We understand the principles of operation of electric motors: the advantages and disadvantages of different types. We understand the principles of operation of electric motors: the advantages and disadvantages of different types Laboratory work studying the operation of a DC electric motor

Electric motors have the highest efficiency (more than 80%) of all devices created by man. Their invention at the end of the 19th century can be considered a qualitative leap in civilization, because without them it is impossible to imagine the life of a modern society based on high technology, and something more effective has not yet been invented.

Synchronous principle of operation of an electric motor on video

Laboratory works→ number 10

Study of a DC electric motor (on a model).

Goal of the work: Familiarize yourself with the basic parts of a DC electric motor using a model of this motor.

This is perhaps the easiest work for the 8th grade course. You just need to connect the motor model to a current source, see how it works, and remember the names of the main parts of the electric motor (armature, inductor, brushes, semi-rings, winding, shaft).

The electric motor offered to you by your teacher may be similar to the one shown in the figure, or it may have a different appearance, since there are many options for school electric motors. This is not of fundamental importance, since the teacher will probably tell you in detail and show you how to handle the model.

Let us list the main reasons why a properly connected electric motor does not work. Open circuit, lack of contact of brushes with half rings, damage to the armature winding. If in the first two cases you are quite capable of handling it on your own, if the winding breaks, you need to contact the teacher. Before turning on the engine, you should make sure that its armature can rotate freely and nothing interferes with it, otherwise when turned on, the electric motor will emit a characteristic hum, but will not rotate.

Laboratory work No. 9

Subject. Study of DC electric motor.

Goal of the work: study the structure and principle of operation of an electric motor.

Equipment: electric motor model, current source, rheostat, key, ammeter, connecting wires, drawings, presentation.

TASKS:

1 . Study the structure and principle of operation of an electric motor using a presentation, drawings and a model.

2 . Connect the electric motor to a power source and observe its operation. If the engine does not work, determine the cause and try to fix the problem.

3 . Indicate the two main elements in the design of an electric motor.

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

5 . Change the direction of rotation of the armature. Write down what you need to do to achieve this.

6. Assemble an electrical circuit by connecting an electric motor, rheostat, current source, ammeter and switch in series. Change the current and observe the operation of the electric motor. Does the speed of rotation of the armature change? Write down a conclusion about the dependence of the force acting on the coil from the magnetic field on the current strength in the coil.

7 . Electric motors can be of any power, because:

A) you can change the current strength in the armature winding;

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

Please indicate the correct answer:

1) only A is true; 2) only B is true; 3) both A and B are true; 4) both A and B are incorrect.

8 . List the advantages of an electric motor over a thermal engine.

Any electric motor is designed to perform mechanical work due to the consumption of electricity applied to it, which is converted, as a rule, into rotational motion. Although in technology there are models that immediately create a translational movement of the working body. They are called linear motors.

In industrial installations, electric motors drive various machines and mechanical devices involved in the technological production process.

Inside household appliances electric motors operate in washing machines, vacuum cleaners, computers, hair dryers, children's toys, watches and many other devices.

Basic physical processes and principle of operation

On the moving ones inside electric charges, which are called electric current, there is always a mechanical force that tends to deflect their direction in a plane located perpendicular to the orientation of the magnetic lines of force. When electricity passes through a metal conductor or a coil made of it, then this force tends to move/rotate each current-carrying conductor and the entire winding as a whole.

The picture below shows a metal frame through which current flows. The magnetic field applied to it creates a force F for each branch of the frame, creating a rotational motion.

This property of the interaction of electrical and magnetic energy based on the creation of an electromotive force in a closed conductive circuit is involved in the operation of any electric motor. Its design includes:

winding through which electric current flows. It is placed on a special anchor core and secured in rotation bearings to reduce the counteraction of friction forces. This structure is called a rotor;

a stator that creates a magnetic field, which with its lines of force penetrates the electric charges passing through the turns of the rotor winding;

housing for housing the stator. Special mounting sockets are made inside the housing, inside which the outer races of the rotor bearings are mounted.

A simplified design of the simplest electric motor can be represented by the following picture.

When the rotor rotates, a torque is created, the power of which depends on the general design of the device, the amount of applied electrical energy, and its losses during transformations.

The maximum possible torque power of the engine is always less than the electrical energy applied to it. It is characterized by the magnitude of the efficiency factor.

Types of electric motors

Based on the type of current flowing through the windings, they are divided into DC or AC motors. Each of these two groups has a large number of modifications using different technological processes.

DC motors

Their stator magnetic field is created by permanently mounted or special electromagnets with field windings. The armature winding is rigidly mounted in the shaft, which is secured in bearings and can rotate freely around its own axis.

The basic structure of such an engine is shown in the figure.

On the armature core made of ferromagnetic materials there is a winding consisting of two series-connected parts, which are connected at one end to the conductive collector plates, and the other are connected to each other. Two graphite brushes are located at diametrically opposite ends of the armature and are pressed against the contact pads of the commutator plates.

The lower brush of the pattern is supplied with a positive potential of a constant current source, and the upper brush is supplied with a negative potential. The direction of current flowing through the winding is shown by a dotted red arrow.

The current causes a magnetic field of the north pole in the lower left part of the armature, and a south pole in the upper right (gimlet rule). This leads to repulsion of the rotor poles from like stationary poles and attraction to unlike poles on the stator. As a result of the applied force, a rotational movement occurs, the direction of which is indicated by the brown arrow.

With further rotation of the armature, by inertia, the poles move to other collector plates. The direction of the current in them changes to the opposite. The rotor continues to rotate further.

The simple design of such a collector device leads to large losses of electrical energy. Such engines operate in simple devices or toys for children.

DC electric motors involved in the production process have a more complex design:

the winding is sectioned not into two, but into large quantity parts;

each winding section is mounted on its own pole;

The collector device is made of a certain number of contact pads according to the number of winding sections.

As a result, a smooth connection of each pole through its contact plates to the brushes and the current source is created, and electricity losses are reduced.

The device of such an anchor is shown in the picture.

For DC electric motors, the direction of rotation of the rotor can be reversed. To do this, it is enough to reverse the movement of current in the winding by changing the polarity at the source.

AC motors

They differ from previous designs in that the electric current flowing in their winding is described by periodically changing its direction (sign). To power them, voltage is supplied from alternating-sign generators.

The stator of such motors is made of a magnetic circuit. It is made of ferromagnetic plates with grooves into which winding turns with a frame (coil) configuration are placed.

Synchronous electric motors

The picture below shows working principle of single-phase AC motor with synchronous rotation of the electromagnetic fields of the rotor and stator.

In the grooves of the stator magnetic circuit at diametrically opposite ends there are winding conductors, schematically shown in the form of a frame through which alternating current flows.

Let us consider the case for the moment of time corresponding to the passage of the positive part of its half-wave.

A rotor with a built-in permanent magnet rotates freely in the bearing races, which has a clearly defined north “N mouth” and south “S mouth” pole. When a positive half-wave of current flows through the stator winding, a magnetic field with poles “S st” and “N st” is created in it.

Between magnetic fields rotor and stator, interaction forces arise (like poles repel, and opposite poles attract), which tend to rotate the armature of the electric motor from an arbitrary position to a final one, when the opposite poles are located as close as possible relative to each other.

If we consider the same case, but for the moment in time when the reverse - negative half-wave of current flows through the frame conductor, then the rotation of the armature will occur in the opposite direction.

To impart continuous movement to the rotor, not one winding frame is made in the stator, but a certain number of them, taking into account that each of them is powered from a separate current source.

Operating principle of three-phase synchronous rotation AC motor The electromagnetic fields of the rotor and stator are shown in the following picture.

In this design, three windings A, B and C are mounted inside the stator magnetic circuit, shifted at angles of 120 degrees to each other. Winding A is highlighted in yellow, B in green, and C in red. Each winding is made with the same frames as in the previous case.

In the picture, for each case, the current passes through only one winding in the forward or reverse direction, which is shown by the “+” and “-” signs.

When a positive half-wave passes through phase A in the forward direction, the rotor field axis takes a horizontal position because the magnetic poles of the stator are formed in this plane and attract the moving armature. Opposite rotor poles tend to approach the stator poles.

When the positive half-wave follows phase C, the armature will rotate 60 degrees clockwise. After current is supplied to phase B, a similar rotation of the armature will occur. Each successive flow of current in the next phase of the next winding will rotate the rotor.

If a three-phase network voltage shifted at an angle of 120 degrees is supplied to each winding, then alternating currents will circulate in them, which will spin the armature and create its synchronous rotation with the supplied electromagnetic field.

The same mechanical design has been successfully used in three phase stepper motor. Only in each winding, with the help of control, direct current pulses are supplied and removed according to the algorithm described above.

Their start begins a rotational movement, and stopping at a certain point in time ensures a dosed rotation of the shaft and stops at a programmed angle to perform certain technological operations.

In both three-phase systems described, it is possible to change the direction of rotation of the armature. To do this, you just need to change the phase sequence “A” - “B” - “C” to something else, for example, “A” - “C” - “B”.

The speed of rotation of the rotor is regulated by the duration of the period T. Its reduction leads to acceleration of rotation. The magnitude of the current amplitude in a phase depends on the internal resistance of the winding and the value of the voltage applied to it. It determines the amount of torque and power of the electric motor.

Asynchronous electric motors

These motor designs have the same stator magnetic circuit with windings as in the previously discussed single-phase and three-phase models. They got their name due to the non-synchronous rotation of the electromagnetic fields of the armature and stator. This was done by improving the rotor configuration.

Its core is made of electrical grade steel plates with grooves. They are equipped with aluminum or copper current conductors, which are closed at the ends of the armature by conductive rings.

When voltage is applied to the stator windings, an electric current is induced in the rotor winding by an electromotive force and a magnetic field of the armature is created. When these electromagnetic fields interact, the motor shaft begins to rotate.

With this design, rotor movement is possible only after a rotating electromagnetic field has arisen in the stator and it continues in an asynchronous mode of operation with it.

Asynchronous motors are simpler in design. Therefore, they are cheaper and widely used in industrial installations and household appliances.

Linear motors

Many working parts of industrial mechanisms perform reciprocating or translational movement in one plane, necessary for the operation of metalworking machines, Vehicle, hammer blows when driving piles...

Moving such a working body using gearboxes, ball screws, belt drives and similar mechanical devices from a rotary electric motor complicates the design. A modern technical solution to this problem is the operation of a linear electric motor.

Its stator and rotor are elongated in the form of strips, and not folded into rings, like those of rotational electric motors.

The principle of operation is to impart reciprocating linear movement to the runner-rotor due to the transfer of electromagnetic energy from a stationary stator with an open magnetic circuit certain length. Inside it, by alternately turning on the current, a running magnetic field is created.

It acts on the armature winding with the commutator. The forces arising in such an engine move the rotor only in a linear direction along the guide elements.

Linear motors are designed to operate on direct or alternating current and can operate in synchronous or asynchronous mode.

The disadvantages of linear motors are:

complexity of technology;

high price;

low energy levels.