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
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In the figures, determine the direction of the ampere force, the current direction in the conductor, the direction of the magnetic field lines, the magnet pole. N s f \u003d 0 Recall.
Laboratory work number 11 The study of the electrical engine of DC (on the model). The goal of the work is to get acquainted on the DC electric motor model with its device and work. Instruments and materials: Motor Model, Laboratory Power Supply, Key, Connecting Wires.
Safety regulations. There should be no foreign objects on the table. Attention! Electricity! Isolation of conductors should not be broken. Do not turn on the chain without the permission of the teacher. Do not touch your hands to rotating parts of the electric motor. Long hair must be removed so that they do not get into the rotating parts of the engine. After performing the work, the workplace will put in order, the chain will break and disassemble.
The procedure for performing work. 1. Watch the model of the electric motor. Specify in Figure 1 the main parts of it. 1 2 3 Figure 1 4 5 1 - ______________________________ 2 - ______________________________ 3 - ______________________________________________________________________________________________________
2. Open the electrical circuit consisting of a current source, an electric motor model, key, connecting everything sequentially. Draw a chain diagram.
3. Give the engine to rotate. If the engine does not work, find the reasons and eliminate them. 4. Change the current direction in the chain. Watch the rotation of the moving part of the electric motor. 5. Business output.
Literature: 1. Physics. 8 cl.: Studies. For general education. Institutions / A.V.Pernyshkin.-4th ed., DRABOT.-M.: Drop, 2008. 2. Physics. 8 cl.: Studies. For general education. Institutions / N.S. Puryshev, N.E.Vazhevskaya. - 2nd ed., Stereotype - M.: Drop, 2008. 3. Laboratory work and control tasks in physics: notebook for students of the 8th grade.-Saratov: Lyceum, 2009. 4. Tetraffic for laboratory work. Sarakhman I.D. MOU SOSH No. 8 of Mozdok RSO-Alania. 5.Laboratory work in school and houses: Mechanics / V.F. Shelov.-M .: Enlightenment, 2007. 6. The collector of tasks in physics. 7-9 Classes: Pupils for students. Institutions / V.I. Lukashik, E.V. Ivanova. - 24th ed.-m.: Enlightenment, 2010.
Preview:
Laboratory work number 11
(on the model)
purpose of work
Instruments and materials
Progress.
Laboratory work number 11
Study of the Electric DC motor
(on the model)
purpose of work : Get acquainted on the DC motor model with its device and work.
Instruments and materials: Motor Model, Laboratory Power Supply, Key, Connecting Wires.
Safety regulations.
There should be no foreign objects on the table. Attention! Electricity! Isolation of conductors should not be broken. Do not turn on the chain without the permission of the teacher. Do not touch your hands to rotating parts of the electric motor.
Training tasks and questions
1. What physical phenomenon is the action of an electric motor?
2. What are the advantages of electrical engines compared to thermal?
3. Where is the DC electrical engines?
Progress.
1. Watch the model of the electric motor. Specify in Figure 1 the main parts of it.
2. Open the electrical circuit consisting of a current source, an electric motor model, key, connecting everything sequentially. Draw a chain diagram.
Fig.1
Take output.
3. Give the engine to rotate. If the engine does not work, find the reasons and eliminate them.
4. Change the current direction in the chain. Watch the rotation of the moving part of the electric motor.
Fig.1
current "Place of lesson in the work 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 DC motor.
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.
study the device, principle of operation, characteristics of the DC motor;
purchase practical start, operation, operation and stop of DC electric motor;
experimentally explore theoretical information on the characteristics of the DC electric motor.
The main theoretical provisions
DC motor is an electric machine intended for transforming electrical energy into mechanical.
The DC motor device does not have differences from the DC generator. This circumstance makes electric direct current machines reversible, that is, it allows them to be used both in the generator and in engine modes. Structurally, the DC motor has fixed and movable elements that are shown in Fig. one.
The fixed part is the stator 1 (bed) made of steel casting, consists of the main 2 and additional 3 poles with excitation windings 4 and 5 and brush traverse with brushes. The stator performs the function of the magnetic pipeline. With the help of the main poles, constant in time and the magnetic field is fixed in space. Additional poles are placed between the main poles and improve the switching conditions.
The movable part of the DC electric motor is the rotor 6 (anchor), which is placed on the rotating shaft. Anchor also plays the role of a magnetic pipeline. It is diagnosed from thin, electrically isolated from each other, thin sheets of electrical steel with an increased silicon content, which reduces power loss. In the grooves, the anchors pressed the windings 7, the findings of which are connected to the collector plates 8, placed on the same motor (see Fig. 1).
Consider the principle of operation of the DC electric motor. Connecting a constant voltage to the clamps of the electrical machine causes the simultaneous appearance in the excitation windings (stator) and in the current anchor windings (Fig. 2). As a result of the interaction of the current anchor with a magnetic stream, the created excitation winding in the stator arises f.determined by the AMPER's law . The direction of this force is determined by the rule of the left hand (Fig. 2), according to which it is oriented perpendicular to both to the current i.(in the anchor winding) and the vector of magnetic induction IN(created excitation winding). As a result, a pair of forces act on the rotor (Fig. 2). On the upper part of the rotor, the force acts to the right, on the bottom - left. This pair of strength creates a torque, under the action of which anchor is driven into rotation. The magnitude of the emerging electromagnetic moment turns out to be equal
M. = c. M. I. I F.,
where from M - coefficient depending on the design of the anchor winding and the number of electric motor poles; F.- the magnetic stream of one pair of the main poles of the electric motor; I. I - current anchor engine. As follows from fig. 2, the turn of the windings of the anchor is accompanied by simultaneous change in polarity on collective plates. The current direction in the turns of the winding of the anchor varies to the opposite, but the magnetic flux of the excitation windings retains the former direction, which causes the invariance of the direction of forces f.and therefore the rotational moment.
The rotation of the anchor in the magnetic field leads to the appearance of the EMF in its winding, the direction of which is determined by the rule of the right hand. As a result, for presented in Fig. 2 The configurations of the fields and forces in the anchor winding will arise an induction current directed opposite to the main current. Therefore, the emerging EMF is called anti-EDS. The magnitude of it is equal
E. = from E. nF,
where n.- frequency of rotation of the anchor of the electric motor; from E is a coefficient depending on the structural elements of the machine. This EMF worsens the operating characteristics of the electric motor.
The current anchor creates a magnetic field that affects the magnetic field of the main poles (stator), which is called an anchor reaction. In idling mode, the magnetic field is created only by the main poles. This field is symmetrically relative to the axes of these poles and coaxially with them. When connected to the load engine at the expense of the current in the anchor winding, a magnetic field is created - the anchor field. The axis of this field will be perpendicular to the axis of the main poles. Since when rotating anchor, the current distribution in the conductors of the anchor remains unchanged, the field of the anchor remains fixed in space. Addition of this field with a field of main poles gives a resulting field that unfolds at an angle against the direction of rotation of the anchor. As a result, the torque decreases, since part of the conductors falls into the zone of the pole of the opposite polarity and creates a braking point. In this case, the brushes and the overtaking of the collector occur, the longitudinal demagnetizing field occurs.
In order to reduce the effect of the anchor response, additional poles are embedded in it. The windings of such poles are included sequentially with the main winding of the anchor, but the change in the winding direction in them causes the appearance of a magnetic field directed against the magnetic field of the anchor.
To change the direction of rotation of the DC motor, it is necessary to change the polarity of the voltage, summing up to the anchor or the excitation winding.
Depending on the method of incorporating the excitation winding, DC electric motors with parallel, sequential and mixed excitation are distinguished.
In engines with parallel excitation, the winding is designed for the full voltage of the supply network and turns on parallel to the chain of the anchor (Fig. 3).
A sequential excitation engine has an excitation winding that is turned on consistently with an anchor, so this winding is calculated for a complete anchor current (Fig. 4).
Mixed excitation engines have two windings, one turns on in parallel, the other is sequentially with anchor (Fig. 5).
Fig. 3 Fig. four
When the DC electric motors start (regardless of the excitation method), there are significant launchers that can lead to their failure arise. This occurs as a result of the allocation of a significant amount of heat in the winding of the anchor and the subsequent disruption of its isolation. Therefore, the start of the DC motors is performed by special starting devices. In most cases, the simplest start-up device is used for these purposes - launcher. The process of starting the DC motor with a launcher is shown on the example of a DC motor with parallel excitation.
Based on the equation composed in accordance with the second law of Kirchoff for the left side of the electrical circuit (see Fig. 3), the launcher is fully removed ( R.start \u003d 0), Current anchor
,
where U.- voltage supplied to the electric motor; R. I am an anchor winding resistance.
In the initial moment of starting the electric motor, the speed of rotation of the anchor n.\u003d 0, therefore, the antielectro-moving force, inserted in the anchor winding, in accordance with the previously obtained expression will also be zero ( E.= 0).
Resistance to winding anchor R. I am a rather small value. In order to limit it possible at the same time, it is unacceptably the high current in the anchor chain when started, consistently with an anchor, regardless of the engine excitement method turns on the launcher (starting resistance R. start). In this case, the launcher of the anchor
.
Startup resistance R. Start counting for work only for starting time and chosen in such a way that the starting current of the anchor of the electric motor did not exceed the permissible value ( I. I started 2 I. I, number). As the EDC electric motor is accelerated, in the anchor winding, due to the increasing frequency of its rotation N increases ( E.=from E. nF). As a result of this, the anchor current will decrease in other places. In this case, the resistance of the launcher R. start As the electric motor anchor is overclocked, it is necessary to gradually reduce. After the end of the engine overclocking to the nominal value of the speed of rotation, the EDC anchor increases so much that the starting resistance can be reduced to zero, without the danger of significant increase in the anchor current.
Thus, starting resistance R. Start in the chain anchor is necessary only when starting. In the process of normal operation of the electric motor, it must be disconnected, firstly, because it is designed for short-term operation during start-up, secondly, in the presence of starting resistance, thermal loss of power will occur in it, equal R. start I. 2 I, significantly reduce the efficiency of the electric motor.
.
Taking into account the expression for EMF ( E.=from E. nF), writing the resulting formula relative to the frequency of rotation, we obtain the frequency equation (high-speed) characteristics of the electric motor n.(I. I):
.
It follows from it that in the absence of a load on the shaft and the current anchor I. I = 0 frequency of rotation of the electric motor with this value of the supply voltage
.
Rotation frequency of electric motor n. 0 it is the frequency of rotation of the perfect idling. In addition to the parameters of the electric motor, it also depends on the value of the supply voltage and magnetic flux. With a decrease in the magnetic flux, with other things being equal, the speed of rotation of the perfect idle stroke increases. Therefore, in the event of a cliff of the excitation winding chain, when the excitation current becomes zero ( I. B \u003d 0), the magnetic flux of the engine is reduced to the value equal to the value of the residual magnetic flux F. Ost. At the same time, the engine "goes to the spread", developing the speed of rotation, is much more nominal, which represents a certain danger both for the engine and for the service personnel.
Frequency (high-speed) characteristics of the DC motor with parallel excitation n.(I. I) with the constant value of the magnetic flux F.=const.and constant value of the supply voltage U \u003d Const.it has the form of direct (Fig. 6).
Expressing in equations of frequency characteristics of an anchor current through the electromagnetic moment of the engine M \u003dfrom M. I. I F., we obtain the equation of mechanical characteristics, i.e. dependence n.(M.) As U \u003d Const.for engines with parallel excitation:
.
Neglecting the effect of an anchor reaction in the process of changing the load, you can take the electromagnetic moment of the engine in proportional anchor current. Therefore, the mechanical characteristics of DC motors have the same form as the corresponding frequency characteristics. The electric motor with parallel excitation has a rigid mechanical characteristic (Fig. 7). From this characteristic, it can be seen that its rotational speed with an increase in the load moment is reduced slightly, since the excitation current with parallel turning on the excitation winding and, accordingly, the magnetic flux of the engine remains almost unchanged, and the resistance of the chain of the anchor is relatively small.
The operating characteristics of the DC electric motor with parallel excitation are shown in Fig. 8. From these characteristics it can be seen that the frequency of rotation n.electric motors with parallel excitation with an increase in the load decreases somewhat. The dependence of the useful torque on the motor shaft from power R 2 it is an almost straight line, since the moment of this engine is proportional to the load on the shaft: M.=kr 2 / n.. The curvature of this dependence is explained by some reduction in the frequency of rotation with an increase in the load.
For R 2 \u003d 0 Current consumed by the electric motor is equal to an idle current. With increasing power, the anchor current increases by approximately the same dependence as the load moment on the shaft, since provided F.=const.current anchor is proportional to the moment of load. The efficiency of the electric motor is determined as the ratio of useful power on the shaft to the power consumed from the network:
,
where R 2 - useful power on the shaft; R 1 =UI- power consumed by the electric motor from the power supply; R Ey \u003d. I. 2 I. R. I am electrical power losses in an anchor chain, R EV \u003d. UI in, \u003d. I. 2 B. R. in - electrical power loss in the excitation circuit; R fur - mechanical power loss; R M - power loss on hysteresis and vortex currents.
With a constant voltage of the supply network and a constant magnetic stream in the process of changing the resistance value of an anchor chain, a family of mechanical characteristics can be obtained, for example, for an electric motor with a parallel excitation (Fig. 9).
The advantage of the considered method of regulation lies in its relative simplicity and the possibility of obtaining a smooth change in the speed of rotation widely (from zero to the nominal value of the frequency n. number). The disadvantages of this method include the fact that there are significant power losses in the addition resistance increasing with a decrease in the speed of rotation, as well as the need to use additional regulating equipment. In addition, this method does not allow you to adjust the frequency of rotation of the electric motor up from its nominal value.
Changes to the rotation frequency of the DC motor can be achieved and as a result of changing the value of the magnetic flux of excitation. With a change in the magnetic flux in accordance with the frequency response equation for the DC motors with parallel excitation, with a constant value of the supply network voltage and the resistance of the anchor chain, the mechanical characteristics presented in Figure can be obtained. 10.
The disadvantages of this method include a relatively small range of regulation due to the presence of restrictions on the mechanical strength and switching of the electric motor. The advantage of this method of regulation is its simplicity. For engines with parallel excitation, this is achieved by changing the resistance of the adjustment R. r in the excitation circuit.
In direct current engines with a sequential excitation, the change in the magnetic flux is achieved by by shunting the excitation winding with the resistance having a corresponding value, or by closing the spice of a certain number of turns of the excitation winding.
Widespread use, especially in the electric drives built by the generator - engine, received a method for regulating the rotational speed by changing the voltage on the engine anchor clips. With a constant magnetic flow and resistance of an anchor chain as a result of a voltage change, a family of frequency characteristics can be obtained.
With the change in the supply voltage, the speed of rotation of the perfect idle n 0 In accordance with the previously reduced expression varies proportional to the voltage. Since the resistance of the chain of the anchor remains unchanged, the rigidity of the mechanical characteristics family does not differ from the rigidity of the natural mechanical characteristic when U.=U. nom.
The advantage of the considered method of regulation is a wide range of rotational speed changes without increasing power losses. The disadvantages of this method include the fact that the source of an adjustable supply voltage is needed, and this leads to increase the mass, dimensions and installation costs.
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 present the life of modern society based on high technologies, and something more efficient is not yet invented.
Synchronous principle of operation of the electric motor
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 the concepts for measuring the resistances of the anchor chain and excitation windings (Fig.6.4) and 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 of a small cross section with a large number of 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). Its graphic image is 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. It follows three possible ways to regulate engine speed:
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.
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