the three phases of commercial alternating current, and the rotor instead of the collector, carries three rings, which are connected to the windings of the rotor, works by the same principle, although due to the displacement between phases, a rotating field is produced, which in some way drags the rotor.
A particular case or very used construction is the squirrel cage, since it is a very simple motor, in which the deltas and windings of the rotor, are replaced by rods with rings at the ends joining the rods, hence their first name.
In asynchronous motors the windings can be connected in two ways: In star, when one end of the coils is common and the other connected to each of the phases. The other is in a triangle, when the ends of the coils are connected to each other and to a phase. The exchange of two phases causes the reversal of the direction of rotation.
It is the most commonly used engine in the industry, with the star triangle starter system.
Synchronous AC motor
Synchronous motors are so named because the rotational speed is related to the frequency of the supply current, this is due to the fact that the rotor is fed with direct current, and is dragged by the rotating field that produces the coils of the stator.
They normally carry a dynamo coupled on the same motor shaft to feed the rotor. As the speed varies with the frequency and allows to fix the torque with minimum consumption, by being coupled to an oscillator its speed can be varied very easily, and therefore it is used in traction systems (AVE - TGV).
It is fed with direct current, and the rotor contains a series of permanent magnets, which are dragged by the stator coils, which are governed by a power electronics, determining the angle of rotation, those that have proportional control, are extremely accurate in the angle of rotation, or position. These motors are used a lot in the servos of movement of the machines of numerical control, or in the engines of reading / writing of the hard disks of computer.
In a basic way it is an asynchronous motor that has been developed, so, instead of creating a rotating pair, it creates a linear displacement, by the displacement of the phases.