The electric motor is installed on something. Types of electric motors: design, principle of operation

Electric motor converts electricity into energy mechanical movement. As well as electric generator an electric motor usually consists of a stator and a rotor, referring to rotating electrical machines. However, motors are produced in which the moving part performs a linear (usually rectilinear movement(linear motors).

The most common type of electric motor is three-phase squirrel-cage asynchronous motor the design principle of which is shown in Fig. 1, the rotor winding of this motor is a system of massive copper or aluminum rods placed parallel to each other in the grooves of the rotor, the ends of which are connected to each other by short-circuited rings.

Rice. 1. The principle of the design of a squirrel-cage asynchronous motor.
1 - stator, 2 - rotor, 3 - shaft, 4 - housing

When aluminum is used, the entire winding (squirrel cage) is usually formed by injection molding. The rotating magnetic field of the stator induces a current in the rotor winding, the interaction of which with the magnetic field of the stator causes the rotor to rotate. The rotor rotation speed is always less than magnetic field stator and its relative difference with the speed of rotation of the stator magnetic field (with synchronous speed) is called slip. This value depends on the load on the motor shaft and is usually 3... 5% at full load. For stepwise speed control, a stator winding with a switchable number of poles can be used; for example, two three- and four-speed asynchronous motors can be made using this principle. For smooth speed control, the motor is usually powered through an adjustable frequency converter.

For the main control of the speed of an asynchronous motor below the rated one, previously, instead of squirrel-cage motors, motors with a wound rotor were used, in which the rotor winding has the same three-phase design as the stator winding. Such a winding is connected through slip rings located on the motor shaft with an adjusting rheostat where part of the energy consumed by the motor is converted into heat. Regulation therefore occurs at the expense of reducing engine efficiency and is currently rarely used.

Squirrel-cage asynchronous motors characterized by their compactness and high reliability, as well as a much longer service life than engines internal combustion. They are usually smaller in size and lighter in weight than internal combustion engines of the same power. They can be manufactured in a very wide range of nominal powers from several watts to several tens of megawatts. Low power motors (up to several hundred watts can be single-phase.

Synchronous motors are designed in the same way as synchronous generators. At a constant network frequency, they rotate at a constant speed regardless of the load. Their advantage over asynchronous motors is that they do not consume reactive energy from the network, but can supply it to the network, thereby covering the consumption of reactive energy by other electrical receivers. Synchronous motors are not suitable for frequent starts and are mainly used for relatively stable mechanical loads and when a constant rotation speed is required.

DC motors used when smooth speed control is necessary. This is achieved by changing the armature and/or excitation current using semiconductor devices (formerly by means of control rheostats) or by changing the supply voltage. Since nowadays it is easy and without a significant change in efficiency (using frequency converters) to smoothly regulate the speed of AC motors, DC motors, due to their higher cost, large sizes and additional losses arising during regulation began to be used much less frequently than before.
Stepper motors are driven by voltage pulses. With each pulse, the motor rotor rotates through a certain angle (for example, several degrees). Such motors are used in low-speed mechanisms that usually require precise positioning. For example, engines can be manufactured that make one revolution per day or even per year.

Linear motors used for linear motion when converting rotating motion into linear motion using mechanical gears or other devices is impossible or unacceptable. The most commonly used are induction linear motors, but there are also synchronous and stepper linear motors and even DC motors.

The main advantages of electric motors over internal combustion engines can be considered
- smaller dimensions, lighter weight and lower cost,
- much higher efficiency (usually 90..95%),
- better adjustability (usually maintaining high efficiency),
- high reliability and long service life,
- less noise and vibration during operation,
- quick and trouble-free (if necessary - smooth) start-up,
- much simpler operation,
- no fuel consumption and, as a result, no emissions of combustion products into the environment,
- easy connection to any working machines and mechanisms.
The use of electric motors can be problematic when they must be placed on portable and mobile devices or on Vehicle Oh. For power supply in such cases, they can be used, depending on the range and nature of movement,
- flexible cables,
- contact wires or contact bars,
- power sources placed on mobile vehicles (batteries, fuel cells, engine generators, etc.).

In many cases, these power methods limit the maneuverability or range of vehicles (especially cars) or other mobile machinery to such an extent that the use of internal combustion engines remains more rational. The first electric motor was not electromagnetic, but electrostatic, and it was made in 1748 by the publisher and public figure city of Philadelphia (Philadelphia, USA) Benjamin Franklin (1706-1790). The rotor of this engine was a toothed disk, the teeth of which were subject to impulse forces of attraction and repulsion caused by electrostatic discharges; the disk made 12...15 revolutions per minute and could carry up to 100 silver coins. The first electromagnetic motors (devices in which either a conductor through which current flowed rotated around a bar magnet (Fig. 2), while doing work - mixing mercury, or a bar magnet rotated around a conductor with current, were invented in 1821 by an assistant at the Royal Institution of London (Royal Institution) Michael Faraday.

Rice. 2. The principle of construction of Michael Faraday's experimental device for demonstrating electric rotation.
1 - rotating metal rod, 2 - bar magnet, 3 - glass or porcelain vessel, 4 - mercury, 5 - seal, i - current

The first (oscillating) engine, which, in principle, could be connected to a driven working machine, was made in 1831 by Joseph Henry (1797-1878), a mathematics and natural history teacher at the Albany Boys School (Albany, USA); The design principle of this engine is shown in Fig. 3.

Rice. 3. The design principle of Joseph Henry's oscillating electric motor.
1 - permanent magnets, 2 - swinging electromagnet, 3 - shaft, 4 - mercury contacts.

After the Henry engine, several different experimental reciprocating electric motors were created. The first rotating electric motor was created for the purpose of real application on April 8, 1834 by the inspector of the port of Pillau rPiilau, East Prussia), civil engineer Moritz Hermann Jacobi (Moritz Hermann Jacobi. 1801-1874), who independently studied electrical engineering in the library and laboratories of the University of Königsberg. An eight-pole motor, in which both the stator and the rotor consisted of four horseshoe-shaped electromagnets and which made 80 ... 120 revolutions per minute, received power from a battery of galvanic cells with a voltage of 6V. Its shaft power was approximately 15 W and its efficiency was about 13%. Jacobi researched and improved his engine, among other things, at the University of Tartu, where he was elected professor of civil architecture in 1835.

Moritz Hermann (later, in Russia - Boris Semenovich) Jacobi was born in 1801 in Potsdam (Potsdam, Germany) into a wealthy family and received a good education at home; already in his youth he was equally fluent in German, English and French languages and also knew Latin and Ancient Greek very well. In 1828, he graduated from the University of Göttingen (Gottingen Germany) with a qualification as an architect, then worked in road construction, and in 1833 he moved to Königsberg, where he younger brother Carl Gustav Jacob Jacobi (1804-1851) was a professor of mathematics. He began working as an inspector at the port of Pillau and attending the University of Königsberg to acquire knowledge in electrical engineering. In 1834 he built the above-mentioned engine, and in 1835, on the initiative of Friedrich Georg Wilhelm Struve, professor of astronomy at the University of Tartu (1793-1864), he was elected professor of civil architecture at this university. His engine aroused interest in St. Petersburg, and in 1837 Jacobi was seconded to the capital's Academy of Sciences to develop electric drives for warships, remaining officially in the service of the University of Tartu until 1840. In 1838, Jacobi tested the world's first electric drive with a rotating engine (installed on a sea boat) on the Neva, but further research showed that, unfortunately, there was no technically and economically suitable source of energy to power the drive.

In 1839, Jacobi was elected a corresponding member, and in 1842 - a member of the Academy of Sciences and subsequently worked mainly on the development of electromagnetic telegraphs, electroplating and metrology. He repeatedly met with Michael Faraday, famous French and German physicists of that time.

In the mid-19th century, several more varieties of DC motors were developed, but their practical use was hampered by low power and, as Jacobi had already established, insufficient economic efficiency power sources of that time - galvanic cells and primitive electric machine generators. Wider use of electric motors became possible only in 1866 after the advent of self-excited direct current generators.

After the advent of the multiphase AC system, the German company AEG began to explore the possibilities of using asynchronous motors, invented by its chief engineer Mikhail Dolivo-Dobrowolsky (in German, Michael von Dolivo-Dobrowolsky) and submitted on March 8, 1889 an application for patenting a squirrel-cage asynchronous motor. After this, reliable and highly efficient AC motors began to be widely used. Currently, all the above-mentioned electric motors have reached a very high technical level and are widest application in stationary installations, and in Lately increasingly in vehicles.

The electric motor is one of the key inventions of mankind. It is thanks to electric motors that we managed to achieve such a high development of our civilization. The basic principles of operation of this device are studied at school. A modern electric motor can perform many different tasks. Its operation is based on the transmission of rotation of the electric drive shaft to other types of movement. In this article we will take a closer look at how this device works.

Characteristics of electric motors

An electric motor is essentially a device through which electrical energy is converted into mechanical energy. This phenomenon is based on magnetism. Accordingly, the design of the electric motor includes permanent magnets and electric magnets, as well as various other materials that have attractive properties. Today this device is used almost everywhere. For example, an electric motor is a key part of watches, washing machines, air conditioners, mixers, hair dryers, fans, air conditioners and other household appliances. There are countless options for using an electric motor in industry. Their sizes also vary from the head of a match to the engine on trains.

Types of electric motors

Currently, many types of electric motors are produced, which are divided according to the type of design and power supply.

According to power supply principle All models can be divided into:

AC devices that use the electrical network as power;
DC devices powered by power supplies, AA batteries, rechargeable batteries and other similar sources.

According to the mechanism of operation all electric motors are divided into:

synchronous, having rotor windings and a brush mechanism used to supply electric current to the windings;
asynchronous, characterized by a simpler design without brushes and rotor windings.

The operating principle of these electric motors is significantly different. A synchronous motor rotates at the same speed as the magnetic field that rotates it. At the same time, an asynchronous motor rotates at a lower speed than the electromagnetic field.

Motor classes (varies depending on the current used) :

class AC (Alternating Current) - operates from an alternating current source;
class DC (Direct Current) - uses direct current for operation;
a universal class that can use any current source for operation.

In addition, electric motors may differ not only in the type of design, but also in the methods of controlling the speed of rotation. At the same time, all devices, regardless of type, use the same conversion principle electrical energy to mechanical.

The principle of operation of the unit on direct current

This type of electric motor works based on a principle developed by Michael Faraday back in 1821. His discovery is that when an electrical impulse interacts with a magnet, there is a possibility of permanent rotation. That is, if you mark a vertical frame in a magnetic field and pass along it electricity, then an electromagnetic field may arise around the conductor. It will be in direct contact with the poles of the magnets. It turns out that the frame will be attracted to one of the magnets and repelled from the other. Accordingly, it will turn from a vertical position to a horizontal one, in which the influence of the magnetic field on the conductor will be zero. It turns out that in order to continue the movement, it will be necessary to supplement the structure with another frame at an angle or change the direction of the current in the first frame. In most devices, this is achieved by two half-rings, to which contact plates from the battery are attached. They promote a rapid change in polarity, causing movement to continue.

Modern electric motors do not have permanent magnets, since their place is taken by electric magnets and inductors. That is, if you disassemble any such engine, you will see turns of wire coated with an insulating compound. In fact, they are an electromagnet, which is also called an excitation winding. Permanent magnets in the design of electric motors are used only in small children's toys powered by AA batteries. All other more powerful electric motors are equipped only with electric magnets or windings. At the same time, the rotating part is called the rotor, and the static part is called the stator.

How does an asynchronous electric motor work?

The housing of an asynchronous motor contains stator windings, which create a rotating magnetic field. The ends for connecting the windings are brought out through a special terminal block. Cooling is carried out by a fan located on the shaft at the end of the electric motor. The rotor is tightly connected to a shaft made of metal rods. These short-circuited rods are connected to each other on both sides. Due to this design, the motor does not require periodic maintenance, since there is no need to change the current supply brushes from time to time. That is why asynchronous motors are considered more reliable and durable than synchronous ones. The main cause of failure of asynchronous motors is wear of the bearings on which the shaft rotates.

For asynchronous motors to operate, it is necessary that the rotor rotates slower than the rotation of the electromagnetic field of the stator. It is due to this that an electric current arises in the rotor. If the rotation were carried out at the same speed, then, according to the law of induction, an EMF would not be formed, and there would be no rotation as a whole. However, in real life Due to bearing friction and increased load on the shaft, the rotor will spin more slowly. Magnetic poles rotate regularly in the rotor windings, due to which the direction of the current in the rotor constantly changes.

A circular saw also works on the same principle, since it reaches its highest speed without load. When the saw begins to cut the board, its rotation speed decreases and at the same time the rotor begins to rotate more slowly in relation to the electromagnetic field. Accordingly, according to the laws of electrical engineering, an even greater value of EMF begins to arise in it. After this, the current consumed by the motor increases and it begins to operate at full power. At a load at which the motor stalls, destruction of the squirrel-cage rotor may occur. This occurs due to the fact that the maximum value of EMF occurs in the motor. That is why it is necessary to select an electric motor of the required power. If you use an engine with too much power, this can lead to unnecessary energy consumption.

The speed at which the rotor rotates in this case depends on the number of poles. If the device has two poles, then the rotation speed will correspond to the rotation speed of the magnetic field. The maximum asynchronous electric motor can develop up to 3 thousand revolutions per second. The network frequency can be up to 50 Hz. To reduce the speed by half you will have to increase the number of poles in the stator to 4 and so on. The only drawback of asynchronous motors is that they can only be adjusted by changing the frequency of the electric current. In addition, in an asynchronous motor you will not be able to achieve a constant shaft speed.

How does an AC synchronous electric motor work?

A synchronous electric motor is used in cases where a constant rotation speed and the ability to quickly adjust it are required. In addition, a synchronous motor is used where it is necessary to achieve a rotation speed of more than 3 thousand revolutions, which is the limit for an asynchronous motor. Therefore, this type of electric motor is advantageously used in household appliances, such as vacuum cleaner, electric tools, washing machine and so on.

The housing of an AC synchronous motor contains windings that are wound around the armature and rotor. Their contacts are soldered to the sectors of the current collector and ring, to which voltage is applied using graphite brushes. The terminals here are arranged so that the brushes always supply voltage to only one pair. Among the disadvantages of a synchronous motor, one can note their lower reliability compared to asynchronous motors.

The most common breakdowns of synchronous motors:

Premature wear of the brushes or poor contact due to weakening of the spring.
Contamination of the collector, which can be cleaned with alcohol or fine sandpaper.
Bearing wear.

Operating principle of a synchronous motor

The torque in such an electric motor is created by the interaction between the magnetic field and the armature current, which are in contact with each other in the field winding. As the alternating current is directed, the direction of the magnetic flux will also change, which ensures rotation in only one direction. The rotation speed is adjusted by changing the strength of the applied voltage. Changing the voltage rate is most often used in vacuum cleaners and drills, where a variable resistance or rheostat is used for this purpose.

Mechanism of operation of individual engine types

Industrial electric motors can operate on both direct and alternating current. Their design is based on a stator, which is an electromagnet that creates a magnetic field. An industrial electric motor contains windings that are alternately connected to a power source using brushes. They alternately turn the rotor at a certain angle, which sets it in motion.

The simplest electric motor for children's toys can only operate using direct current. That is, it can receive current from a AA battery or accumulator. In this case, the current passes through a frame located between the poles of a permanent magnet. Due to the interaction of the magnetic fields of the frame with the magnet, it begins to rotate. At the completion of each half-turn, the collector switches the contacts in the frame that go to the battery. As a result, the frame performs rotational movements.

Thus, today there is a large number of electric motors for various purposes, which have one operating principle.

An electric motor is an electric machine that converts electrical energy into mechanical energy. Typically, an electric machine performs mechanical work by consuming electrical energy applied to it, which is converted into rotational motion. There are also linear motors in technology that can immediately create translational motion of the working body.

Design features and principle of operation

It doesn't matter which design, but the design of any electric motors is the same. The rotor and stator are located inside a cylindrical groove. The rotation of the rotor is excited by a magnetic field that repels its poles from the stator (stationary winding). Constant repulsion can be maintained by reconnecting the rotor windings, or by forming a rotating magnetic field directly in the stator. The first method is inherent in commutator electric motors, and the second - in asynchronous three-phase motors.

The housing of any electric motor is usually cast iron or made of aluminum alloy. Motors of the same type, despite the housing design, are produced with the same installation dimensions and electrical parameters.

The operation of the electric motor is based on the principles electromagnetic induction. Magnetic and electrical energy create an electromotive force in a closed circuit that conducts current. This property is inherent in the operation of any electric machine.

A moving electric current in the middle of a magnetic field is constantly affected by mechanical force, rapidly trying to deflect the direction of charges perpendicular to the force magnetic lines plane. During the passage of electric current through a metal conductor or coil, mechanical force strives to move or rotate the entire winding and each current conductor.

Purpose and application of electric motors

Electrical machines have many functions; they are capable of amplifying the power of electrical signals, converting voltage values or alternating current into direct current, etc. To perform such different actions There are various types of electric machines. An engine is a type of electrical machine designed to convert energy. Namely, this type of device converts electrical energy into motive force or mechanical work.

It is in great demand in many industries. They are widely used in industry, on machines for various purposes and in other installations. In mechanical engineering, for example, earthmoving and lifting machines. They are also common in the areas National economy and household appliances.

Classification of electric motors

An electric motor is a type of electric machine according to:

Specifics of the generated torque:
hysteresis;
magnetoelectric.
Fastening structure:
with a horizontal shaft arrangement;
with vertical shaft placement.
Action protection external environment:
protected;
closed;
explosion-proof.

In hysteresis devices, torque is generated by rotor magnetization reversal or hysteresis (saturation). These engines are little used in industry and are not considered traditional. Magnetoelectric motors are in demand. There are many modifications of these engines.

They are divided into large groups according to the type of current flowing:

Direct current.
Alternating current.
Universal motors (operate on direct alternating current).

Features of magnetoelectric DC motors

Using DC motors, adjustable electric drives with high performance and dynamic performance are created.

Types of electric motors:

With electromagnets.
With permanent magnets.

The group of electric motors powered by direct current is divided into subtypes:

Collector . These electrical appliances contain a brush-commutator unit that provides electrical connection between the stationary and rotating parts of the engine. Devices come with self-excitation and independent excitation from permanent magnets and electromagnets.
The following types of self-excitation of motors are distinguished:
parallel;
sequential;
mixed.
Collector devices have several disadvantages:
Low reliability of devices.
The brush-commutator unit is a rather difficult to maintain component of a magnetoelectric motor.
Collectorless (valve) . These are closed-loop motors that operate on a similar principle to synchronous devices. Equipped with a rotor position sensor, a coordinate converter, as well as an inverter and a power semiconductor converter.

These machines are produced in various sizes from the smallest low-voltage to huge sizes (mostly up to megawatt). Miniature electric motors are used in computers, phones, toys, cordless power tools, etc.

Applications, pros and cons of DC motors

DC electric machines are used in various fields. They are used to equip lifting and transport, paint and finishing production machines, as well as polymer and paper production equipment, etc. Often, an electric motor of this type is built into drilling rigs, auxiliary units of excavators and other types of electric vehicles.

Advantages of electric motors:

Ease of control and speed regulation.
Simplicity of design.
Excellent starting properties.
Compactness.
Possibility of operation in different modes (motor and generator).

Disadvantages of engines:

Commutator motors require difficult preventive maintenance of brush-commutator units.
High cost of production.
Collector devices have no long term service due to wear and tear of the collector itself.

AC motor

In AC electric motors, the electric current is described according to a sinusoidal harmonic law, periodically changing its sign (direction).

The stator of these devices is made of ferromagnetic plates having slots for placing winding turns in them with a coil configuration.

Electric motors are classified according to their operating principle synchronous and asynchronous . Their main difference is that the speed of the stator magnetomotive force in synchronous devices is equal to the speed of rotation of the rotor, but in asynchronous motors these speeds do not coincide; usually the rotor rotates slower than the field.

Synchronous motor

Due to the identical (synchronous) rotation of the rotor with the magnetic field, the devices are called synchronous electric motors. They are divided into subspecies:

Reactive.
Stepper.
Reactive-hysteresis.
With permanent magnets.
With field windings.
Valve reactive.
Hybrid reluctance synchronous motor.

Most of computer equipment equipped with stepper motors. Energy conversion in these devices is based on discrete angular movement of the rotor. Stepper motors have high productivity, regardless of their tiny size.

Advantages of synchronous motors:

Stable rotation speed, which does not depend on mechanical loads on the shaft.
Low sensitivity to voltage surges.
Can act as a power generator.
Reduce the consumption of power provided by power plants.

Disadvantages in synchronous devices:

Difficulty starting.
Complexity of design.
Difficulty in adjusting the rotation speed.

The disadvantages of a synchronous motor make an asynchronous type electric motor more profitable to use. However, most synchronous motors, due to their constant speed operation, are in demand for installations in compressors, generators, pumps, as well as large fans and other equipment.

Asynchronous electric motor

The stator of asynchronous motors represents a distributed two-phase, three-phase, or less often multiphase winding. The rotor is made in the form of a cylinder using copper, aluminum or metal. Its grooves contain either pressed conductive conductors to the axis of rotation at a certain angle. They are connected into one unit at the ends of the rotor. The countercurrent is excited in the rotor by the alternating magnetic field of the stator.

Based on their design features, there are two types of asynchronous motors:

With wound rotor.
With squirrel-cage rotor.

Otherwise, the design of the devices is no different; their stator is absolutely the same. Based on the number of windings, the following electric motors are distinguished:

Single-phase. This type of engine does not start on its own; it requires a starting push. For this, a starting winding or a phase-shifting circuit is used. The devices are also started manually.
Two-phase. These devices contain two windings with phases shifted by an angle. A rotating magnetic field appears in the device, the intensity of which increases at the poles of one winding and simultaneously decreases in the other.
A two-phase electric motor can start on its own, but there are difficulties with reverse. Often this type of device is connected to single-phase networks, including the second phase through a capacitor.
Three-phase. The advantage of these types of electric motors is easy reverse. The main parts of the engine are a stator with three windings and a rotor. Allows you to smoothly adjust the rotor speed. These devices are quite in demand in industry and technology.
Polyphase . These devices consist of a built-in multiphase winding in the stator slots on its inner surface. These engines guarantee high operational reliability and are considered advanced engine models.

Asynchronous electric motors greatly facilitate people's work, so they are indispensable in many areas.

The advantages of these devices, which played a role in their popularity, are the following:

Ease of production.
High reliability.
They do not require converters to be connected to the network.
Low operating costs.

To all this, you can add the relative cost of asynchronous devices. But they also have disadvantages:

Low power factor.
Difficulty in accurately adjusting speed.
A small starting point.
Dependence on network voltage.

But thanks to powering the electric motor using a frequency converter, some of the device’s shortcomings are eliminated. Therefore, the need for asynchronous motors does not decrease. They are used in drives of various machine tools in the fields of metalworking, woodworking, etc. They are needed by weaving, sewing, earthmoving, lifting and other types of machines, as well as fans, pumps, centrifuges, various power tools and household appliances.

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 is widely used: from industry (fans, crushers, compressors) to household use (washing machines, drills, etc.). But what is the operating principle of an electric motor?

Purpose

The principle of operation of the electric motor and its main goals are to transfer to the working bodies the necessary technological processes mechanical energy. The engine itself produces it using electricity consumed from the network. Essentially speaking, the operating principle of an electric motor is to convert electrical energy into mechanical energy. The amount of mechanical energy it produces in one unit of time is called power.

Types of engines

Depending on the characteristics of the supply network, two main types of motor can be distinguished: direct current and alternating current. The most common are motors with sequential, independent and mixed excitation. Examples of motors include synchronous and asynchronous machines. Despite the apparent diversity, the design and operating principle 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.

Frame with current - 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 current-carrying frame, which consists of two conductors and a magnet. Current is supplied to the conductors through slip rings, which are attached to the axis of the rotating frame. In accordance with the famous left-hand rule, forces will act on the frame that will create a torque about the axis. Under the influence of this total force, it will rotate in a counterclockwise direction. It is known that this torque is directly proportional to the magnetic induction (B), (I), the area of the frame (S) and depends on the angle between the field lines and the axis of the latter. However, under the influence of a moment changing in its direction, the frame will make oscillatory movements. What should be done to form a permanent direction? 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, despite the fact that the frame rotates in the same direction.

The first option is used for DC motors. And the second is the operating principle of an AC motor.

Changing the direction of current relative to the magnet

In order to change current frames in a conductor, 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 current to the frame. When one ring replaces two, when the frame is rotated half a turn, the direction of the current changes to the opposite, but the torque maintains it. It is important to take into account 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, naturally, has a more complex design, using dozens of frames 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 connected to insulated rings that form a collector. The winding, commutator and core are an armature that rotates in bearings on the body of the engine 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 supply network, 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 design with mixed excitation, when two types of winding connections are used at once.

Synchronous machine

The principle of operation is the need to create a rotating magnetic field. Then you need to place conductors flowing around a constant current in this field in this field. The operating principle of a synchronous electric motor, which has become very widespread in industry, is based on the above example with a current-carrying frame. The rotating field created by the magnet is generated by a system of windings that are connected to the power supply. Typically, three-phase windings are used, but the principle of operation of alternating current will not differ from three-phase, except perhaps by the number of phases themselves, which is not significant when considering the 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 air gap formed.

Synchronism

Very important point is the synchronous operation of the electric motor of the above design. 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. As the load increases, the machine may become out of synchronization.

Asynchronous motor

The principle of operation is the presence of a rotating magnetic field and closed frames (circuits) on the rotor - the rotating part. The magnetic field is generated in the same way as in a synchronous motor - with the help of windings located in the stator slots, which are connected to an alternating voltage network. The rotor windings consist of a dozen closed loops and frames and usually have two types of design: phase and short-circuited. The operating principle of the AC motor is the same in both versions, only the design changes. In the case of a squirrel cage rotor (also known as a squirrel cage), the winding is filled with molten aluminum into the slots. When making a 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 regulate the engine speed.

Traction machine

The operating principle of a traction motor is similar to a DC motor. From the supply network, the current is supplied to Next, three-phase alternating current is transmitted to special ones. There is a rectifier. It converts alternating current to direct current. According to the diagram, 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 one (50 Hz). Therefore, they use the operating principle of which is to convert frequencies and control this characteristic.

Through 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, which are located on the axles of the bogies. From them, current flows through the tires onto the rails and then returns to the traction substation, thus completing the electrical circuit.

An electric motor is a motor that converts electrical energy into mechanical energy.

The main part of the electric motor is a circuit (frame, coil) with current located in a strong magnetic field (Fig. 1). A torque acts on the circuit in a magnetic field, as a result of which the circuit rotates and stops in the equilibrium position, i.e. in a position in which its magnetic moment is directed parallel to the magnetic induction (the contour plane is perpendicular to the magnetic field induction lines).

If, when the circuit passes through the equilibrium position, the direction of the current changes to the opposite, then the direction of the magnetic moment will also change. Having passed the equilibrium position by inertia, the circuit will make another half turn. If you periodically change the direction of the current, the circuit will begin to rotate. Changing the direction of the current is carried out automatically using a device called a collector. The collector consists of two metal half-cylinders, to which the ends of the circuit are connected. Through them and sliding contacts (brushes), the circuit is connected to the current source.

The greatest moment acts on a circuit whose plane is parallel to the magnetic induction. Consequently, if you place two circuits perpendicular to each other and bring their ends to a quarter-ring manifold (Fig. 2), then the torque will increase sharply and the smoothness of the moving part of the engine (rotor) will increase.

In industrial motors, the magnetic field is created by the winding of an electromagnet; grooves are made in the rotor into which many turns of one section are placed (instead of a frame); the various sections are laid at an angle to each other, and their ends are brought out on opposite sides of the commutator, to which the brushes connected to the current source are pressed. From the current source, voltage is supplied to the electromagnets of the stator (the stationary part of the engine). Current flows through each section only when its plates touch the brushes, i.e. when the plane of this section is parallel to the magnetic induction vector. In this case, the sections alternately create the largest torque.

A magnet or electromagnet that creates a magnetic field is often called an inductor, and the frame (winding) through which electric current is passed is called an armature.

The main operating characteristic of an electric motor is the torque M created on the motor shaft by the Ampere force acting on the armature windings:

where I is the current strength in the winding, B is the magnetic field induction, l is the length of the conductor, r is the radius of the rotor, N is the number of turns in the winding.

Such DC motors are used in transport (in electric locomotives, trams, trolleybuses), on cranes, and in many household electrical devices (electric shavers, tape recorders, etc.).

With the help of a DC electric motor - the starter - the car engine is started.