Today it is impossible to imagine human civilization and high-tech society without electricity. One of the main devices that ensure the operation of electrical appliances is the engine. This machine has found the widest distribution: from industry (fans, crushers, compressors) to domestic use (washing machines, drills, etc.). But what is the principle of operation of an electric motor?
Destination
The principle of operation of the electric motor and its main goals are to transfer the mechanical energy necessary for the performance of technological processes to the working bodies. The engine itself generates it due to the electricity consumed from the network. In essence, the principle of operation of an electric motor is to convert electrical energy into mechanical energy. The amount of mechanical energy generated by it in one unit of time is called power.
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Depending on the characteristics of the supply network, two main types of motor can be distinguished: direct and alternating current. The most common DC machines are motors with series, independent and mixed excitation. Examples of AC motors are synchronous and asynchronous machines. Despite the apparent diversity, the device and principle of operation of an electric motor for any purpose are based on the interaction of a conductor with current and a magnetic field, or a permanent magnet (ferromagnetic object) with a magnetic field.
Current loop - a prototype of the engine
The main point in such a matter as the principle of operation of an electric motor can be called the appearance of torque. This phenomenon can be considered using the example of a frame with a current, which consists of two conductors and a magnet. Current is supplied to the conductors through contact rings, which are fixed on the axis of the rotating frame. In accordance with the famous left-hand rule, forces will act on the frame, which will create a torque about the axis. It will rotate counterclockwise under the action of this total force. It is known that this moment of rotation is directly proportional to the magnetic induction (B), current strength (I), frame area (S) and depends on the angle between the field lines and the axis of the latter. However, under the action of a moment that changes in its direction, the frame will oscillate. What can be done to create a permanentdirections? There are two options here:
- change the direction of the electric current in the frame and the position of the conductors relative to the poles of the magnet;
- change the direction of the field itself, while the frame rotates in the same direction.
The first option is used for DC motors. And the second is the principle of the AC motor.
Changing the direction of the current relative to the magnet
In order to change the direction of movement of charged particles in the conductor of the frame with current, you need a device that would set this direction depending on the location of the conductors. This design is implemented through the use of sliding contacts, which serve to supply current to the loop. When one ring replaces two, when the frame rotates half a turn, the direction of the current is reversed, and the torque retains it. It is important to note that one ring is assembled from two halves, which are isolated from each other.
DC machine design
The above example is the working principle of a DC motor. The real machine, of course, has a more complex design, where dozens of frames are used to form the armature winding. The conductors of this winding are placed in special grooves in a cylindrical ferromagnetic core. The ends of the windings are connected to insulated rings which form a collector. The winding, commutator and core are the armature rotating in bearings on the body of the motor itself. The excitation magnetic field is created by the poles of permanent magnets, which are located in the housing. The winding is connected to the mains, and it can be turned on either independently of the armature circuit or in series. In the first case, the electric motor will have independent excitation, in the second - sequential. There is also a mixed excitation design, when two types of winding connection are used at once.
Synchronous machine
The principle of operation of a synchronous motor is to create a rotating magnetic field. Then you need to place in this field the conductors flowed around with a constant current in the direction. The principle of operation of a synchronous motor, which has become very widespread in industry, is based on the above example with a loop with current. The rotating field created by the magnet is formed using a system of windings that are connected to the mains. Three-phase windings are usually used, however, the principle of operation of a single-phase AC motor will not differ from a three-phase one, except perhaps in the number of phases themselves, which is not significant when considering design features. The windings are placed in the stator slots with some shift around the circumference. This is done to create a rotating magnetic field in the formed air gap.
Synchronism
A very important point is the synchronous operation of the electric motorthe above construction. When the magnetic field interacts with the current in the rotor winding, the process of motor rotation itself is formed, which will be synchronous with respect to the rotation of the magnetic field formed on the stator. Synchronism will be maintained until the maximum torque is reached, which is caused by resistance. If the load increases, the machine may get out of sync.
Induction motor
The principle of operation of an asynchronous electric motor is the presence of a rotating magnetic field and closed frames (contours) on the rotor - the rotating part. The magnetic field is formed in the same way as in a synchronous motor - with the help of windings located in the grooves of the stator, which are connected to an alternating voltage network. The rotor windings consist of a dozen closed loop-frames and usually have two types of execution: phase and short-circuited. The principle of operation of the AC motor in both versions is the same, only the design changes. In the case of a squirrel-cage rotor (also known as a squirrel cage), the winding is poured with molten aluminum into the slots. In the manufacture of the phase winding, the ends of each phase are brought out using sliding contact rings, as this will allow additional resistors to be included in the circuit, which are necessary to control the engine speed.
Traction machine
The principle of operation of the traction motor is similar to that of a DC motor. From the supply network, current is supplied to a step-up transformer. Furtherthree-phase alternating current is transmitted to special traction substations. There is a rectifier. It converts AC to DC. According to the scheme, it is carried out with one of its polarities to the contact wires, the second - directly to the rails. It must be remembered that many traction mechanisms operate at a frequency different from the established industrial (50 Hz). Therefore, a frequency converter is used for an electric motor, the principle of operation of which is to convert frequencies and control this characteristic.
At the raised pantograph, voltage is supplied to the chambers where the starting rheostats and contactors are located. With the help of controllers, the rheostats are connected to traction motors, which are located on the axles of the bogies. From them, the current flows through the tires to the rails, and then returns to the traction substation, thus completing the electrical circuit.
