The difference between a synchronous machine and an asynchronous machine. How are asynchronous motors different from synchronous motors?

22.04.2019

The transfer of electric motors from the collector control unit to semiconductor control devices made it possible to optimize power units. Modernization affected both power parameters and design characteristics. The most pronounced difference was the reduction in dimensions, which made it possible to use such units in small-sized devices and installations. A typical example The implementation of a brushless drive is a brushless motor operating in direct current conditions. It provides significant technical and economic advantages during operation, but is not free from disadvantages.

The design and arrangement of the engine

The technical infrastructure is formed by two segments - directly by the mechanics and the control complex. From the point of view of the structural device, the unit is in many ways similar to the traditional filling of electromechanical rotary engines. Accordingly, the composition of the electric motor includes a rotor, a stator and a winding. Moreover, the stator is a set of separate insulated sheets made of steel alloy. During operation, they contribute to the reduction of eddy currents. It just contains the winding, which can have a different number of phases. The filling of the element is formed by a steel core, and the winding is made of copper fibers. For protection, a housing is used, on the surface of which means of physical fastening are also provided.

As for the rotor, it is formed by permanent magnets. Depending on the modification, it can have up to sixteen pairs of alternating poles. Previously, ferrite magnets were used for the manufacture of rotors, which was due to their affordability. Today comes to the fore performance characteristics brushless motor - in particular the torque, which varies from 1 to 70 Nm. The throughput frequency is on average in the range of 2-4 thousand revolutions. To achieve such indicators, a magnet with a high degree of induction is required, so manufacturers have switched to the use of rare earth alloys. Such magnets not only give higher performance, but also have smaller dimensions. In part, this transition also contributed to the optimization of the dimensions of the brushless electric motor. Separately, it is worth considering the components of the control segment.

Control system

If the electromechanical part consists mainly of three components, including a rotor, a stator and a supporting structure in the form of a housing, then the control infrastructure is more segmented - the number of elements can reach several tens. Another thing is that they can be divided into types. Only the inverter will be presented in the singular. He is responsible for the switching functions, connecting and switching phases. The main tasks of control with the supply of signals are performed by sensors. The main one is the rotor position detector. In addition, a signal regulation system is also introduced into the control unit. This is a node with keys, through which the connection of sensors and electromechanical filling is realized.

Information about the position of the rotor is processed by the microprocessor. Externally, the interface of this block is a control panel. At reception, it works with pulse-width modulation (PWM) signals. If low-voltage signals are provided, then a transistor bridge is also installed in the control unit. It converts the signal into power voltage, which is then fed to the electric motor. The presence of sensors with a pulse processing system just distinguishes the control of a brushless motor from the means of controlling brush-collector units. Another thing is that the possibility of introducing electronic equipment with sensors is also allowed in collector machines along with mechanical systems management.

Principle of operation

The valve electric motor during operation creates an induction of magnetic poles through the rotor. Against the background of the generation of electromagnetic influence, resistance is formed. In other words, the rotor function is activated, after which it transmits torque to the target unit. Under variable speed conditions, the magnetism can be optimized for better reverse performance. Again, the rotor position sensor reports data for regulation according to voltage phases. Flexibility and speed of setting the parameters of the rotor and the number of phases allows you to more effectively regulate the operation of the mechanism. The whole cycle demonstrates the process of converting electricity into physical power (mechanical energy) that is generated by the generator. Moreover, if the unit is sharply disconnected from the network, then converted into this moment energy will be returned to the stator.

An important condition for maintaining sufficient performance is the stability of the engine. The criterion for evaluating this characteristic will be its smoothness, achieved by lowering the pulsations. To do this, you need to know the rotation vector of the stator flux so that it is synchronous with the function of the rotor. The coordination of different rotation flows is precisely achieved by the interaction of sensors and the commutator, which controls the valve motors. The principle of operation of this bundle allows you to determine with high accuracy which phase the rotor should be connected to, also determining the axis. In the required sequence, the control panel through the microprocessor alternately connects and disconnects different phases.

Features of synchronous models

The above principle of operation just illustrates the operation of a synchronous motor. That is, it implements the interaction of the poles of the inductor and the stator magnetic field. But even in such systems there may be differences. For example, both synchronous and asynchronous motors can be equipped with electromagnets. In the case of synchronous units of this type, the current will be directed to the rotor, bypassing the brush-ring contact. Permanent magnets are used in drives based on hard drives. There are also inverted structures. In them, anchor flows are on the rotor, and induction is on the stator.

To turn on a synchronous motor, a high frequency acceleration is required in order to be able to adjust the rotation of the two functional components. In designs where the inductor is located on the stator, the rotor field remains stationary relative to the armature. Conversely, if the device assumes a reverse design, then the “timing input” will be carried out by waiting for the stator. The waiting time depends on the load with which the brushless motor operates and what frequency is optimal for activating its inductor.

Features of asynchronous aggregates

In asynchronous motors, the rotor does not rotate in the opposite direction. It cannot be called the reverse of a synchronous unit in terms of the interaction of the magnetic fluxes of the rotor and stator. Both a synchronous and an asynchronous motor assume the following of one field after another. Another thing is that in the second case, the rotor, for example, can be "catching up". It follows the generation of the induction moment.

In a standard design, the stator generates an electromagnetic field, causing the rotor to rotate after a certain time. The fundamental difference between the two types of motors is that the inductor is not a generator of excitation of the magnetic field of the rotor. Therefore, an asynchronous type permanent magnet motor can autonomously make the rotor rotate at a certain frequency from the stator winding. This does not mean that the two mechanisms work separately, but their functions are not as closely interconnected as in the case of synchronous motors. The same applies to speed. For example, if in a synchronous assembly there will be a rotation speed of 3000 rpm for the inductor and rotor, then asynchronous principle work for the same rotor can reduce this value to 2910 rpm.

Switched reluctance motor

We can say that all valve motors are inductor. In varying degrees, the principle of induction is laid in synchronous and asynchronous units. But there are also models in which induction promotes self-magnetization. Otherwise, this machine can be called self-excited. In the traditional version, this type of switched reluctance motor has simple design, is powered by unipolar current pulses and works with the same rotor sensors. However, due to the nuances of the power supply, it cannot be connected directly to the network. As a result, the introduction of special converters into the infrastructure is required.

On the other hand, this design contains almost all the advantages of synchronous units. The most obvious of these is the wide range of rotational speeds. For example, a valve-reluctance engine with the possibility of self-excitation is capable of delivering about 100 thousand revolutions. These are already high-speed electric motors, for which components of a high degree of strength are used.

Varieties of units by the number of phases

The simplest version of such an electric motor is single-phase units, which provide for a minimum number of contacts between electronic equipment and mechanics. Accordingly, it follows from this weak spots designs, including restrictions in the position of the rotor and strong pulsations. Two-phase models are able to form an air gap, and also, under certain conditions, provide asymmetry of the poles. Again, such machines suffer from a high degree of ripple, but they can be used in cases where the connection of the stator with the winding is a prerequisite. The three-phase brushless motor is characterized by a combination of low speed, but good power output. Therefore, it is more often used both in the assembly of household appliances and in the manufacture of industrial equipment. There are also four- and six-phase models of valve electric motors, but these are already segments of specialized installations that are expensive and have large dimensions.

Advantages of electric motors

Valve-assisted power technology offers many operational advantages through design optimization. Among them, it is worth noting the speed, flexibility in setting, the accuracy of determining the position of the rotor (using a sensor), the wide possibilities of technical adjustment, etc. With modest energy costs, you can get a high power output. More importantly, the brushless motor uses a small resource mechanical action, and this has a positive effect on its service life. Low level thermal impact on the element base causes the absence of overheating, therefore, parts only in rare cases require replacement due to wear.

Disadvantages of the electric motor

Experts note two main disadvantages of such electric motors. First of all, this is the complexity of the design. Not a mechanical part, but an electronic basis that provides motor control. The use of microprocessors, sensors, inverters and related electrical fittings requires an appropriate approach to ensure the reliability of the system components. Thus, the cost of maintenance of equipment also increases. At the same time, the high cost of magnets, on which the brushless motor is based, even in simple single-phase versions, is also noted. In practice, users try to replace expensive items and consumables, at the same time simplifying the control system. But such measures in themselves require certain resources, not to mention the fact that the efficiency of the engine is reduced.

Conclusion

The concept of using electronics in traditional rotary engines is not always justified during operation. This is due to the scope of such equipment. Most often these are traditional areas of production, where connection is not necessary at all. electronic systems management. Innovative stuffing forces us to revise production cycles, pointwise upgrading technological processes. In addition, the cost of the engine, which varies from 15 to 20 thousand rubles, does not add to the attractiveness of this product. Conventional analogues on controllers with electromechanical relays are cheaper, not to mention the fact that they are easier to integrate into the product assembly process.

And yet there are areas in which the semiconductor control with rotor sensors is highly valued. As a rule, this is high-tech equipment, which is produced by large companies. And at the end they provide products different levels, including for home use.

Details Posted on 08.11.2018 12:14

The history of electric motors is over 170 years, but most of their development can be seen in the last ten or so years. Appearanceelectronic control systems that allow speed and torque control, and therefore various types of frequency converters andsystems soft start have revolutionized the market for the use of such electric actuators.

Nowadays, electric motors are used not only to control various types machines, but also in modern automation systems.A motor interacting with a frequency converter or servo drives is used in conveyors, positioning systems, as well as inapplications, including multi-axis applications that require precise, fast and synchronized movements.

DRIVE TECHNOLOGY IN AUTOMATION

The drive technology used in widely understood automation systems covers quite a few large group devices.

There are not only engines direct current, synchronous motors alternating current, asynchronous motors, frequency converters, but alsoservo drives, gearmotors and other mechanical elements that allow you to adjust the speed and torque of the engine.

The most commonly used in automation are motors and low-voltage drives with power from 1 kilowatt to no more than a few.tens and sometimes hundreds. Engines with energy recovery systems are becoming more and more popular in the world. This is connected not only withthe need for high-performance devices, but also with consumption and energy regulations that are becoming increasinglytough in many countries.

Small AC motors offered by Ukrainian suppliers are both synchronous and asynchronous motors. Universalmotors that can operate with both constant and variable DC power are much less popular amongUkrainian consumers. As already mentioned, the most sold are motors with power from 1 W to 5 kW, as well as devices with power from 5 W to 10 kW.

It should be noted that in Ukraine the most popular now are asynchronous motors, which can be easily used in all types ofdrive systems where precise motor control is not required. Asynchronous electric motors buy Ukraine from world leaders SIEMENS, ABB, FESTO, Phoenix Contact you can on the website /simat.com.ua/

In the case of servo drives, users pay attention to the dynamics of the drive and the accuracy of the movement. Parameters such as efficiency are also important.engine, which significantly affects the total cost of maintaining an automation system in a given company.

Modern electric motors are characterized by simple configuration and ease of operation. Engineers are focusing on improving their efficiency andimprovement of operating parameters, as well as their automatic adaptation to changing load conditions.

Pro-environmental engine construction and low energy consumption are also becoming more and more important. Electric motors systematicallyundergo miniaturization. Unfortunately, after reducing the size of the engines, there is no reduction in power, but their carrying capacity increases.
Taking into account the control, there is a trend towards the digitalization of electric motors. There are more and more protocols and communicationtechnologies that are based primarily on Industrial Ethernet.

Induction motors are used to drive drives, but they have specific applications.

Induction motors are used in applications with less technological gearing, but where the moment of inertia of the drive is significant. Suchapplications are flat roller conveyors or, pumps, fans, elevators, says Konrad Florczyk, software engineer SEW-EURODRIVE Polska.

Synchronous servo motors are mainly for special applications. low moment inertia - high dynamics plus efficient and effective control -these parameters make it possible to use these motors as manipulators or final mechanisms of machines.

ASYNCHRONOUS MOTORS

Induction motors are the most commonly used types of electric motors in industry and automation. It is estimated that more than half of the electricity produced in power plants is consumed by induction motors. Their advantages include, above all, simplicity of design, ease of operation and low purchase and maintenance costs. Asynchronous motors have good options movement, and their characteristics can be formed by changing the power supply and resistance of the windings of the machine, which is achieved by connecting the appropriate external elements. Electronic, semiconductor control systems allow smooth starting and braking of asynchronous motors.

It is also easy to adjust the power and speed of this type of motor. Unfortunately, induction motors also have disadvantages. The biggest of these is the need to provide inductive reactive power, which affects the increase in power losses in power lines and noticeable voltage drops, especially visible during start-up.

Induction motors, in terms of power supply, can be divided into single-phase, two-phase and three-phase, the latter being the most popular in the industry. IN small engines two- or single-phase power supply is used.

SYNCHRONOUS MOTORS

The main task of an electric motor is to convert electricity into mechanical energy. As with most electrical machines, the reverse is possible.the process in the engine (the so-called principle of reversibility of work), i.e., the conversion of mechanical energy into electricity. However, this propertyrarely used in industrial practice.

Today's electric motors can be divided in many different ways. The simplest division is related to the type of power supply, that is, to DC andalternating current. .

However, from the point of view of drive systems, the most important is the division of motors according to their design and principle of operation. In the case of machinesAC motors There are three main groups of motors: synchronous machines, asynchronous machines and AC machines.

The most numerous group of motors presented in industrial automation systems are synchronous and asynchronous motors withalternating current. Synchronous motors differ from asynchronous motors in the design of the rotor, which is additionally equipped withelectromagnets or permanent magnets.

A synchronous motor is an electrical machine powered by alternating current in which the rotor rotates in a steady state with the sameangular velocity as the magnetic field that activates it. It is important to note that the speed of a synchronous motor is always constant and does not depend onon load and supply voltage.

The classification of engines is based on different parameters. According to one of them, a synchronous and asynchronous motor is distinguished. Differences between devices general characteristics and the principle of operation are described in the article.

This type of engine is able to work both as a generator and as an engine at the same time. Its device is similar to a synchronous generator. characteristic feature motor is the constant rotational speed of the load.

These types of motors are widely used in many fields, such as electrical wires that need constant speed.

The principle of operation of a synchronous motor

Its functioning is based on the interaction of the rotating magnetic field of the armature and the magnetic fields of the inductor poles. Usually the armature is located in the stator, and the inductor is located in the rotor. For powerful motors electric magnets are used for the poles, and permanent ones for the weak ones.

The principle of operation of a synchronous motor includes (short-term) and asynchronous mode, which is usually used to accelerate to the required (that is, nominal) rotation speed. At this time, the inductor windings are short-circuited or by means of a rheostat. After reaching the required speed, the inductor is fed with direct current.

Advantages and disadvantages

The main disadvantages of this type of engine are:

the need to supply the winding with direct current;
launch difficulty;
sliding contact.

Most generators, wherever they are used, are synchronous. The advantages of such engines in general are:

This type of device is a mechanism aimed at transforming AC electrical energy into mechanical energy. From the very name "asynchronous" we can conclude that we are talking about a non-simultaneous process. Indeed, the frequency of rotation of the stator magnetic field here is always higher than the rotor one. Such a device consists of a cylindrical stator and a rotor, depending on the type of which squirrel-cage induction motors can also be with a phase rotor.

Operating principle

The operation of the engine is carried out on the basis of the interaction of the magnetic stator field and the currents induced by the same field in the rotor. Torque appears when there is a difference in the frequency of rotation of the fields.

Let's recap now. What explains the widespread use of one type and the limited use of the other?

Synchronous and asynchronous motor: differences

The difference between the operation of engines is in the rotor. In the synchronous type, it consists in a permanent or electric magnet. Due to the attraction of opposite poles, the rotating field of the stator also attracts the magnetic rotor. Their speed is the same. Hence the name - synchronous.

It can be achieved, in contrast to asynchronous, even voltage advance in phases. Then the device, like capacitor banks, can be used to increase power.

Asynchronous motors, in turn, are simple and reliable, but their disadvantage is the difficulty in adjusting the speed. To reverse a three-phase asynchronous motor (that is, change the direction of its rotation in the opposite direction), change the location of two phases or two linear wires approaching the stator winding.

If we consider the speed, then they also have differences between a synchronous and asynchronous motor. In the synchronous type, this indicator is constant, unlike the asynchronous one. Therefore, the first is used where a constant speed is needed and full controllability, for example, in pumps, fans and compressors.

It is very simple to identify the presence of the types of devices in question on a particular device. An asynchronous motor will have a non-round number of revolutions (for example, nine hundred and thirty per minute), while a synchronous motor will have a round number (for example, a thousand revolutions per minute).

Both those and other motors are controlled quite difficult. The synchronous type has a rigid mechanics characteristic: with any changing load on the motor shaft, the rotational speed will be the same. In this case, the load, of course, must change so that the engine is able to withstand it, otherwise this will lead to a breakdown of the mechanism.

This is how a synchronous and asynchronous motor works. The differences between both types determine the scope of their use, when one type copes with the task in an optimal way, for the other it will be problematic. At the same time, you can meet and combined mechanisms.

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Synchronous and asynchronous motor: differences, principle of operation

In an induction motor, the rotor moves "by itself". It initially has no magnetic field, no electrical voltage is applied to it. It does not even have to be made of iron - a magnetic metal. Well, come on, it’s worth connecting a three-phase voltage to the motor, and the rotor spins. Without any push. But in my own way.

Two kinds of AC motors

Induction motors - naive simplicity

The rotor either catches up with the wave, or slightly lags behind, because it simply cannot run synchronously with it. This phenomenon was called "slip", having caught up with the traveling magnetic field, the rotor with the squirrel cage loses its magnetic induction and then simply slides by inertia for some time. And when friction or load forces him to lag behind the moving field, he will again “feel” in himself the changes in the lines of force of the field overtaking him and will again acquire induction, and with it the strength to move.

That is, the rotor slips slightly: either it catches up with the magnetic field running evenly in a circle, then it “forgets why it ran” and falls slightly behind, then it “recovers” again and again strives to catch up. Gradually, these deviations stabilize - depending on the friction in the bearings and the magnitude of the load on the shaft - and the asynchronous motor begins to operate simply at a rotation speed slightly lower than the frequency of the voltage on the stator. This frequency difference is called the slip frequency.

Synchronous motors: complex in simple

In order for the rotor to be connected to the traveling wave of the magnetic field of the stator coils in a rigid way, a synchronous electric motor was invented. And the problem is easily solved. In the rotor, instead of a changing magnetic field from short-circuited currents of a squirrel cage, permanent magnets and their magnetic field should be used.

There are two options. Either this is a field from a permanent magnet fixed in the rotor, or this is a field from electromagnets installed in the rotor instead of such a magnet.

An ordinary magnet, of course, is simpler. But then for the standard functioning of such electric motors, it is necessary that all of them - and thousands of electric motors are used - have exactly the same magnets. Otherwise, the motion parameters will be different, and the magnets still tend to demagnetize.

An electromagnet installed in the rotor of the engine is easier to get to produce a field of the desired quality, but an electric current is required for its operation. Such a current, which is called the excitation current, in turn must be taken somewhere and somehow fed to the rotor.

1 - rotor, 2 - excitation collector

This is where a certain variety of designs of synchronous motors comes from. But most importantly, synchronous motors rotate their shaft strictly synchronously with the frequency of the stator coil field running in a circle, that is, their rotation speed is exactly equal to - or a multiple (if the stator windings are more than three) - the frequency of the alternating current in the supply network.

However, among other things, a synchronous motor has the property of complete reversibility. Because a synchronous motor is the same generator electric current, but working "in reverse side". In the generator, some mechanical force rotates the shaft with the rotor, and from this, an induced voltage occurs in the stator windings. electrical voltage from the rotating magnetic field of the rotor. And the difference between a synchronous motor and a generator is that the voltage in the stator coils generates a magnetic field running in a circle, which, interacting with a constant magnetic field rotor, pushes it so that the rotor also rotates.

Only if in the generator the rotation of the rotor can be mechanically given any speed, and this will change the frequency of the alternating current generated by it, then there is no such luxury in a synchronous motor. A synchronous motor rotates at the rate of change in the voltage in the network, and we maintain it strictly at 50 hertz.

Differences and disadvantages of these engines

The differences between synchronous and asynchronous motors are clear from their names. Actually, both design options have advantages. Below are the advantages that both motors differ in - synchronous and asynchronous.

An asynchronous motor differs from a synchronous motor in the following parameters:

simplicity of design and low cost;
no sliding contacts, reliable operation;
voltage is applied to the fixed stator coils;
the rotor is very simple in design;
when starting and accelerating, it gradually increases power;
the ability to reverse the direction of rotation by simply swapping two supply phases;
when the movement stops (too much mechanical load on the rotor shaft), no accident occurs, the squirrel cage may overheat.

The differences between a synchronous motor and an asynchronous motor are as follows:

stable rotation speed regardless of the load on the shaft;
low sensitivity to voltage drops in the network;
when the mechanical load is reduced, it is able to work as a generator by inertia, not taking energy, but giving it to the network;
high efficiency;
able to compensate for the reactive power of the network.

But each has its own disadvantages.

Asynchronous has the following negative traits:

difficulty adjusting the speed;
low speed;
dependence of the speed lag on the axle load;
during operation, the rotor heats up due to short-circuited currents - additional cooling is required.

Disadvantages of a synchronous motor:

more complex in design
in some designs, a collector is used to conduct the excitation current in the rotor windings, as in a DC motor;
harder to start.

Despite their differences, both electric motor have found application in technology and are used in a variety of designs and sizes.

What is the difference between a synchronous motor and an asynchronous motor

Before you figure out what their difference is, you need to find out what an electric motor is? An electric motor is an electrical machine that is powered by electricity and serves as a drive for other mechanisms.

Explanation of the principle of operation of a synchronous electric motor for "dummies"

From childhood, we remember that two magnets, if they are brought closer to each other, in one case attract, and in the other they repel. This happens, depending on the fact that with what sides of the magnets we connect them, opposite poles attract, and the same poles repel. These are permanent magnets, in which the magnetic field is constantly present. There are also variable magnets.

In a school textbook on physics there is a drawing depicting an electromagnet in the form of a horseshoe and a frame with half rings at the ends, which is located between its poles.

When the frame is located in a horizontal position in the space between the poles of the magnets, due to the fact that the magnet attracts opposite poles and repels the same, a current of the same sign is applied to the frame. An electromagnetic field appears around the frame (here is an example of a variable magnet!), the poles of the magnets attract the frame, and it turns into a vertical position. When the vertical is reached, a current of the opposite sign is applied to the frame, the electromagnetic field of the frame changes polarity, and the poles of the permanent magnet begin to repel the frame, rotating it to a horizontal position, after which the rotation cycle is repeated.

This is the principle of operation of an electric motor. Moreover, a primitive synchronous electric motor!

So, a primitive synchronous electric motor works when current is applied to the loop. In a real synchronous electric motor, the role of the frame is performed by a rotor with coils of wires, called windings, to which current is supplied (they serve as sources of an electromagnetic field). And the role of a horseshoe magnet is performed by a stator made either from a set of permanent magnets, or also from coils of wires (windings), which, when current is applied, are also sources of an electromagnetic field.

The rotor of a synchronous motor will rotate at the same frequency as the current supplied to the winding terminals changes, i.e. synchronously. Hence the name of this electric motor.

Explanation of the principle of operation of an asynchronous electric motor for "dummies"

We recall the description of the figure in the previous example. The same frame, located between the poles of a horseshoe magnet, only its ends do not have half rings, they are interconnected.

Now we begin to rotate a horseshoe magnet around the frame. We rotate it slowly and observe the behavior of the frame. Until some time, the frame remains motionless, and then, when the magnet is rotated at a certain angle, the frame begins to rotate after the magnet. The rotation of the frame is delayed compared to the speed of rotation of the magnet, i.e. it rotates out of sync with it - asynchronously. So it turns out that this is a primitive asynchronous electric motor.

In fact, the role of magnets in a real induction motor is the windings located in the stator slots, which are energized. And the role of the frame is performed by the rotor, into the grooves of which metal plates are inserted, interconnected shortly. Therefore, such a rotor is called squirrel-cage.

What is the difference between synchronous and asynchronous motors?

If you put two modern electric motors of the same type side by side, then outward signs it is difficult to distinguish them even for a specialist.

In essence, their main difference is considered in the examples of the principles of operation of these electric motors. They differ in the design of the rotors. The rotor of a synchronous motor consists of windings, and the rotor of an asynchronous motor is a set of plates.

The stators of one and the other electric motors are almost indistinguishable and are a set of windings, however, the stator of a synchronous electric motor can be recruited from permanent magnets.

The speed of a synchronous motor corresponds to the frequency of the current supplied to it, and the speed of an asynchronous motor lags behind the frequency of the current.

They also differ in areas of application. For example, synchronous electric motors are installed to drive equipment that operates at a constant rotation speed (pumps, compressors, etc.) without reducing it with increasing load. And here asynchronous electric motors reduce the speed when the load increases.

Synchronous motors are structurally more complex, and therefore more expensive than asynchronous motors.

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Difference between induction and synchronous motor

Electric motors can be divided into two main categories - synchronous and asynchronous (induction) motors. These two species are quite different from each other. The difference is already visible in the names themselves. The units can be distinguished by the number of revolutions stamped on the nameplate (if the type of motor is not indicated there), the asynchronous motor has an unrounded number (for example, 950 rpm), the synchronous motor has a rounded number (1000 rpm).

There are other important differences, in this article we will consider the most significant of them: constructive, working and price.

Differences in work and cost

Any engine consists of two elements: stationary and rotating. The stator has axial slots - grooves, on the bottom of which current-carrying copper or aluminum wires are laid. At the electric motor, a rotor with an excitation winding is attached to the shaft.

The fundamental difference between synchronous and asynchronous motors are rotors, or rather, their design.

For synchronous models at low powers, they are permanent magnets.

Alternating voltage is applied to the stator winding, the rotor is connected to a constant power source. The direct current passing through the excitation winding induces a magnetic field in the stator. Torque is generated due to the angle of retardation between the fields. The rotor has the same speed as the stator magnetic field.

Units are used in practice both as generators and as engines.

Asynchronous models are fairly inexpensive motors that are used often and everywhere. They are easier to constructively, despite the fact that the fixed parts, in principle, are similar for all motors.

An alternating electric current is passed through the stator winding, which interacts with the rotor winding. Two fields rotate at the same speed in the same direction, but cannot be equal, otherwise the induced EMF and, especially, the torque would not be created. This causes an induced current in the rotor winding, the direction of which, according to Lenz's rule, is such that it tends to oppose the cause of its production, i.e., the sliding speed.

The speed of rotation of the rotor does not coincide with the speed of the magnetic field, it is always less. Thus, the rotor tries to catch up with the speed of the rotating magnetic field and reduce the relative speed.

Main advantages and disadvantages

Asynchronous units do not require any additional power supply. Synchronous requires an additional DC source to supply voltage to the windings.
Synchronizers have a relatively low sensitivity to mains voltage fluctuations and rotational stability, regardless of the load.
Induction motors do not require slip rings, except for slip ring motors, which have slip rings for soft start or speed control. Synchronous motors have more vulnerabilities because slip rings with brushes are used. Consequently, the parts wear out faster and the contact between them weakens.
Synchronizers need auxiliary triggers, as they do not have a self-start function. For induction motors with their own starting torques, such a mechanism is not required.

Which unit is better

In conclusion, it should be noted that it is impossible to say that supposedly one motor is better than another. However, asynchronous models are more reliable in operation, they are simple in design. If the units are not overloaded, then they long term service user can be satisfied.

The advantage of the synchronous model is that a high power factor can be easily set. Therefore, the model is much more efficient, but at a price it will be correspondingly more expensive. The machines are used in systems with a required power of 100 kW or more.

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Synchronous and asynchronous motor differences

Exist different kinds electric motors, and very often the question arises, what are the differences between a synchronous and asynchronous motor. IN asynchronous winding, located in the stator, create a rotating magnetic field that interacts with the currents generated in the rotor, due to which it comes into a rotating state. Therefore, at present, the simplest and most reliable asynchronous electric motor with a squirrel-cage rotor is considered the most popular.

In its grooves there are conductive rods made of aluminum or copper, connected at their ends with rings of the same material, which produce short circuit these rods. Therefore, the rotor is called short-circuited. Eddy currents interacting with the field cause the rotor to rotate at a speed less than the rotation speed of the field itself. Thus, the whole motor was called asynchronous. This movement is called relative slip, since the speeds of the rotor and the magnetic field are not equal and the magnetic field does not intersect with the current-carrying rods of the rotor. Therefore, they do not create a rotating moment.

The fundamental difference between both types of engines is the design of the rotor. In synchronous, it is a permanent magnet of relatively low power or the same electromagnet. A rotating magnet, which creates a magnetic field in the stator, drives the magnetic rotor. The speed of movement of the stator and rotor, in this case, is the same. That's why, this engine called synchronous.

Features of a synchronous motor

A synchronous motor is characterized by the possibility of a significant phase advance of the voltage by the current. Increasing the power factor by the type of capacitor banks.

Asynchronous electric motors are simple in design and reliable in operation. The only drawback of these units is the sufficient difficulty in adjusting the frequency of their rotation. Three-phase asynchronous motors can be easily reversed, i.e. the rotation of the motor can be reversed. To do this, it is enough to change the location of two linear wires or phases that are closed to the stator winding. Unlike a synchronous motor, this is a simple and cheap motor that is used everywhere.

A synchronous and asynchronous motor also has such an important difference as a constant speed for the first under various loads. Therefore, they are used in drives of machines requiring constant speeds eg in compressors, pumps or fans as they are very easy to operate.

Classification of electric motors

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What is the difference between a synchronous motor and an asynchronous motor

An engine is a device that converts energy into mechanical type work. Only knowing the functions and specifications motor, we can correctly summarize how a synchronous motor differs from an asynchronous type of device.

The principle of operation of synchronous and asynchronous motors

The functioning of synchronous electric motors is based on the interaction of the poles of the stator and the inductor. At the starting moment, the motor accelerates to the indicators of the rotational speed of the magnetic flux. Under such conditions, the device operates in synchronous mode, and a special intersection is formed by the magnetic fields, resulting in synchronization.

Synchronous motor in section

Asynchronous motors have a rotor speed that is different from the frequency at which the magnetic field rotates, created as a result of the supply voltage. Such motors do not have automatic control of current excitation.

Asynchronous motor in section

Main differences

The presence of armature windings is one of the main differences between the two types of motors.

Despite the external similarity, asynchronous motors and synchronous type devices have several fundamental differences:

the rotor of asynchronous motors does not need current supply, and the induction of the poles depends on the magnetic field of the stator;
the rotor in a synchronous motor has an excitation winding under conditions of independent power supply;
revolutions in an asynchronous motor under load lag behind the magnitude of slip from the rotations of the magnetic field inside the stator;
revolutions in synchronous motors correspond to the frequency of "turns" of the magnetic field in the stator and are constant under different loads.

Stators in asynchronous and synchronous motors are characterized by the same device and create a rotating magnetic field.

Synchronous motors are capable of operating with the simultaneous combination of the functions of a motor and a generator.

Such devices belong to the category of modern engines with high efficiency and constant speed. Asynchronous motors are more difficult to regulate, and their ratio useful action not high enough. However, the second option is more affordable.

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principles of operation and differences in characteristics

Electric motors are machines that convert electrical energy into mechanical energy. The converted energy drives the motor rotor, which transmits rotation through the transmission directly to the shaft executive mechanism. The main types of electric motors are synchronous and asynchronous motors. The differences between them determine the possibilities of using in various devices and technological processes.

Work principles

All electric motors have a fixed stator and a rotating rotor. The difference between asynchronous and synchronous motors lies in the principles of creating poles. In an asynchronous electric motor, they are created by the phenomenon of induction. All other electric motors use permanent magnets or current-carrying coils to create a magnetic field.

Features of synchronous motors

The leading units of a synchronous machine are an armature and an inductor. The armature is the stator, and the inductor is located on the rotor. Under the influence of alternating current, a rotating magnetic field is formed in the armature. It couples with the magnetic field of the inductor, formed by the poles of permanent magnets or coils with direct current. As a result of this interaction, the energy of electricity is converted into kinetic energy of rotation.

The rotor of a synchronous machine has the same speed as that of the stator field. Advantages of synchronous motors:

Structurally, it is used both as an engine and as a generator.
Load-independent speed.
Great efficiency.
Low labor intensity in repair and maintenance.
High degree reliability.

Synchronous machines are widely used as high power motors for low speed and constant load. Generators are used where an independent power source is required.

The synchronous machine also has disadvantages:

Requires a DC source to power the inductor.
There is no initial starting torque; starting requires external torque or asynchronous start.
Brushes and collectors quickly fail.

Modern synchronous units contain in the inductor, in addition to the winding supplied with direct current, also a starting short-circuited winding, which is designed to start in asynchronous mode.

Distinctive features of asynchronous motors

The rotating magnetic field of the stator of an induction motor induces induction currents in the rotor, which form their own magnetic field. The interaction of the fields causes the rotor to rotate. In this case, the rotor speed lags behind the magnetic field speed. It is this property that is reflected in the name of the engine.

Asynchronous electric motors are of two types: squirrel-cage and phase rotor.

Household appliances, such as a fan or a vacuum cleaner, are usually equipped with squirrel-cage motors, which is a "squirrel wheel". All rods are closed with discs welded on both sides. The interaction of the stator magnetic field with the induced currents in the rotor forms an electromagnetic force that acts on the rotor in the direction of rotation of the stator field. The torque on the motor shaft is created by all the electromagnetic forces from each conductor.

In the electric motor with a phase rotor, the same stator is used as for the motor with a squirrel-cage rotor. And windings are added to the rotor three phases connected in a star. When starting the engine, they can be connected to rheostats that regulate starting currents. With the help of rheostats, you can also adjust the engine speed.

The advantages of asynchronous motors include:

Powered directly from AC mains.
Simplicity of the device and relatively low cost.
Possibility of use in household appliances using a single-phase connection.
Low energy consumption and economical.

Serious disadvantages are complex speed control and large heat losses. To prevent overheating, the body of the unit is ribbed, and an impeller for cooling is installed on the motor shaft.

The difference in the characteristics of electric motors

Design features and performance characteristics of electric motors are crucial when choosing units. The design of transmissions and all power units of mechanisms depends on this. When choosing an engine, you need to rely on the commonality and main differences in the properties of the machines:

The main difference between a synchronous and asynchronous motor is the design of the rotor. It is a permanent or electric magnet. At the asynchronous magnetic fields in the rotor are induced using electromagnetic induction.
For synchronous motors, the shaft speed is constant, for asynchronous motors, it can change when the load changes.
Synchronizers have no starting torque. To enter synchronization, you need to use asynchronous start.

Synchronous and asynchronous electric motors each find their own application. Synchronous motors are recommended to be used everywhere at high powers, where there is a continuous manufacturing process and you do not need to frequently restart the units or adjust the speed. They are used in conveyors, rolling mills, compressors, stone crushers, etc. A modern synchronous motor has the same quick launch, like asynchronous, but it is smaller and more economical than asynchronous, equal in power.

Asynchronous motors with a phase rotor are used where a large starting torque is needed and frequent stops aggregates. For example, in elevators and tower cranes. Asynchronous electric motors with a squirrel-cage rotor are widely used due to the simplicity of the device and ease of operation.

Using the advantages of different units and how a synchronous motor differs from an asynchronous one, you can make a reasonable choice of one or another motor when designing machines, machine tools and other equipment.

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Figure 7.7 shows the characteristics of synchronous motors SDV 17-39-12 and SDV-17-59-12 (C - synchronous, D - motor, B - for driving fans, 17 - overall, 39 and 59 - stator core length, cm , 12 - number of poles) and VDS 325/49-16. The characteristics of synchronous motors (Fig. 7.7) have a number of advantages compared to the characteristics,:
the ability to work with a leading power factor;
lower losses;
synchronous rotation regardless of the load;
the possibility of smooth regulation of reactive power and more high quality in load nodes;
the ability to maintain stable operation during fluctuations in the supply network.
Last Feature due to the fact that for a synchronous motor the maximum torque is proportional to the voltage, and for the AD - to the square - Fig. 7.4.

Synchronous motors, along with the presence of an excitation winding on the rotor, also have a powerful damper system that provides starting and acceleration of the rotor to a subsynchronous speed in asynchronous mode, with an excitation winding closed to damping resistance. Upon reaching the subsynchronous speed, the engine is synchronized by turning on the AGP and bringing its speed to synchronous. Synchronization becomes more complicated at high engine load factors, and there are no unloading possibilities for the synchronization period in the auxiliary needs system of power plants - Fig. 7.7.
The disadvantage of synchronous electric motors is the need to turn off the AGP and transfer them to asynchronous mode even with short-term deep drops in the supply voltage associated with non-remote and erroneous shutdown of the working power inputs. When using synchronous motors in power plants, they will participate in self-starting along with other asynchronous motors under conditions of lower supply voltages compared to starting a separate one. In this case, the synchronization conditions become more complicated.

Based on the high sensitivity of synchronous motors to deep voltage drops, the difficulty of synchronization in self-starting conditions, the absence of the need for reactive power compensation in the MV system due to the small distance of synchronous generators, synchronous motors have found limited use in the MV system of power plants. Synchronous motors are used to power consumers that do not affect the immediate shutdown technological process: Part circulation pumps, drives of compressors and fans, mills, crushers. The listed mechanisms usually have intermediate fuel bunkers and reserves of the pumped working fluid in the receivers.
As an example, Table 7.2 shows a fan mill with a drive synchronous motor brand SDMZ2-22-61-40UHL4, designed to drive ball and rod mills. In type designation:
C - synchronous, D - motor, M - for driving mills, Z - closed version, 2 - second series, 22 - overall size, 61 - stator core length, cm, 40 - number of poles, UHL4 - climatic version and placement category according to GOST . Starting the motor is asynchronous direct at rated mains voltage with the inclusion of discharge resistance in the excitation winding circuit. During the starting process, the average at the motor terminals must be at least 0.85Unom, the minimum at the start of the start must be at least 0.8Unom. The engine allows two starts in a row from a cold state or one start from a hot state, provided that the average static moment of resistance of the mechanism on the shaft during the start does not exceed 0.8M nom, with the moment of inertia of the driven mechanism not more than that specified in Table 7.2. The motor is excited by thyristor exciters. We pay attention to the low speed of rotation of electric motors of the SDMZ2 series within 100 - 150 rpm, for which asynchronous motors are not produced.

The rotor moves "by itself". It initially has no magnetic field, no electrical voltage is applied to it. It does not even have to be made of iron - a magnetic metal. Well, come on, it’s worth connecting a three-phase voltage to the motor, and the rotor spins. Without any push. But in my own way.

Two kinds of AC motors

Induction motors - naive simplicity

Synchronous motors: complex in simple

There are two options. Either this is a field from a permanent magnet fixed in the rotor, or this is a field from electromagnets installed in the rotor instead of such a magnet.

1 - rotor,
2 - excitation collector

However, among other things, a synchronous motor has the property of complete reversibility. Because a synchronous electric motor is the same electric current generator, but working "in the opposite direction." In the generator, some mechanical force rotates the shaft with the rotor, and from this, an induced electrical voltage arises in the stator windings from the rotating magnetic field of the rotor. And the difference between a synchronous motor and a generator is that the voltage in the stator coils generates a magnetic field running in a circle, which, interacting with the constant magnetic field of the rotor, pushes it so that the rotor also rotates.

Differences and disadvantages of these engines

An asynchronous motor differs from a synchronous motor in the following parameters:

simplicity of design and low cost;
no sliding contacts, reliable operation;
voltage is applied to the fixed stator coils;
the rotor is very simple in design;
when starting and accelerating, it gradually increases power;
the ability to reverse the direction of rotation by simply swapping two supply phases;
when the movement stops (too much mechanical load on the rotor shaft), no accident occurs, the squirrel cage may overheat.

The differences between a synchronous motor and an asynchronous motor are as follows:

stable rotation speed regardless of the load on the shaft;
low sensitivity to voltage drops in the network;
when the mechanical load is reduced, it is able to work as a generator by inertia, not taking energy, but giving it to the network;
high efficiency;
able to compensate for the reactive power of the network.

But each has its own disadvantages.

Asynchronous has the following negative traits:

difficulty adjusting the speed;
low speed;
dependence of the speed lag on the axle load;
during operation, the rotor heats up due to short-circuited currents - additional cooling is required.

Disadvantages of a synchronous motor: