We understand the principles of operation of electric motors: the advantages and disadvantages of different types. We understand in the principles of operation of electric motors: the advantages and disadvantages of different types of study of the DC electric motor

The electric motor is an electrical device for transforming electrical energy into mechanical. Today, electric motors in industry for drives of various machines and mechanisms are universally used. In the household they are installed in washing machine, refrigerator, juicer, kitchen combine, fans, electric razors, etc. Electric motors are driven by devices connected to it and mechanisms.

In this article, I will talk about the most common types and principles of the operation of electrical AC motors widely used in the garage, in a household or workshop.

How the electric motor works

Engine runs based on effectMichael Faraday was found in 1821. He made the discovery that when interacting electric current In the explorer and magnet, continuous rotation may occur.

If in a homogeneous magnetic field To position the frame in the vertical position and skip over it, then the electromagnetic field will arise around the conductor, which will interact with the poles of magnets. From one frame will be repelled, but to another to attract.

As a result, the frame will turn into a horizontal position in which the impact of the magnetic field on the conductor will be zero. In order to continue the rotation, you must add another frame at an angle or change the current direction in the frame at the right moment.

In the figure, this is done using two semi-colts, to which the contact plates are adjacent to the battery. As a result, after committing a half-timer, polarity changes and rotation continues.

In modern electric motors Instead of constant magnets, inductors or electromagnets are used to create a magnetic field. If you disassemble any motor, you will see wrapped wire coated with insulating varnish. These turns are electromagnet or as they also call the excitation winding.

At home same permanent magnets are used in children's toys on batteries.

In the other more powerfulengines are used only electromagnets or windings. The rotating part with them is called the rotor, and a fixed stator.

Types of electric motors

Today there are quite a few electric motors of different designs and types. They can be divided by the type of power:

Alternating currentworking directly from the power grid.
Direct currentthat work from batteries, battery, power supplies or other DC sources.

According to the principle of operation:

Synchronousin which there are windings on the rotor and the brush mechanism for supplying electrical current on them.
Asynchronous, the easiest and most common type of motor. They do not have brushes and windings on the rotor.

The synchronous motor rotates synchronously with the magnetic field, which rotates it, and the asynchronous rotor rotates a slower rotating magnetic field in the stator.

Principle of operation and device of an asynchronous electric motor

In the asynchronous housing The engine stacked windings (for 380 volts there will be 3), which create a rotating magnetic field. The ends of them are displayed on a special terminal block. Winding cooled, thanks to the fan installed on the shaft in the end of the electric motor.

Rotorwhich are one with the shaft, is made of metal rods that are closed with each other from both sides, so it is called short-circuited.
Thanks to this design, there is a need for frequent periodic maintenance and replacement of current brushes, reliability, durability and reliability increase repeatedly.

Usually, the main cause of breakage Asynchronous motor is the wear of bearings in which the shaft rotates.

Principle of operation. In order to work asynchronous engine, it is necessary that the rotor would rotate a slower electromagnetic field of the stator, as a result of which the EMF is guided (electrotes arises) in the rotor. Here is an important condition, if the rotor rotated at the same speed as the magnetic field, then the EMF would not have been guided by the law of electromagnetic induction and, therefore, there would be no rotation. But in reality, due to friction of bearings or load on the shaft, the rotor will always rotate slower.

Magnetic poles constantly rotate In the windings of the motor, and the current direction in the rotor is constantly changing. At one point in time, for example, the direction of currents in the windings of the stator and the rotor is shown schematically in the form of crosses (current flows from us) and points (current on us). The rotating magnetic field is depicted porter.

For example, how Circular Saw works. She has the greatest turnover. But as soon as we begin to cut the board, the speed of rotation decreases and at the same time with this the rotor begins to rotate more slowly relative to the electromagnetic field and in it, according to the laws, electrical engineering begins to the even greater magnitude of the EMF. Grow current consumed by the motor and it begins to work at full power. If the load on the shaft is so great that it is strooped, then damage to the short-circuit rotor may occur due to the maximum value of the EDC in it. That is why it is important to pick the engine suitable power. If you take more, then energy consumption will be unjustified.

Rotor rotation speed Depends on the number of poles. With 2 poles, the rotation speed will be equal to the speed of rotation of the magnetic field equal to a maximum of 3000 revolutions per second at a network frequency of 50 Hz. To lower the speed halve, it is necessary to increase the number of poles in the stator to four.

Weight lack of asynchronous The engines are that they are fed by adjusting the rotational speed of the shaft only with changing the frequency of the electric current. And it is not possible to achieve a constant frequency of rotation of the shaft.

Principle of operation and device of a synchronous electric motor of alternating current

This type of electric motor is used in everyday life where it is necessary permanent speed Rotation, the possibility of its adjustment, as well as if the speed of rotation is more than 3000 revolutions per minute (this is a maximum for asynchronous).

Synchronous motors are installed in the power tool, vacuum cleaner, washing machine, etc.

In the synchronous housing The AC motor is located (3 in the figure), which are also wound on the rotor or anchor (1). Their conclusions are soldered to the sectors of the current-point ring or collector (5), which is supplied with a graphite brushes (4). The conclusions are located so that the brushes always supply voltage only one pair.

The most frequent breakdowns Collector engines is:

Wear brushesor their poor contact of their contact due to the weakening of the clamping spring.
Pollution collector.Clean either alcohol or zero sandpaper.
Bearing wear.

Principle of operation. The torque in the electric motor is created as a result of the interaction between the current anchor current and the magnetic flux in the excitation winding. With a change in the direction of alternating current, the direction of the magnetic flux will also change simultaneously in the case and anchor, due to which the rotation will always be one way.

Electric motors are devices in which electrical energy turns into mechanical. The principle of their action is the phenomenon of electromagnetic induction.

However, methods of interaction of magnetic fields forcing the engine rotor rotate significantly vary depending on the type of supply voltage - alternating or permanent.

At the basis of the principle of operation of the electric motor direct current It is the effect of repulsing the same poles of permanent magnets and attracting varies. The priority of its invention belongs to the Russian engineer B. S. Yakobi. The first industrial model of the DC motor was created in 1838. Since then, its design has not undergone fundamental changes.

In DC engines of low power, one of the magnets is physically existing. It is fixed directly on the machine housing. The second is created in the anchor winding after connecting the DC source to it. To do this, use a special device - a collector-brush node. The collector itself is a conductive ring, fixed on the engine shaft. The ends of the anchor winding are connected to it.

To the torque, it is necessary to continuously change the pole of the permanent magnet anchor. This should occur at the time of the intersection of the so-called magnetic neutral. Constructively, such a task is solved by the division of the collector ring to the sectors separated by dielectric plates. Ends of the windings of the anchors join them alternately.

To connect a collector with a supply network, the so-called brushes are used - graphite rods having high electrical conductivity and a small sliding friction coefficient.

Anchor windings are not connected to the supply network, and by means of a collector-brush node are connected to a starting row. The process of incorporating such an engine consists of a compound with a supply network and a gradual decrease to zero active resistance In the chain of the anchor. The electric motor is switched on smoothly and without overload.

Features of using asynchronous engines in a single-phase chain

Despite the fact that the rotating magnetic field of the stator is the easiest way to obtain from three-phase voltage, the principle of the action of an asynchronous electric motor allows it to work on a single-phase, household network if some changes will be made to their design.

To do this, there must be two windings on the stator, one of which is "starting". The current in it is shifted in phase by 90 ° due to the inclusion in the chain of the reactive load. Most often for this

Practically complete synchronicity of magnetic fields allows the engine to gain momentum even with significant loads on the shaft, which is required for the operation of drills, perforators, vacuum cleaners, "Bulgarians" or polywood machines.

If the controlled circuit of such an engine is enabled, the frequency of its rotation can be smoothly changed. But the direction, when nutrition from the AC circuit, will never be able to change.

Such electric motors are able to develop very high revs, compact and have a larger torque. However, the presence of a collector-brush node reduces their motor expansion - graphite brushes are quickly abrained at high revs, especially if the collector has mechanical damage.

Electric motors have the largest efficiency (more than 80%) of all devices created by man. Their invention at the end of the XIX century can well be considered a high-quality civilization jump, because without them it is impossible to imagine the life of modern society based on high technologiesand something more efficient is not yet invented.

Synchronous principle of operation of the electric motor

Laboratory works → Number 10

Study of the electrical motor of DC (on the model).

Purpose of work:Get acquainted with the main parts of the DC electric motor on the model of this engine.

This is perhaps the most simple job for grade 8. You just need to connect the engine model to the current source, see how it works, and remember the names of the main parts of the electric motor (anchor, inductor, brushes, semiring, winding, shaft).

The electric motor proposed by the teacher can be similar to the picture shown in the figure, and may have a different look, since school electric motors there are many. It does not have a fundamental importance, since the teacher will surely tell in detail and show how to handle the model.

We list the main reasons for the correctly connected electric motor does not work. Circuit break, no contact brushes with semirings, damage to the winding of the anchor. If in the first two cases you are completely able to cope on your own, in the event of a cliff, the windings should be referred to as a teacher. Before turning on the engine, make sure that its anchor can freely rotate and does not interfere with it, otherwise, when the electric motor will be turned on, it will not be a characteristic buzz, but there will be no rotation.

Task condition: Laboratory work number 10. Study of the electric DC motor (on the model).

Task out
Reshebnik in physics, grade 8, A.V. Pereyshkin, N.A.Rodina
For 1998.
Online reshebnik in physics
for grade 8.
Laboratory works
- number
10

Study of the electrical motor of DC (on the model).

The purpose of the work: familiarize yourself with the main parts of the DC electric motor on the model of this engine.

Do not know how to solve? Can you help with the solution? Come and ask.

← Laboratory work number 9. Assembly of an electromagnet and testing of its action. Laboratory work number 11. Getting an image with lenses.

Laboratory work number 9

Subject. Study of the DC motor.

Purpose of work: Examine the device and the principle of operation of the electric motor.

Equipment: Motor model, current source, retain, key, ammeter, connecting wires, drawings, presentation.

TASKS:

1 . Explore the device and the principle of operation of the electric motor using the presentation, drawings and model.

2 . Attach the electric motor to the current source and watch it. If the engine does not work, set the cause, try to eliminate the problem.

3 . Specify the two main elements in the electric motor device.

4 . What physical phenomenon is based on the action of an electric motor?

5 . Change the direction of rotation of the anchor. Write down what needs to be done for this.

6. Collect electric chainBy connecting a sequentially motor, a retail, a current source, an ammeter and key. Change the current strength and watch the operation of the electric motor. Does the speed of rotation of the anchor change? Record the conclusion about the dependence of the force acting from the magnetic field to the coil, from the strength of the current in the coil.

7 . Electric motors can be any power, because:

A) you can change the strength of the current in the winding of the anchor;

B) You can change the magnetic field of the inductor.

Specify the correct answer:

1) is true only a; 2) is true only b; 3) true and a, and b; 4) incorrectly A, and B.

8 . List the advantages of the electric motor compared to the thermal engine.