Today it is impossible to imagine human civilization and a 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 the electric motor?
Appointment
The principle of operation of the electric motor and its main goals are to transfer to the working bodies the mechanical energy necessary for carrying out technological processes. The engine itself generates it due to the energy 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 they produce per unit time is called power.
Types of engines
Depending on the characteristics of the mains supply, two main types of motor can be distinguished: direct and alternating current. The most common DC machines are motors with sequential, independent and mixed excitation. Examples of AC motors can be synchronous and asynchronous machines. Despite the apparent diversity, the device and the principle of operation of an electric motor for any purpose are based on the interaction of a conductor with a current and a magnetic field or a permanent magnet (ferromagnetic object) with a magnetic field.
Frame with current - prototype of the engine
The main point in such a matter as the principle of operation of the electric motor can be called the appearance of torque. This phenomenon can be considered by the example of a frame with current, which consists of two conductors and a magnet. The current is supplied to the conductors through contact rings, which are fixed on the axis of the rotating frame. In accordance with the famous rule of the left hand on the frame will act forces that create torque about the axis. She under the action of this total force will rotate in a counterclockwise direction. It is known that this moment of rotation is directly proportional to 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 should be done to establish a permanent direction? There are two options:
- 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 operation of an AC electric motor.
Change in direction of current relative to the magnet
In order to change the direction of movement of charged particles in the conductor of the frame with the current, you need a device that would set this direction depending on the location of the conductors. This design is realized through the use of sliding contacts, which serve to supply the current frame. When replacing two with one ring, when the frame rotates half a turn, the direction of the current changes to the opposite, and the torque retains it. It is important to note that one ring is assembled from two halves that are isolated from each other.
DC machine design
The above example is the principle of operation of a DC motor. The real machine, of course, has a more complex structure, where dozens of frames are used that 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 attached to insulated rings that form a collector. A winding, collector, and core are an armature rotating in bearings on the body of the engine itself. The magnetic field of the excitation is created by the poles of permanent magnets, which are located in the housing. The winding is connected to the mains supply, and it can be switched 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 design with mixed excitation, when two types of winding connection are used at once.
Synchronous machine
The principle of operation of a synchronous electric motor is the need to create a rotating magnetic field. Then it is necessary to place in this field conductors streamlined in a constant current direction. The principle of operation of a synchronous electric motor, which has become very widespread in industry, is based on the above example with a frame with a 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, but the principle of operation of a single-phase AC motor will not differ from a three-phase one, except perhaps by the number of phases themselves, which is not essential when considering design features. The windings are placed in the grooves of the stator with a certain circumferential shift. 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 motor of the above construction. When the magnetic field interacts with the current in the rotor winding, the process of motor rotation is formed, which will be synchronous with respect to the rotation of the magnetic field formed on the stator. The synchronism will remain until the maximum moment, which is caused by the resistance, is reached. When the load increases, the machine may go out of synchronism.
Induction motor
The principle of operation of an asynchronous electric motor is the presence of a rotating magnetic field and closed frames (circuits) 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 loops, and usually have two types of execution: phase and short-circuited. The principle of operation of an alternating current electric motor is the same in both versions; only the design is changed. In the case of a squirrel-cage rotor (also known as the “squirrel cage”), the winding is filled with molten aluminum into the grooves. In the manufacture of the winding, the phase ends of each phase are brought out with the help of sliding contact rings, as this will allow the inclusion of additional resistors in the circuit that are necessary to control the speed of the motor.
Traction machine
The principle of operation of the traction motor is similar to a DC motor. From the mains supply current is supplied to the step-up transformer. Next, three-phase alternating current is transmitted to special traction substations. There is a rectifier. It converts alternating current into direct current. According to the scheme, it is drawn with one of its polarity 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, they use a chastotnik for an electric motor, the principle of which is to convert frequencies and control this characteristic.
According to the raised pantograph, voltage is supplied to the chambers where the starting rheostats and contactors are located. Using controllers, rheostats are connected to traction motors that are located on the axles of the bogies. From them, current flows through the tires to the rails, and then returns to the traction substation, thus closing the electrical circuit.