We understand the principles of operation of electric motors: the advantages and disadvantages of different types. We understand in the principles of the operation of electric motors: the advantages and disadvantages of different types of laboratory work 10 Study of the electric motor
current "Place of lesson B. working program: 55 lesson, one of the lessons of the topic "Electromagnetic phenomena".
The purpose of the lesson: Explain the device and the principle of operation of the electric motor.
Tasks:
examine the electric motor using the practical method - the execution of laboratory work.
learn to apply the knowledge gained in non-standard situations to solve problems;
for the development of thinking of students to continue the development of mental analysis, comparisons and synthesis operations.
continue the formation of cognitive interest of students.
Methodical goal:the use of health-saving technologies in physics lessons.
Work forms and activities in the lesson: Check knowledge taking into account individual characteristics of students; Laboratory work is carried out in microGroups (pairs), actualization of knowledge of students in a game form; Explanation of the new material in the form of a conversation with demonstration experiments, goaling and reflection.
During the classes
1) Checking homework.
Independent work (multi-level) is carried out during the first 7 minutes of the lesson.
Level 1.
2 level.
3 level.
2). Studying a new material. (15 minutes).
The teacher reports the subject of the lesson, students form a goal.
Actualization of knowledge. Game "Yes" and "No"
The teacher reads the phrase if the disciples agree with the statement they get up if not - sit.
The magnetic field is formed by permanent magnets or electric shock.
There are no magnetic charges in nature.
The south pole of the magnetic arrow indicates the south geographical pole of the Earth.
The electromagnet is called a coil with an iron core inside.
The power lines of the magnetic field are directed from left to right.
Lines along which magnetic arrows are installed in the magnetic field are called magnetic lines.
Outlines.
The magnetic field action on the conductor with a current.
The dependence of the direction of movement of the conductor from the direction of the current in it and on the location of the poles of the magnet.
Device and action of the simplest collector electric motor.
Movement of the conductor and frame with a current in a magnetic field.
Device and principle of operation of the electric motor direct current.
Safety Instructions.
The work is performed according to the description in the textbook page 176.
4Concluding stage of the lesson.
A task. Two electron beams are repelled, and two parallel wires for which the current flow in one direction is attracted. Why? Is it possible to create conditions under which these conductors will also be repelled?
Reflection.
What new learned? Do you need these knowledge in everyday life?
Questions:
What does the rotor rotation speed in the electric motor depends?
What is called an electric motor?
P . 61, make a crossword puzzle on the topic "Electromagnetic phenomena.
Application.
Level 1.
1. How interacts the varied and eponymous poles of magnets?
2. Is it possible to cut a magnet so that one of the obtained magnets only had the North Pole, and the other is only South?
2 level.
Why is the compass case made from copper, aluminum, plastics and other materials, but not iron?
Why are steel rails and stripes lying in stock, after some time turn out to be magnetized?
3 level.
1. Draw the magnetic field of the horseshoe magnet and indicate the direction of power lines.
2. Two pins attracted the southern pole of the magnet. Why are their free ends repel?
Level 1.
1. How interacts the varied and eponymous poles of magnets?
2. Is it possible to cut a magnet so that one of the obtained magnets only had the North Pole, and the other is only South?
2 level.
Why is the compass case made from copper, aluminum, plastics and other materials, but not iron?
Why are steel rails and stripes lying in stock, after some time turn out to be magnetized?
3 level.
1. Draw the magnetic field of the horseshoe magnet and indicate the direction of power lines.
2. Two pins attracted the southern pole of the magnet. Why are their free ends repel?
MKOU "Allak School"
Open physics lesson in grade 8 on the topic " The magnetic field action on the conductor with a current. Electrical engine. Laboratory work number 9 "Study of the electrical engine of permanent current.
Prepared and held: Teacher of the first category Taranushenko Elizabeth Aleksandrovna.
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.
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.
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.
Any electric motor is designed for making mechanical work Due to the consumption of electricity applied to it, which is converted, as a rule, into a rotational movement. Although the technique there are models that immediately create the translational movement of the worker. They are called linear engines.
In industrial installations, the electromotors act as various machines and mechanical devices involved in the technological production process.
Inside household appliances Electric motors work B. washing machines, vacuum cleaners, computers, hairdo, children's toys, clocks and many other devices.
The main physical processes and principle of operation
On moving inside electric chargeswhich is called electric shock, mechanical force always acts, seeking to deflect their direction in the plane located perpendicular to the orientation of magnetic power lines. When electricity It passes through the metal conductor or made of it the coil, then this force seeks to move / turn each conductor with current and the entire winding in general.
The picture below shows the metal frame for which the current flows. The magnetic field applied to it creates for each branch of the frame strength F, creating 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 laid in the operation of any electric motor. It includes:
the winding on which electric current flows. It is located on a special core-anchor and fastened in the rotational bearings to reduce the opposition of friction forces. This design is called the rotor;
a stator that creates a magnetic field that its power lines permeates the electric charges passing the rotor windings;
case for stator placement. Special landing nests are made inside the case, inside which the outer coat of rotor bearings are mounted.
Simplified design of the simplest electric motor can be represented by a picture of the next species.
When rotating the rotor, a torque is created, the power of which depends on the overall design of the device, the values \u200b\u200bof the applied electrical energy, its losses during conversion.
The magnitude of the maximum possible power of the engine torque is always less than the electrical energy applied to it. It is characterized by the magnitude of the efficiency.
Types of electric motors
According to the current windings, they are divided into direct or alternating currents. Each of these two groups has a large number of modifications using various technological processes.
DC electric motors
They have a magnetic field of the stator is created stationaryly fixed or special electromagnets with excitation windings. The anchor winding is rigidly mounted into the shaft, which is fixed in the bearings and can freely rotate around its own axis.
The principal device of such an engine is shown in the figure.
A winding consisting of two consecutively connected parts is located on the conductive anchors of ferromagnetic materials, which are connected to the conductive collector plates in one end, while the other is uncrowed with each other. Two brushes from graphite are located on the diametrically opposite ends of the anchors and pressed to the contact plates.
The positive potential of the constant source of current is supplied to the lower brush, and the top is negative. The direction of the current winding is shown by a dotted red arrow.
The current causes the magnetic field of the North Pole in the lower left part of the anchor, and in the right-to-top - the southern (the rule of the bull). This leads to repulsion of the poles of the rotor from the stationary of the same name and attraction to the variepete poles on the stator. As a result of the applied force, a rotational movement occurs, the direction of which indicates a brown arrow.
With further rotation of the anchor anchor on the inertia, the poles go to other collector plates. The current direction in them varies to the opposite. The rotor continues further rotation.
A simple design of a similar collector device leads to large losses of electrical energy. Similar engines operate in simple design devices or toys for children.
DC electric motors involved in the production process have a more complex design:
the winding is not two, but for a larger number of parts;
each section of the winding is mounted on its pole;
the collector device is performed by a certain number of contact pads by the number of windings sections.
As a result, a smooth connection of each pole is created through its contact plates to brushes and a current source, electricity losses are reduced.
The device of this anchor is shown in the picture.
In electrical DC motors, you can reverse the direction of rotation of the rotor. To do this, it is enough to change the flow of current in the winding to the opposite polarity shift at the source.
AC electric motors
They differ from the previous structures by the fact that the electric current flowing in their winding is described by by periodically changing its direction (sign). For their power, the voltage is supplied from generators with a sign-hot value.
The stator of such engines is performed by the magnetic circuit. It is made of ferromagnetic plates with grooves in which the winding coils are placed with the configuration of the frame (coil).
Synchronous electric motors
The picture below shows principle of operation of a single-phase AC motor With synchronous rotation of electromagnetic fields of the rotor and stator.
In the grooves of the stator magnetic pipeline in diametrically opposite ends, the winding conductors are placed, schematically shown in the form of a frame, which flows alternating current.
Consider the case for the moment of time corresponding to the passage of the positive part of its half-wave.
A rotor with an elevated permanent magnet, which is pronounced by the northern "n mouth" and the southern "s mouth" of the pole, is freely rotated in the bearing walls. When the positive half-wave current over the stator winding, it creates a magnetic field with Poles "S ST" and "N Art".
Between the magnetic fields of the rotor and the stator, the interaction forces arise (the poles of the same name are repelled, and the variepetes are attracted), which seek to rotate the anchor of the electric motor from an arbitrary position in the final one when the opposite poles are as follows.
If we consider the same case, but for the moment when the reverse - negative half-wave current flows on the frame conductor, the anchor rotation will occur in the opposite direction.
To give continuous motion, the rotor in the stator makes not one winding frame, but a certain amount of their amount with such accounting so that each of them is fed from a separate current source.
Principle of operation of the three-phase AC motor with synchronous rotationelectromagnetic rotor and stator fields are shown in the following picture.
In this design, three windings A, B and C, shifted to the angles of 120 degrees, are mounted within the stator magnetic pipeline. Winding A is highlighted in yellow, in green, and with - red. Each winding is made by the same frames as in the previous case.
In the picture for each case, the current passes only on one winding in the forward or reverse direction, which is shown the "+" and "-" icons.
When the positive half-wave passes in phase, and in the forward direction, the axis of the rotor field occupies a horizontal position because the magnetic poles of the stator are formed in this plane and attract moving anchor. Rotor's varieve poles seek to get closer to the poles of the stator.
When a positive half-wave goes in phase C, then the anchor turns 60 degrees along the clockwise arrow. After the current is supplied to the phase in a similar armature turn. Each regular current flow in the next phase of the next winding will rotate the rotor.
If there is a three-phase voltage shifted over the angle of 120 degrees to each winding, then alternating currents will be circulated, which will promote anchor and create its synchronous rotation with the subordinate electromagnetic field.
The same mechanical design is successfully used in three-phase stepping motor. Only in each winding with control, direct current pulses are fed and removed according to the algorithm described above.
Their starts starts the rotational movement, and the termination at a certain point in time provides a dosage rotation of the shaft and stop to the programmed angle to perform certain technological operations.
In both described three-phase systems, it is possible to change the direction of rotation of the anchor. To do this, it is necessary to simply change the alternation of the phases "A" - "B" - "C" to another, for example, "A" - "C" - "B".
The rotation speed of the rotor is regulated by the period of the period, the reduction leads to the acceleration of rotation. The magnitude of the amplitude of the current in the phase depends on the internal resistance of the winding and the value of the voltage applied to it. It defines the magnitude of the torque and power of the electric motor.
Asynchronous electric motors
These engine designs have the same stator magnetic core with windings, as in previously considered single-phase and three-phase models. They obtained their name due to incomprehensible rotation of electromagnetic fields of the anchors and the stator. This is done by improving the rotor configuration.
Its core is dialed from plates electrical steel stamps with grooves. Aluminum or copper toxes are mounted in them, which at the ends of the anchors are closed by conductive rings.
When voltage is supplied to the stator windings, the electric current is covered in the rotor winding of the rotor, and the anchor magnetic field is created. When the interaction of these electromagnetic fields, the engine shaft rotation begins.
This design has a rotor movement only after a rotating electromagnetic field has occurred in the stator and it continues in incommary mode of operation with it.
Asynchronous motors are easier in constructive design. Therefore, they are cheaper and massively used in industrial installations and household household appliances.
Linear electric motors
Many working bodies of industrial mechanisms perform a reciprocating or translational movement in one plane required for the operation of metalworking machines, vehicles, hammer blows when scoring piles ...
Moving such a working body using gearboxes, balls, belt gears and similar mechanical devices From the rotational motor complicates the design. Modern technical solution This problem is the operation of a linear electric motor.
He has a stator and the rotor stretched in the form of strips, and not rolled rings, like rotational electric motors.
The principle of operation consists in making a reciprocating linear movement by the Rotor runner due to the transfer of electromagnetic energy from a fixed stator with an unclosed magnetic core of a certain length. Inside it, a tanning magnetic field is created by alternate turning on the current.
It affects an anchor winding with a collector. The forces arising in such an engine move the rotor only in the linear direction along the guide elements.
Linear engines are designed to work on a constant or alternating current, can operate in synchronous or asynchronous mode.
The disadvantages of linear engines are:
complexity of technology;
high price;
low energy indicators.
1. Objective: Examine the launch features, mechanical characteristics and methods for regulating the frequency of rotation of the DC motor with a mixed excitation.
Adoption.
2.1. To independent work:
Explore the design features, the DC motor circuit on;
Study the methodology for obtaining the mechanical characteristics of the DC motor;
Familiarize yourself with the features of starting and regulating the frequency of rotation of the DC motor;
Draw schemes To measure the resistances of the chain of the anchor and the excitation windings (Fig.6.4) and the engine tests (Fig.6.2);
Using Fig. 6.2 and 6.3 Make a mounting scheme;
Draw the forms of tables 6.1 ... 6.4;
Prepare oral answers to check questions.
2.2. To work in the laboratory:
Familiarize yourself with the laboratory installation;
Record in Table 6.1. Engine passport data;
Measure the resistance of the chain of the anchor and the windings of the excitation. The data is recorded in Table 6.1;
Collect the scheme and conduct engine research, write data to Tables 6.2, 6.3, 6.4;
Construct a natural mechanical characteristic n \u003d f (m) and high-speed characteristics n \u003d f (i b) and n \u003d f (u);
Make conclusions based on the results of the study.
General.
DC motors Unlike AC motors (primarily asynchronous) have greater multiplicity of starting torque and overload capacity, provide smooth control of the rotational speed of the working machine. Therefore, they are used to drive machines and mechanisms with severe launch conditions (for example, as starters in internal combustion engines), as well as if necessary, regulating the speed of rotation in high limits (machine tool mechanisms, trimmed-brake stands, electrified vehicles).
Structurally, the engine consists of a fixed assembly (inductor) and a rotating node (anchor). At the inductor magnetic circuit breeding, excitation windings are located. In the engine of mixed excitation, there are two of them: parallel with the conclusions W 1 and C2 and sequential with the conclusions C1 and C2 (Fig. 6.2). The resistance of the parallel winding R OVS is depending on the engine power from several tens to hundreds. It is made with a small cross section with large number turns. Sequential winding has a small resistance R OBC (usually from several Ohm to the share of Ohm), because Consists of a small number of turns of a large cross section. The inductor serves to create a magnetic flux of excitation when the dock windings is powered.
The anchor winding is placed in the grooves of the magnetic pipeline and is removed on the collector. With the help of brushes, its conclusions I I and I 2 are connected to a DC source. Resistance to the winding of the anchor R I am small (Omms or the share of Ohm).
The rotating moment M of the DC motor is created when the interaction of the anchor anchor I with the magnetic flux of the F:
M \u003d K × Iia × F, (6.1)
where K is a permanent coefficient depending on the engine design.
When rotating an anchor, the winding crosses the magnetic flux of the excitation and the EDC E is induced, proportional to the rotation frequency N:
E \u003d C × n × F, (6.2)
where C is a permanent coefficient depending on the engine design.
Current in the chain of the anchor:
I \u003d (U-E) / (R + R oats) \u003d (u-s × n × f) / (r i + R oats), (6.3)
Solving together expressions 6.1 and 6.3 relative to P, find an analytical expression of the mechanical characteristics of the engine n \u003d f (m). Her graphic image shown in Figure 6.1.
Fig. 6.1. Mechanical characteristics of a DC motor of mixed excitation
Point A corresponds to the operation of the engine in a frequency of rotation N about. With an increase in the mechanical load, the speed of rotation is reduced, and the torque increases, reaching at the point in the nominal value M H. In the plot of the aircraft, the engine works with overload. The current I is greater than the nominal value, which leads to a rapid heating of the windings of the anchor and ABS, increases sparking on the collector. The maximum moment M M M (point C) is limited by the conditions of the manifold and the mechanical strength of the engine.
Continuing the mechanical characteristic before the intersection at the point D "With the axis of the torque, we would get the value of the starting point with the direct turning on the engine into the network. EMF E is zero and current in the anchor chain in accordance with formula 6.3 increases sharply.
To reduce the start current, in series, the armature circuit includes the RX launcher (Fig. 6.2) with resistance:
RX \u003d U H / (1.3 ... 2.5) × i n. - (R I - R OBC), (6.4)
where u h is the rated voltage of the network;
I Ya.N. - Nominal anchor current.
Reduced anchor current to (1.3 ... 2.5) × i n. Provides a sufficient initial starting point MP (point d). As the engine is accelerated, the resistance rx is reduced to zero, maintaining an approximately constant MP (SD section).
Reostat R B in the circuit of the parallel excitation winding (Fig. 6.2) allows you to adjust the magnetic flux value F (formula 6.1). Before starting the engine, it is completely displayed to obtain the necessary starting torque with minimal anchor current.
Using formula 6.3, we define the engine rotation frequency
n \u003d (U - I (R I + R OBC + RX)) / (with f), (6.5)
in which R I, R OBC and C are constant values, and u, I I and F can be changed. Three follows from here possible method Engine rotation frequency control:
A change in the value of the supply voltage;
A change in the values \u200b\u200bof the anchor current using the RX adjustment RX, which, unlike the launcher, is calculated on the continuous operation mode;
By changing the magnetic flux of the excitation F, which is proportional to the current in the windings of ORS and ABS. In the parallel winding, it can be adjusted by the R B to the r b. The resistance R B is taken depending on the required limits of regulating the rotational speed R B \u003d (2 ... 5) R OBSH.
The engine's passport plate indicates the rated rotation frequency, which corresponds to the rated power on the motor shaft at the rated voltage of the network and the revealed resistances of R x and R b.
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.
The principle of operation of the DC electric motor is the effect of repulsion of the same name poles of permanent magnets and attracting multi-dimensional. 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 of active resistance in an anchor chain. 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 life modern societyFounded on high technologies, and something more efficient is not yet invented.
Synchronous principle of operation of the electric motor