Electric motors are power machines used to convert electrical energy into mechanical energy. The general classification divides them according to the type of supply current into DC and AC motors. The article below discusses electric motors with AC specification, their types, distinctive characteristics and advantages.

Industrial Type AC Motor

Energy conversion principle

Among electric motors used in all industries and household electrical appliances, the most common are AC motors. They are found in almost every area of ​​life - from children's toys and washing machines to cars and powerful production machines.

The operating principle of all electric motors is based on Faraday's law of electromagnetic induction and Ampere's law. The first of them describes the situation when an electromotive force is generated on a closed conductor located in a changing magnetic field. In motors, this field is created through the stator windings through which alternating current flows. Inside the stator (which is the body of the device) there is a moving element of the engine - the rotor. A current arises on it.

The rotation of the rotor is explained by Ampere's law, which states that electric charges flowing through a conductor located inside a magnetic field are acted upon by a force that moves them in a plane perpendicular to the lines of force of this field. Simply put, the conductor, which in the engine design is the rotor, begins to rotate around its axis, and it is fixed on the shaft to which the operating mechanisms of the equipment are connected.

Types of engines and their design

AC electric motors have a different design, thanks to which it is possible to create machines with the same rotor speed relative to the stator magnetic field, and machines where the rotor “lags behind” the rotating field. According to this principle, these motors are divided into corresponding types: synchronous and asynchronous.

Asynchronous

The design of an asynchronous electric motor is based on a couple of important functional parts:

1. The stator is a cylindrical block made of steel sheets with grooves for laying conductive windings, the axes of which are located at an angle of 120˚ relative to each other. The poles of the windings go to the terminal box, where they are connected in different ways, depending on the required operating parameters of the electric motor.
2. Rotor. In the design of asynchronous electric motors, two types of rotors are used:
   • Short-circuited. So called because it is made from several aluminum or copper rods short-circuited using end rings. This design, which is a current-carrying rotor winding, is called a “squirrel cage” in electromechanics.
   • Phase. On rotors of this type, a three-phase winding is installed, similar to the stator winding. Most often, the ends of its conductors go to the terminal pad, where they are connected in a star, and the free ends are connected to slip rings. The phase rotor allows you to use brushes to add an additional resistor to the winding circuit, which allows you to change the resistance to reduce inrush currents.

In addition to the described key elements of an asynchronous electric motor, its design also includes a fan for cooling the windings, a terminal box and a shaft that transmits the generated rotation to the working mechanisms of the equipment whose operation is provided by this motor.

The operation of asynchronous electric motors is based on the law of electromagnetic induction, which states that electromotive force can only arise under conditions of a difference in the speed of rotation of the rotor and the magnetic field of the stator. Thus, if these speeds were equal, the EMF could not appear, but the influence on the shaft of such “braking” factors as load and bearing friction always creates conditions sufficient for operation.

Synchronous

The design of synchronous AC electric motors is somewhat different from the design of asynchronous analogues. In these machines, the rotor rotates around its axis at a speed equal to the rotation speed of the stator's magnetic field. The rotor or armature of these devices is also equipped with windings, which are connected at one end to each other and at the other to a rotating collector. The contact pads on the commutator are mounted in such a way that at a certain point in time it is possible to supply power through the graphite brushes to only two opposite contacts.

Operating principle of synchronous electric motors:

1. When the magnetic flux in the stator winding interacts with the rotor current, a torque arises.
2. The direction of the magnetic flux changes simultaneously with the direction of the alternating current, thereby maintaining the rotation of the output shaft in one direction.
3. The desired rotation speed is adjusted by adjusting the input voltage. Most often, in high-speed equipment, such as rotary hammers and vacuum cleaners, this function is performed by a rheostat.

The most common reasons for failure of synchronous electric motors are:

• wear of the graphite brushes or weakening of the pressure spring;
• wear of shaft bearings;
• collector contamination (clean with sandpaper or alcohol).

Three Phase Alternator

History of invention

The invention of the simplest method of converting energy from electrical to mechanical belongs to Michael Faraday. In 1821, this great English scientist conducted an experiment with a conductor lowered into a vessel of mercury, at the bottom of which lay a permanent magnet. After applying electricity to the conductor, it began to move, rotating according to the magnetic field lines. Nowadays, this experiment is often carried out in physics classes, replacing mercury with brine.

Further study of the issue led to the creation by Peter Barlow in 1824 of a unipolar motor called the Barlow wheel. Its design includes two gears made of copper, located on the same axis between permanent magnets. After applying current to the wheels, as a result of its interaction with magnetic fields, the wheels begin to rotate. During the experiments, the scientist found that the direction of rotation can be changed by changing the polarity (by rearranging magnets or contacts). The practical application of the "Barlow wheel" played an important role in the study of the interaction of magnetic fields and charged conductors.

The first working prototype of the device, which became the progenitor of modern engines, was created by the Russian physicist Boris Semenovich Jacobi in 1834. The principle of using a rotating rotor in a magnetic field, demonstrated in this invention, is used almost unchanged in modern DC motors.

But the creation of the first engine with an asynchronous operating principle belongs to two scientists at once - Nikola Tesla and Galileo Ferraris, who, by a fortunate coincidence, demonstrated their inventions in the same year (1888). A few years later, the two-phase brushless AC motor created by Nikola Tesla was already used in several power plants. In 1889, Russian electrical engineer Mikhail Osipovich Dolivo-Dobrovolsky improved Tesla's invention to operate in a three-phase network, thanks to which he was able to create the first asynchronous AC motor with a power of more than 100 W. He also invented the methods used today for connecting phases in three-phase electric motors: “star” and “delta”, starting rheostats and three-phase transformers.

AC system proposed by Westinghouse

Connection to single-phase and three-phase power supplies

According to the type of supply network, AC electric motors are classified into single- and three-phase.

Connecting asynchronous single-phase motors is very easy - to do this, just connect the phase and neutral wires of a single-phase 220V network to the two outputs on the housing. Synchronous motors can also be powered from this type of network, but the connection is a little more complicated - it is necessary to connect the rotor and stator windings so that their single-pole magnetization contacts are located opposite each other.

Connecting to a three-phase network seems somewhat more complicated. First of all, you should pay attention that the terminal box contains 6 pins - a pair for each of the three windings. Secondly, this makes it possible to use one of two connection methods (“star” and “delta”). Incorrect connection can damage the motor by melting the stator windings.

The main functional difference between “star” and “triangle” is the different power consumption, which is done to enable the machine to be connected to three-phase networks with different line voltages - 380V or 660V. In the first case, the windings should be connected in a “triangle” pattern, and in the second case, in a “star” pattern. This switching rule allows in both cases to have a voltage of 380V on the windings of each phase.

On the connection panel, the winding terminals are located in such a way that the jumpers used for switching on do not cross each other. If the motor terminal box contains only three terminals, then it is designed to operate on one voltage, which is indicated in the technical documentation, and the windings are interconnected inside the device.

Advantages and disadvantages of AC electric motors

Nowadays, among all electric motors, AC devices occupy a leading position in terms of volume of use in power plants. They have a low cost, easy-to-maintain design and an efficiency of at least 90%. In addition, their device allows you to smoothly change the rotation speed without resorting to additional equipment such as gearboxes.

The main disadvantage of AC motors with an asynchronous operating principle is the fact that their shaft rotation speed can be adjusted only by changing the input current frequency. This does not allow a constant rotation speed to be achieved and also reduces power. Asynchronous electric motors are characterized by high starting currents, but low starting torque. To correct these shortcomings, a frequency drive is used, but its price contradicts one of the main advantages of these motors - low cost.

The weak point of a synchronous motor is its complex design. Graphite brushes fail quite quickly under load, and also lose tight contact with the commutator due to weakening of the pressure spring. In addition, these motors, like their asynchronous counterparts, are not protected from wear of the shaft bearings. Disadvantages also include more complex starting, the need for a direct current source and exclusively frequency control of the rotation speed.

Application

Today, electric motors with alternating current specifications are common in all areas of industry and life. They are installed as generators in power plants, used in manufacturing equipment, automotive applications, and even household appliances. Today, in every home you can find at least one device with an AC electric motor, for example, a washing machine. The reasons for such great popularity are versatility, durability and ease of maintenance.

Among asynchronous electrical machines, devices with a three-phase specification are most widespread. They are the best option for use in many power units, generators and high-power installations that require shaft speed control.

Imagine what the modern world would be like if all electric motors suddenly disappeared from it. Let's say we replaced them with heat engines. But heat engines are bulky and emit steam and exhaust gases, while electric engines of comparable power are compact, fit perfectly on machines, electric vehicles, and other equipment, while being environmentally friendly, economical and reliable. It is impossible to imagine the modern world without electric motors, which greatly facilitate people’s work, in short, making our lives more comfortable.

Thanks to electric motors, we obtain mechanical energy from electrical energy. And the decisive importance in this process is the weight and size characteristics, power and number of revolutions per minute, which in turn are associated both with the design features of the engines and with the parameters of the supply voltage.

Depending on the type of supply voltage, electric motors can be either AC or DC. By control method: stepper, linear, servo (follower). AC motors, in turn, are asynchronous and synchronous. Let's look at the types of electric motors, note their features, and talk about the operating principles of each of them.

DC motors

To build electric drives with high dynamic characteristics, DC electric motors are used. They are characterized by high overload capacity and uniform rotation. DC motors are often used in electric vehicles. They are also equipped with many machines, machines, units, including household appliances.

The operation of a classic DC motor is based on the rotation of a frame with current in an external magnetic field: current is supplied to the frame through a brush-collector assembly, and the magnetic field of the stator is obtained either from permanent magnets or from the same direct current (magnetic field of a coil with current) . As a result, the current-carrying frame rotates in a magnetic field. Instead of a frame, there may be a coil with current on a magnetic circuit - a rotor.

AC motors

AC electric motors are very widely used in everyday life and in industry, since they are considered more universal compared to DC motors. AC motors have a simple design, are more reliable than DC motors, and are easy to handle.

For example, most home fans and industrial hoods are equipped with AC asynchronous motors. They are also equipped with winches, pumps, and machine tools. The simplicity of industrial-frequency AC motors lies in the absence of a brush-commutator assembly and complex electronics.

Stepper motors

Stepper motors operate by converting discrete DC electrical impulses into mechanical movements (steps). Office equipment, machine tools, robots - wherever high speed and uniform movement of the working body is required, stepper motors are used today. To control the rotor rotation speed, the electronic unit regulates the pulse repetition rate and their duty cycle. A stepper motor is a synchronous brushless DC motor.

Servo drives (servo motors)

Servo drive (follower drive) is a high-tech DC motor. Unlike a stepper motor, a servomotor also has a rotor position sensor in its design, with the help of which a negative feedback mechanism is implemented.

Motors of this type are capable of developing high speeds and power, like DC stepper motors, but the adjustment of the position of the working element is more accurate. For CNC machines, a servo drive is just what you need. Many modern industrial machines are equipped with servo drives integrated into a high-precision computer control system.

Linear motors

Instead of a rotor, a linear DC motor has a rod (rod) with magnets that moves linearly through the stator relative to the inductor. Motors of this type are gaining popularity as drives for mechanisms with reciprocating movements during operation.

This is a reliable and economical solution, eliminating the need to use any mechanical transmission. Pulses of the required polarity and duration are sent to the coil, forming a magnetic field of the desired configuration, which in turn acts on the rod, and the current position of the rod is monitored thanks to Hall sensors built into the stator.

Synchronous electric motors

When speaking of a “synchronous motor,” they traditionally mean an alternating current motor in which the rotational speed (or angular velocity) of the rotor is equal to the angular velocity of the magnetic flux in the stator cavity. Most often we are talking about motors whose rotors carry permanent magnets or an excitation winding, which creates a strong own magnetic field that prevents slipping.

With synchronous motors, the rotor speed is therefore constant. Powerful fans, crane drives, pumps - in many applications where high power and constant speed are required, regardless of the load, synchronous motors are used.

Asynchronous electric motors

Most often, an asynchronous motor is an alternating current motor in which the frequency (or angular speed) of rotor rotation differs from the angular speed of the stator magnetic flux. That is, there is “slip” in such an engine. AC induction motors come with a squirrel-cage rotor or .

More powerful asynchronous motors are made with a wound rotor; the magnitude of the magnetic flux of such a rotor is controlled by a rheostat, and the rotation speed is adjustable. Less critical (to the dependence of the rotor speed on the load) equipment is equipped with asynchronous motors with a squirrel-cage rotor.

In household appliances, hand-held power tools, automotive electrical equipment and automation systems, a commutator AC motor is often used, the connection diagram of which, as well as the device, are similar to DC motors.

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Their widespread use is explained by their compactness, low weight, low cost and ease of operation. In this segment, motors with high frequency and low power are most in demand.

This device is quite specific, having, due to its similarity with DC machines, similar characteristics and inherent advantages.

The difference from DC motors is the material of the stator housing, made of sheets of electrical steel, due to which it is possible to reduce eddy current losses.

So that the engine can operate from a regular network, i.e. 220 V, field windings are connected in series.

These motors, called universal due to the fact that they operate on alternating and direct current, are single- and three-phase.

Video: Universal brushed motor

What does the structure consist of?

The design of an AC electric motor includes, in addition to the rotor and stator:

• tachogenerator;
• brush-collector mechanism.

The armature current interacts with the magnetic flux of the field winding, causing rotor rotation in the collector mechanism. Current is supplied through the brushes to the commutator, which is the rotor assembly and is connected in series to the stator winding. It is assembled from plates with a trapezoidal cross-section.

The principle of operation of such an engine can be demonstrated using the well-known experiment from school with a rotating frame, which was placed between opposite poles of a magnetic field. It rotates under the influence of dynamic forces when current flows through it. When changing the direction of the current, the frame does not change the direction of rotation.

High idle speeds caused by the maximum torque when connecting the field windings in series can lead to failure of the mechanism.

Connection diagram (simplified)

A typical connection diagram provides for the output of up to ten contacts to the contact strip. The current L flowing through one of the brushes enters the commutator and armature, then passes to the stator windings through the second brush and jumper, leaving the neutral N.

This method of connection does not provide for reversing the motor, since connecting the windings in parallel leads to a simultaneous change in the poles of the magnetic fields. As a result, the direction of the moment is always the same.

It is possible to change the direction of rotation if you change the locations of the winding outputs on the contact strip. The motor is turned on directly when the rotor and stator outputs are connected to a brush-commutator mechanism. To turn on the second speed, the terminals of half the winding are used. We must not forget that from the moment of such connection the motor operates at maximum power, so its operation time cannot exceed 15 seconds.

Video: Connecting and adjusting engine speed from a washing machine

In practice, various methods of regulating engine operation are used. This can be an electronic circuit where the regulating element is a triac, which “passes” a given voltage to the motor. It works like an instantaneous key, opening when a control impulse is received at its gate.

The principle of operation implemented in circuits with a triac is based on full-wave phase control, where the voltage supplied to the motor is tied to the pulses that arrive at the electrode. In this case, the frequency with which the armature rotates is directly proportional to the voltage supplied to the windings.

Simplified, this principle can be described by the following points:

• a signal from an electronic circuit is supplied to the triac gate;
• the gate opens, current flows through the stator windings, causing the motor armature M to rotate;
• instantaneous rotation speed values ​​are converted by the tachogenerator into electrical signals, forming feedback with control pulses;
• as a result, the rotation of the rotor remains uniform under any load;
• Using relays R and R1, the motor is reversed.

Another circuit is a phase-pulse thyristoran.

Machine advantages and disadvantages

The advantages include:

• small sizes;
• versatility, i.e. work on constant and alternating voltage;
• high starting torque;
• independence from network frequency;
• speed;
• soft adjustment of rotation speed over a wide range when varying the supply voltage.

Disadvantages are also associated with the use of a brush-collector junction, which entails:

• reducing the service life of the mechanism;
• sparks occurring between the brushes and the commutator;
• high noise level;
• a large number of collector elements.

Basic faults

The sparking that occurs between the brushes and the commutator is the most important issue that requires attention. To avoid more serious malfunctions, such as peeling and deformation of the lamellas or overheating of the lamellas, a worn-out brush must be replaced.

In addition, a short circuit between the armature and stator windings is possible, causing strong sparking at the commutator-brush junction or a significant drop in the magnetic field.

To extend the service life of the engine, two conditions must be met - a professional manufacturer and a competent user, i.e. strict adherence to operating hours.

Video: Brushed electric motor

The electric motor is a special converter. This is a machine where electrical energy is converted and converted into mechanical energy. The operating principle of the engine is based on electromagnetic induction. There are also electrostatic motors. Without any special additions, it is possible to use engines based on other principles of converting electricity in motion. But few people know how an electric motor works and how it works.

How the device works

An AC electric motor contains fixed and moving parts. The first include:

• stator;
• inductor.

Stator finds application in machines synchronous and asynchronous type. The inductor is used in DC machines. The moving part consists of a rotor and an armature. The first is used for synchronous and asynchronous devices, while the armature is used for equipment with constant performance. The function of the inductor lies on low-power motors. Permanent magnets are often used here.

When talking about how an electric motor works, it is necessary to determine what class of equipment a particular model belongs to. In the design of an asynchronous motor, the rotor is:

• short-circuited;
• phase, that is, with a winding.

The latter type is used if it is necessary to reduce the starting current and adjust rotation speed asynchronous electric motor. Usually we are talking about crane electric motors, which are widely used in crane installations.

The crane has mobility and is used in DC machines. This can be a generator or engine, as well as a universal engine, operating on the same principle. It is used in power tools. In fact, a universal motor is the same motor with constant performance, in which sequential excitation occurs. The only difference concerns winding calculations. There is no reactance here. It happens:

• capacitive;
• inductive.

That is why any power tool, if the electronic unit is removed from it, can operate on direct current. But at the same time, the voltage in the network will be less. The operating principle of an electric motor is determined according to what components it consists of and for what purposes it is intended.

Operation of a three-phase asynchronous motor

When connected to the network, a rotating magnetic field is formed. It is noted in the stator and penetrates through the short-circuited rotor winding. It goes into induction. After this, in accordance with Ampere's law, the rotor begins to rotate. The frequency of movement of this element depends on the frequency of the supply voltage and the number of magnetic poles represented in pairs.

The difference between the rotor speed and the stator magnetic field is expressed as slip. Engine called asynchronous, because the frequency of rotation of its magnetic field is consistent with the frequency of rotation of the rotor. A synchronous motor has differences in design. The rotor is complemented by a permanent magnet or an electromagnet. It contains elements such as a squirrel cage for launching and permanent magnets. Electromagnets can also play their role.

In an asynchronous motor, the rotation speed of the stator magnetic field coincides with that of the rotor. To switch on, auxiliary-type asynchronous electric motors or a rotor with a squirrel-cage winding are used. Asynchronous motors have been able to find wide application in all technical fields.

This is especially true for three-phase motors, characterized by simplicity of design. They are not only affordable, but also more reliable than electric ones. They require almost no care. The name asynchronous given to them is due to the non-synchronous rotation of the rotor in such an engine. If there is no three-phase network, such a motor can be connected to a single-phase current network.

The stator of an asynchronous electric motor contains a package. It contains varnished electrical steel sheets whose thickness is 0.5 mm. They have grooves where the winding is laid. The three phases of the winding are connected to each other by a triangle or star, which are offset by 120 degrees spatially.

If we are talking about the rotor of an electric motor, in which there are slip rings in the grooves, a situation similar to the stator winding is noted. This is true if it is connected by a star or the initial ends of the phases are connected by three slip rings fixed on the shaft. When the engine is running, you can connect a rheostat to the winding phases to control the rotation speed. After a successful run-up, the slip rings are short-circuited, and therefore the rotor winding performs the same functions as in the case of a short-circuited product.

Modern classification

Based on the principle of torque generation, electric motors are divided into magnetoelectric and hysteresis. The last group differs in that the torque here is formed due to hysteresis when the rotor is excessively magnetized. Such engines are not considered classic and are not so common in industry. The most widespread are magnetoelectric modifications, which are divided into two large groups, according to the energy consumed. These are AC and DC motors. Universal models are also available that can be powered by both types of electric current.

Key Features

It would be correct to call these devices non-phase electrical. This is because the phases switch here directly in the engine. Due to this, the motor is powered by direct as well as alternating types of current, with equal success. This group is divided according to the method of phase switching and the presence of feedback. They come in valve and manifold types.

Regarding the type of excitation, commutator motors are divided into models with self-excitation, motors with independent excitation from permanent magnets and electromagnets. The first type, in turn, is classified into motors with serial, parallel, and mixed excitation.

Brushless, or valve-operated, products operate on electricity. In them, phase switching occurs through a special electrical unit called an inverter. This process can be equipped with feedback when the rotor position sensor is activated or without feedback. Such a device can actually be positioned as an analogue of an asynchronous device.

Pulsating current units

Such a motor is electric and is powered by a pulsating electric current. Its design features are similar to those of DC devices. Its design differences from a motor with constant performance consist in the presence of laminated inserts for rectifying alternating current. It is used on electric locomotives with special installations. A characteristic feature is the presence of a compensation winding and a significant number of pole pairs.

AC Modifications

A motor is a device powered by alternating current. These units are asynchronous and synchronous. The difference is that in asynchronous machines the magnetomotive force of the stator moves with the speed of rotation of the rotor. With asynchronous equipment, there is always a difference between the rotation speed of the magnetic field and the rotor.

A synchronous electric motor operates on alternating current. The rotor here rotates in accordance with the movement of the magnetic field of the supply voltage. Synchronous electric motors are divided into modifications with field windings, with permanent magnets, as well as reactive modifications, hysteresis, stepper, hybrid reactive types of devices.

There is also a so-called reactive-hysteresis type. Models with stepper units are also produced. Here, a certain position of the rotor is fixed by supplying power to certain areas of the winding. The transition to another position is achieved by removing the voltage from some windings and moving it to other areas. Electrical type valve reluctance models form power supply of windings via semiconductor elements. An asynchronous device has a rotor speed that is different from the frequency of the rotating magnetic field. It is created by the supply voltage. Such models are most widespread today.

Universal collector equipment

Such a unit can operate on alternating and direct current. It is made with a series excitation winding with power ratings of up to 200 W. The stator is made of special electrical steel. The excitation winding is carried out completely at a constant voltage and partially at a variable voltage. The rated voltage for alternating current is 127 and 220 V, the same indicators for the constant parameter are 110 and 220 V. They are used in power tools and household appliances.

How an electric motor works depends on whether it belongs to a particular type of equipment. AC modifications powered from a 50 Hz industrial network do not allow the rotation speed to exceed 3000 rpm. That is why, to obtain significant frequencies, an electric-type commutator motor is used. It is also lighter and smaller in size than variable-rate devices with similar power.

In their regard, special transmission mechanisms are used that transform the kinematic parameters of the mechanism to acceptable ones. When using frequency converters and in the presence of a high-frequency network, AC motors are lighter and have smaller commutator components.

The service life of asynchronous models with variable indicators is significantly higher than that of collector models. It is determined by the condition of the bearings and the characteristics of the winding insulation.

A synchronous motor, which has a rotor position sensor and an inverter, is considered the electronic equivalent of a brushed DC motor. In fact, it is a commutator electric motor with stator windings connected in series. They are ideally optimized for use with household electricity. Such a model, regardless of the voltage polarity, can be rotated in one direction, since the series connection of the windings and rotor guarantees a change in poles from the magnetic fields. Accordingly, the result remains directed in one direction.

A stator made of magnetic soft material is suitable for operation on alternating current. This is possible if its magnetization reversal resistance is insignificant. To reduce eddy current losses, the stator is made of insulated laminations. It turns out typesetting. Its peculiarity is that the current consumption is limited due to the inductive reactance of the windings. Accordingly, the motor torque is estimated to become maximum and varies from 3 to 5. To bring general-purpose motors closer to the mechanical characteristics, sectional windings are used. They have separate conclusions.

It is noteworthy that some types of bacteria use an electric motor made of several protein molecules to move. It is capable of transforming the energy of electric current in the form of the movement of protons in the rotation of the flagellum.

The synchronous reciprocating motion model works in such a way that the moving part of the device is equipped with permanent magnets. They are fixed on the curtain. By means of stationary elements, permanent magnets are exposed to a magnetic field and move the rod in a reciprocating manner.

Electric motors are versatile units capable of converting electricity into mechanical energy. Today there are various types and classifications of electric motors used in domestic and industrial installations. Such equipment may differ in its operating principle, power supply from direct or alternating current, power and purpose.

Operating principle and design features

The design of the electric motor is standard, which greatly simplifies the operation and repair of equipment. The stator and rotor, which are the main elements of the technology, are located inside a cylindrical groove. When voltage is applied to the stationary stator winding, a magnetic field is excited, which drives the rotor and shaft of the electric motor.

Constant movement of the rotor is maintained by re-commutation of the windings or by creating a rotating magnetic field in the stator. If the first method of supporting shaft rotation is typical for collector modifications of units, then the formation of a rotating magnetic field is inherent in three-phase asynchronous motors.

The electric motor housing can be made of aluminum alloy or cast iron. In each specific case, the choice of body material is made based on the scope of use of the equipment and its required weight parameters.

All motors are manufactured with the same installation dimensions, which significantly simplifies their installation and subsequent operation.

Scope of use

The purpose of the electric motor is extremely wide. Such units are used to amplify the power of electrical signals; they are capable of converting direct current into alternating current and can be used in various types of electric machines. It is customary to distinguish between units intended for use in industrial equipment, mechanical engineering, on various lifting machines and special equipment. Also very popular are low-power electric motors, which are successfully used in various household tools and kitchen appliances.

Equipment classification

Today, there are various classifications of electric motors, which differ in different criteria and characteristics. Depending on the characteristics of the technology, it is customary to classify it:

In the hysteresis type modification, the rotation of the shaft is based on the magnetization reversal of the rotor. Such engines were popular in the past, but today their design is outdated, so they are practically not found. The most widespread are magnetoelectric units that can operate on alternating or direct current, as well as universal-type models that are simultaneously powered by alternating and direct current.

Magnetoelectric installations

The use of magnetoelectric modifications of DC motors allows one to obtain excellent dynamic and operational characteristics. Depending on its design, such The type of engines is divided into two main categories:

• with permanent magnets;
• with electromagnets.

In recent years, modifications with electromagnets, which have greater power, are more economical in operation and allow you to quickly change equipment operating parameters, have become the most popular.

In commutator motors, a brush assembly is used to connect the rotating and stationary parts of the motor. Such units can be made with independent excitation and the use of permanent magnets, but there are also those that are of a self-exciting type with a mixed, series or parallel connection. Manifold modifications have mediocre reliability indicators. They require competent and timely maintenance.

Brushless valve units have a closed system that operates on the principle of synchronous devices. High-quality brushless electric motors are equipped with a sensor for reading the rotor position and have a coordinate converter, based on the data from which the device operates.

Valve motor types can have different sizes and power. Such units are used in industrial equipment. They are also equipped with cordless tools, various toys and mobile phones.

Synchronous AC motors include modifications in which the rotor rotates synchronously with the generated magnetic field. A special feature of such units is their high power, which can reach hundreds of kilowatts. The main areas of use for synchronous equipment are powerful industrial plants, wind generators and hydroelectric power plants.

It is customary to distinguish several modifications of synchronous electric motors:

• stepper;
• reactive;
• with permanent magnets;
• reactive hysteresis;
• valve reactive;
• with excitation windings;
• hybrid synchronous.

For stepper synchronous motors with discrete angular motion of the shaft, the rotor position will be fixed by applying voltage to the circuit windings. The transition to another shaft position is carried out by removing power from some windings and then applying voltage to other windings of the transformer.

Also widely used is a switched reluctance motor, the winding of which is made of semiconductor elements. Switched reluctance units are characterized by increased power, and they can be fully electronically controlled, which allows both maintaining minimum speed and quickly reaching full power at maximum speed. The advantages of synchronous motors include:

• stable rotation speed;
• low sensitivity to voltage changes in the network;
• possibility of use as a power generator;
• minimal power consumption.

However, synchronous devices still have disadvantages. These include difficulties with starting, difficulties with maintenance, and problems with adjusting the shaft speed. The main purpose of such devices is powerful industrial equipment, where the performance of units and their reliability are valued.

Asynchronous modifications

For asynchronous AC motors, the rotor speed will differ from the magnetic field. Such units are also called induction, which is explained by the principle of generating a magnetic field that arises due to the movement of the stator. Asynchronous modifications are most widespread, which is explained by the simplicity of their design, reliability, durability, as well as the ability to implement both heavy-duty industrial installations and small electric motors intended for use in household tools.

Depending on the type of electric current with which such units operate, They are usually divided into three categories:

• single-phase;
• two-phase;
• three-phase.

The most widespread today are single-phase asynchronous motors that can operate from a household electrical network. A feature of single-phase motors is the presence of only one working winding and a squirrel-cage rotor on the stator. An alternating single-phase current is supplied to the stator winding, driving the rotor and motor shaft. The rotor itself has a cylindrical core with aluminum-filled cells and open ventilation blades. Single-phase squirrel cage motors are used in small power devices, water pumps and room fans.

Two-phase asynchronous motors are designed for use in single-phase AC power. Their feature is the presence of two working windings on the stator, located perpendicular to each other. During operation of the unit, alternating current is directly supplied to one winding, and to the second through a corresponding phase-shifting capacitor. A rotating magnetic field is formed at the output, which simplifies the start of the electric motor and subsequently maintains consistently high speeds.

Three-phase motors can have a squirrel cage and a wound rotor. The units are equipped with three working windings located on the stator parallel to each other. When the motor is connected to a three-phase network, the magnetic field has a spatial shift relative to the winding by 120 degrees. The presence of a short-circuited field makes it easier to put the device into operation, while subsequently maintaining stable speeds. Modifications of wound rotor motors are characterized by increased power and are used primarily in industrial equipment.

The advantages of asynchronous electric motors are their resistance to voltage surges and versatility of use. Due to the simplicity of the design, their subsequent maintenance is greatly simplified, and the equipment itself is extremely reliable and does not cause any trouble during operation. Depending on their modification, the installations can operate both from a powerful source of electricity in a three-phase network, and from a household electrical network, which allows them to be used in various household appliances and all kinds of electrical appliances.

Electric motors are the simplest and extremely reliable devices that are widely used in industry and everyday life. The currently existing types of electric motors make it possible to select a unit that will fully comply with the characteristics of its operation. With the help of such motors, powerful machines and equipment and efficient pumps can be driven. Not a single household electrical appliance can do without their use.