The stator of the alternator creates. How does an electric generator work?

All tips

The universe has provided humanity with a trillion ways to obtain electricity, each stage of development is characterized by its own technologies. Let's say that historically the Van de Graaff constant charge generator is considered the first. Wrong point of view. People used other varieties before. Today we will look at the device and operating principle of an alternating current generator. Let's get started.

Operation of electric current generators

The principle is intended to create a potential relative to the Earth, considered zero. Wrong, but everything in the world is relative. Although the earth's surface carries a charge, the potential difference between the generator terminals and the soil plays a role. An object standing on the ground is enveloped by the field of the planet, we consider the postulate to be true. The generator was the first to be invented direct current. More like tension. The voltage turned out to be fantastic, the device produced little current. The operating principle is simple:

Operating principle of the generator

The tape rubs, a charge is formed locally.
By means of a conveyor mechanism, the section reaches the current collector.
The density is equalized by the conductivity of the ball terminal.

As a result, the sphere acquires a charge with a density equal to the local ribbon. It is clear that such generators are not very convenient; in 1831, Michael Faraday created something new. Using a magnetized horse shoe, a rotating copper disk generated electricity in a different way: the phenomenon of magnetic induction. The current came out alternating. Consequently, the field ceased to be static, becoming electromagnetic. Let's explain:

In nature, charges of electricity of a positive or negative sign are often found; no one has been able to find the poles of a magnet separately.
An alternating electric field causes a corresponding response in the ether. Expressed by the production of an alternating magnetic component in a plane perpendicular to the original one.

The process continues continuously, called electromagnetic wave. Masters free space straight ahead until the energy fades. When it comes to wires, electricity travels relatively easily. But! While the cable is braided. The screen has disappeared, there is no grounding (grounding) - the wave begins to emit. The effect is exploited by wireless indicator screwdrivers, helping to identify (localize) sources of interference at an industrial frequency of 50 Hz. And if the computer system unit is not grounded, using this little thing you can easily fix the problem.

Helps test for harmful radiation from displays. The 50 Hz frequency is easily emitted by wires. This aspect increases the costs of power plants (losses) and harms the health of citizens. How is energy generated in a Faraday generator? School teachers explained: when the frame rotates in the field of a magnet, the induction through the area changes and is induced electricity.

Mechanical energy of movement is converted into electrical energy. Guessed it, humanity is exploiting:

Masses of water falling down from a dam.
Steam energy from thermal and nuclear power plants.

The two main mechanisms for obtaining energy. Electricity becomes the movement of a generator turbine blade. Nature has given birth to devices that burn diesel fuel and kerosene; the operating principle is not much different. The difference is limited by mobility, blade rotation speed.

Generation of urban electrical energy

Let's look at the design of a hydroelectric power generator. To accumulate the potential energy of the water moving the river bed, a dam is erected. The level upstream quickly begins to rise. To avoid a breakthrough (of any type), part of the multi-ton mass is released (in some places special sluices are installed to allow fish through for spawning). The useful part of the flow passes through the guide vane. Familiar with the device jet engines, understood the speech. The guide vane is the configuration of the valves; by changing the position, the amount of passing medium (water) is regulated.

They said in the reviews that there are strict requirements for the frequency of generated electricity. Scientists have calculated: it can be achieved at the current level of development by using massive blades that are not affected by small wave impacts. The average mass of passing water is taken into account, small jumps are concealed by the incredible mass of the propeller. Obviously, having significant dimensions, the rotation speed is powerless to reach 50 Hz (3000 rpm). The blade makes 1-2 rpm.

The screw rotates the generator rotor. A moving axis seated with field windings. Coils through which direct current is passed to create a stable magnetic field. There is no radiation, the voltage value is constant (see above). Implicit fluctuations are observed, the result is not reflected in the essence of the process: the shaft is formed by several rotating magnets.

A subtle point arises: how to obtain a frequency of 50 Hz. We quickly came to the conclusion: it is unprofitable to rectify alternating current and then install a reverse conversion inverter. Many wire coils (a frame from Faraday’s experiments) were placed along the stator, in which induction will be induced. Through proper switching, it is possible to remove the required 230 volts from the generator (in fact, there are also step-down transformers) with a frequency of 50 Hz. The generators produce three phases shifted by 120 degrees. A new question arises - to ensure stability. Apply a measured amount of water while the blade picks up speed? Almost impossible, proceed as follows:

In addition to current collection coils, the stator contains exciting coils.
A frequency voltage is supplied there, allowing the blade to reach the desired speed.
The result is actually a huge synchronous motor.

The initial acceleration is accelerated by the flow of water, the auxiliary voltage holds the propeller trying to exceed the set speed. The water actually pushes the machine, the excitation voltage will serve as regulation (of course, alternating current is supplied to the stator). Required to receive more power, the dam's guide apparatus opens slightly. The mass of water becomes more solid, it would certainly disrupt the momentum. It is necessary to increase the stator excitation current, the controlling field becomes stronger, the situation remains within normal limits.

Caterpillar internal combustion engine turning generator

The generator power increases. Is the voltage level maintained? According to Faraday's law of electromagnetic emf, voltage is determined by the rate of change of the magnetic field, the number of turns. It turns out that by constructively choosing the area of the coils and the length of the cable, we set the output voltage of the generator. Of course, everyone must have their own blade rotation speed. Maintained by rotor excitation current. As power increases, the emf increases. An increase in the excitation current increases the rate of change in the magnetic field strength.

We need a way to maintain the previous parameters. Variable ratio isolation transformers are often used. The consumer changes the current, the voltage remains constant. The parameters specified by the standards are ensured. The design of the alternating current generator is based on the excitation of the stator windings, the rest comes down to methods for regulating parameters.

Parameter adjustment of alternators

In the simplest case, power cannot be changed. In household (small generators) the circuit monitors the voltage and changes the value of the excitation current. Rarely does the situation benefit the consumer. Diesel fuel is being consumed. It turns out that the previous energy is wasted, some of it is dissipated by space. It’s not scary, when we return part of the river’s speed to the Earth, a rare miser will want to burn fuel for nothing.

Readers understood: the speed will drop if you do not reduce the supply of water, gas, steam - in general, the driving force. Monitors a separate regulatory circuit equipped with adjustment mechanisms. It is better for a private home to create a battery system; today it is possible to power lighting, laptops, and many other devices with 12 volts DC. The network can be equipped with a tap for periodic battery charging. As we remember, there are two methods:

With constant current. The voltage varies, one tenth of the capacity is charged every hour. The duration of the process is 600 minutes.
WITH constant voltage. The current drops exponentially and initially will be relatively large. The main drawback of the technique.

The operating principle of the alternator will allow you to recharge the batteries, guided by necessity. It is clear that a galvanic isolation circuit will be required before the battery cascade. You can guess from what you read that hydroelectric power plants use devices with an adjustable transformation ratio. Methods for implementing the idea can be different:

Transformers with switched windings have become widespread. The number of turns can be changed by switching circuits with contactors.
A smoother ratio provides sliding contact. Here the turns of one coil are stripped, the current collector runs back and forth, changing the number of working turns. It is clear that it is difficult to pass a large current, a spark will appear, and in the case of a hydroelectric power station it will become an arc. Rather, it is a device for regulating relatively low powers.

From the above it follows: it is logical to change the excitation current of the rotor of a hydroelectric power station in jumps in time with the switching of the windings of the control transformer. Then a smooth adjustment occurs, the voltage parameters return to normal. They explained in general terms how an alternator works. It is worth noting: the variety is not exhausted by design. The described type of devices forms the backbone of a family called synchronous alternating current generators. They provide cities, for the most part, with energy.

Asynchronous alternator

Asynchronous generators are characterized by the absence electrical communication between stator and rotor. The speed is controlled by a guide vane. As the frequency stability decreases, the voltage amplitude also becomes unstable. As a result, we can note the relative simplicity of the design of the asynchronous alternating current generator; the stability of the parameters does not shine with good indicators.

A distinctive feature is the ability of disadvantages asynchronous motors smoothly migrate, infecting new devices. Obviously, to supply consumers with energy, the frequency of the current is adjusted, the power is random. Although, if the generator is in a relatively constant environment, this will not be a big problem.

The term “generation” in electrical engineering comes from Latin. It means "birth". In relation to energy, we can say that generators are called technical devices engaged in electricity generation.

It should be noted that electric current can be produced by converting various types of energy, for example:

chemical;

light;

thermal and others.

Historically, generators are structures that convert rotational kinetic energy into electricity.

According to the type of electricity generated, generators are:

1. DC;

2. variable.

The physical laws that make it possible to create modern electrical installations for generating electricity through the transformation of mechanical energy were discovered by scientists Oersted and Faraday.

In the design of any generator, it is realized when electric current is induced in a closed frame due to its intersection with a rotating magnetic field, which is created in simplified models for domestic use or by excitation windings on industrial products of high power.

When the frame rotates, the magnitude of the magnetic flux changes.

The electromotive force induced in the coil depends on the rate of change of the magnetic flux passing through the frame in a closed loop S, and is directly proportional to its value. The faster the rotor rotates, the higher the voltage generated.

In order to create a closed circuit and drain electric current from it, it was necessary to create a collector and a brush assembly that ensures constant contact between the rotating frame and the stationary part of the circuit.

Due to the design of the spring-loaded brushes, which are pressed against the commutator plates, electric current is transmitted to the output terminals, and from them it then flows into the consumer network.

The principle of operation of the simplest DC generator

When the frame rotates around its axis, its left and right halves cyclically pass near the south or north pole of the magnets. In them, each time the directions of the currents change to the opposite so that at each pole they flow in one direction.

In order to create a direct current in the output circuit, a semi-ring is created on the collector node for each half of the winding. Brushes adjacent to the ring remove the potential of only their sign: positive or negative.

Since the half-ring of the rotating frame is open, moments are created in it when the current reaches maximum value or missing. In order to maintain not only the direction, but also a constant value of the generated voltage, the frame is made using specially prepared technology:

it uses not one turn, but several - depending on the value of the planned voltage;

the number of frames is not limited to one copy: they try to make them sufficient to optimally maintain voltage drops at the same level.

For a DC generator, the rotor windings are located in slots. This allows you to reduce losses of induced electromagnetic field.

Design features of DC generators

The main elements of the device are:

external power frame;

magnetic poles;

stator;

rotating rotor;

switching unit with brushes.

The body is made of steel alloys or cast iron to provide mechanical strength to the overall structure. Additional task the housing is the transmission of magnetic flux between the poles.

The magnet poles are attached to the housing with studs or bolts. A winding is mounted on them.

Stator, also called a yoke or core, is made of ferromagnetic materials. The excitation coil winding is placed on it. Stator core equipped with magnetic poles that form its magnetic force field.

Rotor has a synonym: anchor. Its magnetic core consists of laminated plates, which reduce the formation of eddy currents and increase efficiency. The grooves of the core contain the rotor and/or self-excitation windings.

Switching node with brushes may have a different number of poles, but it is always a multiple of two. The brush material is usually graphite. The collector plates are made of copper, as the most optimal metal suitable for the electrical properties of current conductivity.

Thanks to the use of a commutator, a pulsating signal is generated at the output terminals of the DC generator.

Main types of DC generator designs

Depending on the type of power supply to the excitation winding, devices are distinguished:

1. with self-excitation;

2. working on the basis of independent inclusion.

The first products can:

use permanent magnets;

or work from external sources, for example, batteries, wind power...

Generators with independent switching operate from their own winding, which can be connected:

sequentially;

shunts or parallel excitation.

One of the options for such a connection is shown in the diagram.

An example of a DC generator is a design that was previously often used in automotive applications. Its structure is the same as that of an asynchronous motor.

Such collector structures are capable of operating in engine or generator mode simultaneously. Due to this, they have become widespread in existing hybrid cars.

The process of formation of an anchor reaction

It occurs in idle mode when the brush pressing force is incorrectly adjusted, creating a non-optimal mode of their friction. This may result in reduced magnetic fields or a fire due to increased spark generation.

Ways to reduce it are:

compensation of magnetic fields by connecting additional poles;

adjusting the shift of the position of the commutator brushes.

Advantages of DC Generators

These include:

no losses due to hysteresis and the formation of eddy currents;

work in extreme conditions;

reduced weight and small dimensions.

The principle of operation of the simplest alternating current generator

Inside this design all the same parts are used as in the previous analogue:

a magnetic field;

rotating frame;

collector unit with brushes for current drainage.

The main difference lies in the design of the commutator unit, which is created in such a way that when the frame rotates through the brushes, contact is constantly created with its half of the frame without cyclically changing their position.

Due to this, the current, changing according to the laws of harmonics in each half, is transmitted completely unchanged to the brushes and then through them to the consumer circuit.

Naturally, the frame is created by winding not one turn, but a calculated number of turns to achieve optimal voltage.

Thus, the operating principle of direct and alternating current generators is common, and the design differences lie in manufacturing:

rotating rotor collector unit;

winding configurations on the rotor.

Design features of industrial alternating current generators

Let's consider the main parts of an industrial induction generator, in which the rotor receives rotational motion from a nearby turbine. The stator design includes an electromagnet (although the magnetic field can be created by a set of permanent magnets) and a rotor winding with a certain number of turns.

An electromotive force is induced inside each turn, which is sequentially added in each of them and forms at the output terminals the total value of the voltage supplied to the power circuit of the connected consumers.

To increase the amplitude of the EMF at the output of the generator, a special design of the magnetic system is used, made of two magnetic cores through the use of special grades of electrical steel in the form of laminated plates with grooves. Windings are mounted inside them.

The generator housing contains a stator core with slots to accommodate a winding that creates a magnetic field.

The rotor rotating on bearings also has a magnetic circuit with grooves, inside of which a winding is mounted that receives the induced emf. Typically, a horizontal direction is chosen to place the rotation axis, although there are generator designs with a vertical arrangement and a corresponding bearing design.

A gap is always created between the stator and the rotor, which is necessary to ensure rotation and avoid jamming. But, at the same time, there is a loss of magnetic induction energy. Therefore, they try to make it as minimal as possible, optimally taking into account both of these requirements.

The exciter, located on the same shaft as the rotor, is a direct current electric generator with relatively low power. Its purpose is to supply electricity to the windings of a power generator in a state of independent excitation.

Such exciters are most often used with the designs of turbine or hydraulic electric generators when creating the main or backup method excitement.

The picture of an industrial generator shows the location of commutator rings and brushes for collecting currents from the rotating rotor structure. During operation, this unit experiences constant mechanical and electrical loads. To overcome them, a complex structure is created, which during operation requires periodic inspections and preventive measures.

To reduce the operating costs created, another, alternative technology is used, which also uses the interaction between rotating electromagnetic fields. Only permanent or electric magnets are placed on the rotor, and the voltage is removed from a stationary winding.

When creating such a circuit, such a design can be called the term “alternator”. It is used in synchronous generators: high-frequency, automobile, on diesel locomotives and ships, installations of power stations for the production of electricity.

Features of synchronous generators

Operating principle

The name and distinctive feature of the action lies in the creation of a rigid connection between the frequency of the alternating electromotive force induced in the stator winding “f” and the rotation of the rotor.

A three-phase winding is mounted in the stator, and on the rotor there is an electromagnet with a core and an excitation winding, powered from DC circuits through a brush commutator assembly.

The rotor is driven into rotation by a source of mechanical energy - a drive motor - at the same speed. Its magnetic field makes the same movement.

Electromotive forces of equal magnitude, but shifted by 120 degrees in direction, are induced in the stator windings, creating a three-phase symmetrical system.

When connected to the ends of the windings of consumer circuits, the phase currents in the circuit begin to act, which form a magnetic field that rotates in the same way: synchronously.

The shape of the output signal of the induced EMF depends only on the distribution law of the magnetic induction vector inside the gap between the rotor poles and the stator plates. Therefore, they strive to create such a design when the magnitude of the induction changes according to a sinusoidal law.

When the gap has a constant characteristic, the magnetic induction vector inside the gap is created in the shape of a trapezoid, as shown in line graph 1.

If the shape of the edges at the poles is corrected to oblique with the gap changing to the maximum value, then a sinusoidal distribution shape can be achieved, as shown by line 2. This technique is used in practice.

Excitation circuits for synchronous generators

The magnetomotive force arising on the excitation winding “OB” of the rotor creates its magnetic field. For this purpose, there are different designs of DC exciters based on:

1. contact method;

2. contactless method.

In the first case, a separate generator is used, called exciter "B". Its excitation winding is powered by an additional generator according to the principle of parallel excitation, called the “PV” subexciter.

All rotors are placed on a common shaft. Due to this, they rotate exactly the same. Rheostats r1 and r2 serve to regulate currents in the exciter and subexciter circuits.

With a contactless method There are no rotor slip rings. Mounted directly on it three-phase winding pathogen. It rotates synchronously with the rotor and transmits electric direct current through a co-rotating rectifier directly to the exciter winding “B”.

The types of contactless circuit are:

1. self-excitation system from its own stator winding;

2. automated scheme.

With the first method the voltage from the stator windings is supplied to a step-down transformer, and then to a semiconductor rectifier “PP”, which generates direct current.

In this method, the initial excitation is created due to the phenomenon of residual magnetism.

An automatic scheme for creating self-excitation includes the use of:

voltage transformer TN;

automated excitation regulator AVR;

current transformer CT;

rectifier transformer VT;

thyristor converter TP;

BZ protection unit.

Features of asynchronous generators

The fundamental difference between these designs is the absence of a rigid connection between the rotor speed (nr) and the EMF induced in the winding (n). There is always a difference between them, which is called "slip". It is designated Latin letter“S” and is expressed by the formula S=(n-nr)/n.

When a load is connected to the generator, a braking torque is created to rotate the rotor. It affects the frequency of the generated EMF and creates negative slip.

The rotor structure of asynchronous generators is made:

short-circuited;

phase;

hollow.

Asynchronous generators can have:

1. independent excitation;

2. self-excitation.

In the first case, an external source of alternating voltage is used, and in the second, semiconductor converters or capacitors are used in the primary, secondary, or both types of circuits.

Thus, alternating and direct current generators have many common features in the principles of construction, but differ in the design of certain elements.

A generator is a device that produces a product, generates electricity, or creates electromagnetic, electrical, sound, light vibrations and impulses. Depending on their functions, they can be divided into types, which we will consider below.

DC generator

In order to understand the principle of operation of a direct current generator, you need to find out its main characteristics, namely the dependencies of the main quantities that determine the operation of the device in the applied excitation circuit.

The main quantity is voltage, which is affected by the rotation speed of the generator, current excitation and load.

The basic principle of operation of a direct current generator depends on the effect of the energy division on the magnetic flux of the main pole and, accordingly, on the voltage received from the collector while the position of the brushes on it remains unchanged. For devices equipped with additional poles, the elements are arranged in such a way that the current separation completely coincides with geometric neutrality. Due to this, it will shift along the line of rotation of the armature to the optimal commutation position, followed by securing the brush holders in this position.

Alternator

The operating principle of an alternating current generator is based on the conversion of mechanical energy into electricity due to the rotation of a wire coil in a created magnetic field. This device consists of a stationary magnet and a wire frame. Each of its ends is connected to each other using a slip ring that slides over an electrically conductive carbon brush. Due to this scheme, the electrical induced current begins to move to the inner slip ring at the moment when the half of the frame connected to it passes past the north pole of the magnet and, conversely, to the outer ring at the moment when the other part passes past the north pole.

The most economical method on which the principle of operation of an alternator is based is strong generation. This phenomenon is obtained by using one magnet, which rotates relative to several windings. If it is inserted into a coil of wire, it will begin to induce an electric current, thus causing the galvanometer needle to deviate away from the “0” position. After the magnet is removed from the ring, the current will change its direction, and the arrow of the device will begin to deviate in the other direction.

Car generator

Most often it can be found on the front of the engine, the main part of the work is to rotate the crankshaft. New cars boast a hybrid type, which also serves as a starter.

The principle of operation of a car generator is to turn on the ignition, during which the current moves through the slip rings and is directed to the alkaline unit, and then goes to rewind the excitation. As a result of this action, a magnetic field will be formed.

Together with the crankshaft, the rotor begins its work, which creates waves that penetrate the stator winding. Alternating current begins to appear at the rewind output. When the generator operates in self-excitation mode, the rotation speed increases to a certain value, then the alternating voltage in the rectifier unit begins to change to constant. Ultimately the device will provide consumers necessary electricity, and the battery - current.

The principle of operation of a car generator is to change the speed of the crankshaft or change the load, at which the voltage regulator is turned on; it controls the time when the excitation rewind is turned on. When external loads decrease or rotor rotation increases, the switching period of the field winding is significantly reduced. At the moment when the current increases so much that the generator stops coping, the battery starts working.

Modern cars have a warning light on the instrument panel, which notifies the driver of possible deviations in the generator.

Electric generator

The operating principle of an electric generator is to convert mechanical energy into an electric field. The main sources of such force can be water, steam, wind, and an internal combustion engine. The principle of operation of the generator is based on the joint interaction of the magnetic field and the conductor, namely, at the moment of rotation of the frame, magnetic induction lines begin to intersect it, and at this time an electromotive force appears. It causes current to flow through the frame using slip rings and flow into the external circuit.

Inventory Generators

Today it is becoming very popular inverter generator, the operating principle of which is to create an autonomous power source that produces high-quality electricity. Such devices are used as temporary, as well as permanent sources nutrition. Most often they are used in hospitals, schools and other institutions where even the slightest voltage surges should not be present. All this can be achieved using an inverter generator, the operating principle of which is based on constancy and follows the following scheme:

Generation of high frequency alternating current.
Thanks to the rectifier, the resulting current is converted into direct current.
Then an accumulation of current is formed in the batteries and the oscillations of electric waves are stabilized.
With the help of an inverter, direct energy is changed into alternating current of the desired voltage and frequency, and then supplied to the user.

Diesel generator

The operating principle of a diesel generator is to convert fuel energy into electricity, the main actions of which are as follows:

when fuel enters a diesel engine, it begins to burn, after which it is transformed from chemical into thermal energy;
thanks to the presence of a crank mechanism, thermal force is converted into mechanical force, this all happens in the crankshaft;
The resulting energy is converted into electrical energy with the help of a rotor, which is what is needed at the output.

Synchronous generator

The operating principle of a synchronous generator is based on the same purity of rotation of the magnetic field of the stator and rotor, which creates a magnetic field together with the poles, and it crosses the stator winding. In this unit, the rotor is a permanent electromagnet, the number of poles of which can start from 2 and above, but they must be a multiple of 2.

When the generator starts, the rotor creates a weak field, but after increasing speed, a greater force begins to appear in the field winding. The resulting voltage is supplied to the device through an automatic control unit and controls the output voltage due to changes in the magnetic field. The basic operating principle of the generator is high stability of the outgoing voltage, but the disadvantage is the significant possibility of current overloads. To add to the negative qualities, you can add the presence of a brush assembly, which is still in certain time will have to be maintained, and this of course entails additional financial costs.

Asynchronous generator

The principle of operation of the generator is to constantly be in braking mode with the rotor rotating ahead, but still in the same orientation as the magnetic field at the stator.

Depending on the type of winding used, the rotor can be phase or short-circuited. The rotating magnetic field created with the help of the auxiliary winding begins to induce it on the rotor, which rotates with it. The frequency and voltage at the output directly depends on the number of revolutions, since the magnetic field is not regulated and remains unchanged.

Electrochemical generator

There is also an electrochemical generator, the device and operating principle of which is to produce hydrogen from electrical energy in the car for its movement and powering all electrical appliances. This apparatus is chemical because it produces energy through the reaction of oxygen and hydrogen, which is used in a gaseous state to produce fuel.

Acoustic noise generator

The principle of operation of the acoustic interference generator is to protect organizations and individuals from eavesdropping on conversations and various types of events. They can be monitored through window glass, walls, ventilation systems, heating pipes, radio microphones, wired microphones and laser devices for capturing the received acoustic information from windows.

Therefore, companies very often use a generator to protect their confidential information, the device and operating principle of which is to tune the device to a given frequency, if it is known, or to a certain range. Then a universal interference is created in the form of a noise signal. For this purpose, the device itself contains a noise generator of the required power.

There are also generators that are in the noise range, thanks to which you can mask the useful sound signal. This kit includes a block that generates noise, as well as its amplification and acoustic emitters. The main disadvantage of using such devices is the interference that appears during negotiations. In order for the device to fully cope with its work, negotiations should be carried out for only 15 minutes.

Voltage regulator

The basic principle of operation of the voltage regulator is based on maintaining the energy of the on-board network in all operating modes with various changes in the frequency of rotation of the generator rotor, ambient temperature and electrical load. This device can also perform secondary functions, namely to protect parts of the generating set from possible emergency mode installation and overload, automatically connect the excitation winding circuit or alarm system to the on-board system emergency work devices.

All such devices work on the same principle. The voltage in the generator is determined by several factors - current strength, rotor speed and magnetic flux. The lower the load on the generator and the higher the rotation speed, the higher the voltage of the device will be. Due to the greater current in the excitation winding, the magnetic flux begins to increase, and with it the voltage in the generator, and after the current decreases, the voltage also becomes less.

Regardless of the manufacturer of such generators, they all normalize the voltage by changing the excitation current in the same way. As the voltage increases or decreases, the excitation current begins to increase or decrease and conduct the voltage within the required limits.

IN Everyday life the use of generators greatly helps a person in solving many emerging issues.

Induction alternating current generator. In induction alternators, mechanical energy is converted into electrical energy. An induction generator consists of two parts: a movable one, which is called a rotor, and a stationary one, which is called a stator. The operation of the generator is based on the phenomenon of electromagnetic induction. Induction generators have a relatively simple design and make it possible to obtain large currents at a sufficiently high voltage. There are many types of induction generators available today, but they all consist of the same basic parts. This is, firstly, an electromagnet or permanent magnet that creates a magnetic field, and, secondly, a winding consisting of turns connected in series, in which an alternating electromotive force is induced. Since the electromotive forces induced in series-connected turns add up, the amplitude of the electromotive force of induction in the winding is proportional to the number of turns in it.

Rice. 6.9

The number of field lines piercing each turn varies continuously from a maximum value when it is located across the field to zero when the field lines slide along the turn. As a result, when the coil rotates between the poles of the magnet, every half turn the direction of the current changes to the opposite, and an alternating current appears in the coil. Current is diverted into the external circuit using sliding contacts. For this purpose, slip rings are attached to the winding axis and attached to the ends of the winding. Fixed plates - brushes - are pressed against the rings and connect the winding with the external circuit (Fig. 6.9).

Let a coil of wire rotate in a uniform magnetic field with a constant angular velocity. The magnetic flux penetrating the coil changes according to the law, here S– coil area. According to Faraday's law, an electromotive force of induction is induced in the winding, which is defined as follows:

Where N– number of turns in the winding. Thus, the electromotive force of induction in the winding changes according to a sinusoidal law and is proportional to the number of turns in the winding and the rotation frequency.

In an experiment with a rotating winding, the stator is a magnet and contacts between which the winding is placed. In large industrial generators, an electromagnet, which is the rotor, rotates, while the windings, in which the electromotive force is induced, are placed in the slots of the stator and remain stationary. In thermal power plants, steam turbines are used to rotate the rotor. The turbines, in turn, are driven by jets of water vapor produced in huge steam boilers by burning coal or gas (thermal power plants) or by decaying matter (nuclear power plants). Hydroelectric power plants use water turbines to turn the rotor, which are rotated by water falling from a great height.

Electric generators play a vital role in the development of our technological civilization, since they allow us to receive energy in one place and use it in another. A steam engine, for example, can convert coal combustion energy into useful work, but this energy can only be used where a coal firebox and a steam boiler are installed. A power plant can be located very far from electricity consumers - and, nevertheless, supply factories, houses, etc. with it.

The story goes (most likely, this is just a beautiful fairy tale) that Faraday showed a prototype of an electric generator to John Peel, the British Chancellor of the Exchequer, and he asked the scientist: “Okay, Mr. Faraday, all this is very interesting, but what is the use of it all?”

“What's the point? – Faraday was allegedly surprised. “Do you know, sir, how much taxes this thing will bring to the treasury over time?!”

Transformer.

Transformer. Electromotive force powerful generators power plants are large, meanwhile practical use Electricity usually requires not very high voltages, but energy transmission, on the contrary, requires very high voltages.

To reduce losses due to heating of wires, it is necessary to reduce the current in the transmission line, and, therefore, to maintain power, increase the voltage. The voltage produced by the generators (usually around 20 kV) is increased to 75 kV, 500 kV and even 1.15 MV, depending on the length of the transmission line. By increasing the voltage from 20 to 500 kV, that is, by 25 times, line losses are reduced by 625 times.

The conversion of alternating current of a certain frequency, at which the voltage increases or decreases several times with virtually no loss of power, is carried out by an electromagnetic device that has no moving parts - an electrical transformer. Transformer is an important element of many electrical appliances and mechanisms. Charging device and toys railways, radios and televisions - transformers work everywhere, lowering or increasing the voltage. Among them there are both very tiny ones, no larger than a pea, and real colossi weighing hundreds of tons or more.

Rice. 6.10

The transformer consists of a magnetic core, which is a set of plates that are usually made of ferromagnetic material (Fig. 6.10). There are two windings on the magnetic circuit - primary and secondary. The one of the windings that is connected to an alternating voltage source is called primary, and the one to which the “load” is connected, that is, devices that consume electricity, is called secondary. The ferromagnet increases the number of magnetic field lines by approximately 10,000 times and localizes the flux of magnetic induction within itself, so that the transformer windings can be spatially separated and yet remain inductively coupled.

The operation of a transformer is based on the phenomena of mutual induction and self-induction. The induction between the primary and secondary winding is reciprocal, that is, the current flowing in the secondary winding induces an electromotive force in the primary, just as the primary winding induces an electromotive force in the secondary. Moreover, since the turns of the primary winding cover their own lines of force, an electromotive force of self-induction arises in them. The electromotive force of self-induction is also observed in the secondary winding.

Let the primary winding be connected to an alternating current source with electromotive force, therefore, an alternating current arises in it, creating an alternating magnetic flux in the magnetic core of the transformer ? , which is concentrated inside the magnetic core and penetrates all turns of the primary and secondary windings.

In the absence of an external load, the power released in the transformer is close to zero, that is, the current strength is close to zero. Let us apply Ohm's law to the primary circuit: the sum of the electromotive force of induction and voltage in the circuit is equal to the product of the current and the resistance. Assuming , we can write: therefore, , Where F– the flux permeating each turn of the primary coil. In an ideal transformer, all the lines of force pass through all the turns of both windings, and since the changing magnetic field produces the same electromotive force in each turn, the total electromotive force induced in the winding is proportional to the total number of its turns. Hence, .

The voltage transformation ratio is equal to the ratio of the voltage in the secondary circuit to the voltage in the primary circuit. For the amplitude values of voltages on the windings, we can write:

Thus, the transformation ratio is defined as the ratio of the number of turns of the secondary winding to the number of turns of the primary winding. If the coefficient is , the transformer will be a step-up transformer, and if it is a step-down transformer.

The relations written above, strictly speaking, are applicable only to an ideal transformer in which there is no magnetic flux dissipation and no energy loss due to Joule heat. These losses may be due to the presence active resistance the windings themselves and the occurrence of induction currents (Foucault currents) in the core.

Toki Fuko.

Toki Fuko. Induction currents can also arise in solid massive conductors. In this case, a closed circuit of induction current is formed in the thickness of the conductor itself when it moves in a magnetic field or under the influence of an alternating magnetic field. These currents are named after the French physicist J.B.L. Foucault, who in 1855 discovered the heating of ferromagnetic cores electric machines and other metallic bodies in an alternating magnetic field and explained this effect by the excitation of induced currents. These currents are now called eddy currents or Foucault currents.

If the iron core is in an alternating magnetic field, then internal eddy currents are induced in it under the influence of an induction electric field - Foucault currents, leading to its heating. Since the electromotive force of induction is always proportional to the oscillation frequency of the magnetic field, and the resistance of massive conductors is small, at high frequencies in the conductors it will be released, according to the Joule-Lenz law, a large number of heat.

In many cases, Foucault currents are undesirable, so special measures must be taken to reduce them. In particular, these currents cause heating of the ferromagnetic cores of transformers and metal parts of electrical machines. To reduce losses of electrical energy due to the occurrence of eddy currents, transformer cores are made not from a solid piece of ferromagnet, but from individual metal plates isolated from each other by a dielectric layer.

Rice. 6.11

Eddy currents are widely used for melting metals in so-called induction furnaces (Fig. 6.11), for heating and melting metal workpieces, and producing especially pure alloys and metal compounds. To do this, the metal workpiece is placed in an induction furnace (a solenoid through which alternating current is passed). Then, according to the law of electromagnetic induction, induction currents arise inside the metal, which heat the metal and can melt it. By creating a vacuum in the furnace and using levitation heating (in this case, the forces of the electromagnetic field not only heat the metal, but also keep it suspended out of contact with the surface of the chamber), especially pure metals and alloys are obtained.

A generator is one of the main elements of a car’s electrical equipment, providing simultaneous power to consumers and recharging the battery.

The principle of operation of the device is based on the conversion of mechanical energy that comes from the motor into voltage.

In combination with a voltage regulator, the unit is called a generator set.

Modern cars are equipped with an alternating current unit that fully satisfies all stated requirements.

Generator device

The elements of the alternating current source are hidden in one housing, which also forms the basis for the stator winding.

In the manufacturing process of the casing, light alloys are used (most often aluminum and duralumin), and for cooling, holes are provided to ensure timely removal of heat from the winding.

There are bearings in the front and rear parts of the casing, to which the rotor is attached - main element power supply.

Almost all elements of the device fit in the casing. In this case, the housing itself consists of two covers located on the left and right sides - near the drive shaft and control rings, respectively.

The two covers are connected to each other using special bolts made of aluminum alloy. This metal is lightweight and has the ability to dissipate heat.

An equally important role is played by the brush assembly, which transmits voltage to the slip rings and ensures the operation of the assembly.

The product consists of a pair of graphite brushes, two springs and a brush holder.

We will also pay attention to the elements located inside the casing:

What are the requirements for a car generator?

There are a number of requirements for a car generator set:

The voltage at the output of the device and, accordingly, in the on-board network must be maintained at certain range, regardless of load or crankshaft speed.
The output parameters must be such that in any operating mode of the machine the battery receives sufficient charge voltage.

At the same time, every car owner must Special attention pay attention to the level and stability of the output voltage. This requirement is due to the fact that the battery is sensitive to such changes.

For example, if the voltage drops below normal, the battery is not charged to the required level. As a result, problems may occur during the process of starting the engine.

In the opposite situation, when the installation produces increased voltage, the battery is overcharged and breaks down faster.

The principle of operation of a car generator, circuit features

The operating principle of the generator unit is based on the effect of electromagnetic induction.

If a magnetic flux passes through the coil and changes, a voltage appears and changes at the terminals (depending on the rate of flux change). The reverse process works in a similar way.

So, to obtain magnetic flux, voltage must be applied to the coil.

It turns out that to create an alternating voltage, two components are required:

Coil (it is from it that the voltage is removed).
Magnetic field source.

An equally important element, as noted above, is the rotor, which acts as a source of the magnetic field.

The pole system of the node has a residual magnetic flux (even in the absence of current in the winding).

This parameter is small, so it can cause self-excitation only at high speeds. For this reason, a small current is first passed through the rotor winding, which ensures magnetization of the device.

The chain mentioned above involves the passage of current from the battery through the control lamp.

The main parameter here is the current strength, which should be within normal limits. If the current is too high, the battery will quickly discharge, and if it is too low, the risk of excitation of the generator at idle speed will increase.

Taking these parameters into account, the power of the light bulb is selected, which should be 2-3 W.

As soon as the voltage reaches the required parameter, the light goes out, and the excitation windings are powered by the car generator itself. In this case, the power source goes into self-excitation mode.

Voltage is removed from the stator winding, which is made in a three-phase design.

The unit consists of 3 individual (phase) windings wound according to a certain principle on a magnetic core.

The currents and voltages in the windings are shifted by 120 degrees. At the same time, the windings themselves can be assembled in two versions - “star” or “triangle”.

If the “triangle” circuit is selected, the phase currents in 3 windings will be 1.73 times less than total current, given by the generator set.

That is why in high-power automobile generators the “triangle” circuit is most often used.

This is precisely explained by lower currents, thanks to which it is possible to wind the winding with a wire of a smaller cross-section.

The same wire can also be used in star connections.

To ensure that the created magnetic flux goes to its intended purpose and is directed to the stator winding, the coils are located in special grooves in the magnetic core.

Due to the appearance of a magnetic field in the windings and in the stator magnetic circuit, eddy currents appear.

The action of the latter leads to heating of the stator and a decrease in generator power. To reduce this effect, steel plates are used in the manufacture of the magnetic circuit.

The generated voltage is supplied to the on-board network through a group of diodes (rectifier bridge), which was mentioned above.

After opening, the diodes do not create resistance and allow current to pass unhindered into the on-board network.

But with reverse voltage I is not passed through. In fact, only the positive half-wave remains.

Some car manufacturers replace diodes with zener diodes to protect electronics.

The main feature of the parts is the ability not to pass current up to a certain voltage parameter (25-30 Volts).

After passing this limit, the zener diode “breaks through” and passes reverse current. In this case, the voltage on the “positive” wire of the generator remains unchanged, which does not pose any risks to the device.

By the way, the ability of a zener diode to maintain a constant U at the terminals even after a “breakdown” is used in regulators.

As a result, after passing diode bridge(zener diodes) the voltage is rectified and becomes constant.

For many types of generator sets, the excitation winding has its own rectifier, assembled from 3 diodes.

Thanks to this connection, the flow of discharge current from the battery is excluded.

The diodes associated with the field winding operate on a similar principle and supply the winding with a constant voltage.

Here the rectifier device consists of six diodes, three of which are negative.

During operation of the generator, the excitation current is lower than the parameter supplied by the car generator.

Consequently, to rectify the current on the excitation winding, diodes with a rated current of up to two Amperes are sufficient.

For comparison, power rectifiers have a rated current of up to 20-25 Amperes. If it is necessary to increase the generator power, another arm with diodes is installed.

Operating modes

To understand the operating features of a car generator, it is important to understand the features of each mode:

When starting the engine, the main consumer of electrical energy is the starter. A feature of the mode is the creation of increased load, which leads to a decrease in the voltage at the battery output. As a result, consumers draw current only from the battery. That is why in this mode the battery is discharged with the greatest activity.
After starting the engine, the car generator switches to power source mode. From this moment on, the device provides the current necessary to power the load in the car and recharge the battery. As soon as the battery reaches the required capacity, the charging current level decreases. In this case, the generator continues to play the role of the main power source.
After connecting a powerful load, for example, air conditioning, interior heating, etc., the rotor rotation speed slows down. In this case, the car generator is no longer able to cover the current needs of the car. Part of the load is transferred to the battery, which operates in parallel with the power source and begins to gradually discharge.

Voltage regulator - functions, types, warning lamp

The key element of the generator set is the voltage regulator - a device that maintains a safe level of U at the stator output.

There are two types of such products:

Hybrid - regulators, the electrical circuit of which includes both electronic devices, and radio components.
Integrated - devices based on thin-film microelectronic technology. In modern cars, this option is most widespread.

An equally important element is the control lamp mounted on dashboard, from which we can conclude that there are problems with the regulator.

The ignition of the light bulb at the moment of starting the engine should be short-term. If it lights up constantly (when the generator set is in operation), this indicates a breakdown of the regulator or the unit itself, as well as the need for repair.

Subtleties of fastening

The generator set is fixed using a special bracket and bolted connection.

The unit itself is attached to the front of the engine, thanks to special paws and eyes.

If a car generator has special paws, the latter are located on the engine covers.

If only one fixing paw is used, the latter is placed only on the front cover.

In the paw installed in the rear part, as a rule, there is a hole with a spacer bushing installed in it.

The task of the latter is to eliminate the gap created between the stop and the fastening.

Audi A8 generator mounting.

And so the unit is mounted on a VAZ 21124.

Generator malfunctions and ways to eliminate them

The electrical equipment of a car tends to break down. In this case, the greatest problems arise with the battery and generator.

In the event of failure of any of these elements, operation of the vehicle in normal mode work becomes impossible or the car becomes completely immobilized.

All generator breakdowns are divided into two categories:

Mechanical. In this case, problems arise with the integrity of the housing, springs, belt drive and other elements that are not related to the electrical component.
Electrical. These include malfunctions of the diode bridge, wear of the brushes, short circuits in the windings, breakdowns of the regulator relay, and others.

Now let's look at the list of faults and symptoms in more detail.

1. There is insufficient charging current at the output:

2. Second situation.

When a car alternator produces the required level of current, but the battery still does not charge.

The reasons may be different:

Poor quality of drawing the ground contact between the regulator and the main unit. In this case, check the quality of the contact connection.
Voltage relay failure - check and replace it.
If the brushes are worn out or stuck, replace them or clean them from dirt.
The regulator's protective relay has tripped due to a short to ground. The solution is to find the location of the damage and fix the problem.
Other reasons are oily contacts, breakdown of the voltage regulator, short circuit in the stator windings, poor belt tension.

3. The generator works, but makes a lot of noise.

Possible malfunctions:

Short circuit between stator turns.
Wear of the bearing seat.
Loosening the pulley nut.
Bearing failure.

Repairing a car generator should always begin with an accurate diagnosis of the problem, after which the cause is eliminated through preventive measures or replacing the failed unit.

Operating practice shows that changing a car alternator is not difficult, but to solve the problem you must follow a number of rules:

The new device must have similar current-speed parameters as the factory unit.
Energy indicators must be identical.
The gear ratios of the old and new power sources must match.
The unit being installed must be suitable in size and easily attached to the motor.
The circuits of the new and old car generator must be the same.

Please note that devices mounted on foreign-made cars are fixed differently than domestic ones, for example, like on a TOYOTA COROLLA generator
and Lada Granta
.

Therefore, if you replace a foreign unit with a domestic product, you will have to install a new mount.

To conclude the story about car generators, it is worth highlighting a number of tips on what car owners should and should not do during operation.

The main point is installation, during which it is important to approach the polarity connection with utmost attention.

If you make a mistake in this matter, the rectifier device will break and the risk of fire increases.

Starting the engine with incorrectly connected wires poses a similar danger.

To avoid problems during operation, you should adhere to a number of rules:

Keep the contacts clean and monitor the serviceability of the vehicle's electrical wiring. Pay special attention to the reliability of the connection. If bad contact wires are used, the on-board voltage level will exceed the permissible limit.
Monitor the generator tension. If the tension is weak, the power supply will not be able to perform its intended tasks. If you tighten the belt, this can lead to rapid wear of the bearings.
Discard the wires from the generator and battery when performing electrical welding work.
If the warning light comes on and remains on after starting the engine, find out and eliminate the cause.

Special attention should be paid to the relay regulator, as well as checking the voltage at the output of the power source. In charging mode, this parameter should be at the level of 13.9-14.5 Volts.

In addition, from time to time check the wear and adequacy of the force of the generator brushes, the condition of the bearings and slip rings.

The height of the brushes should be measured with the holder removed. If the latter is worn down to 8-10 mm, replacement is required.

As for the force of the springs holding the brushes, it should be at the level of 4.2 N (for VAZ). At the same time, inspect the slip rings - there should be no traces of oil on them.

Also, the car owner must remember a number of prohibitions, namely:

Do not leave the car with the battery connected if there is a suspicion of a breakdown of the diode bridge. Otherwise, the battery will quickly discharge and the risk of a wiring fire increases.
Do not check the correct operation of the generator by jumping its terminals or disconnecting the battery while the engine is running. In this case, damage to electronic components may occur, on-board computer or voltage regulator.
Do not allow technical liquids to come into contact with the generator.
Do not leave the unit switched on if the battery terminals have been removed. Otherwise, this may lead to damage to the voltage regulator and electrical equipment of the car.
Conduct in a timely manner.

Knowing the operating features of the generator, the nuances of its design, the main malfunctions and subtleties of repair, you can avoid many problems with wiring and batteries.

Remember that the generator is a complex unit that requires special approach for use.

It is important to constantly monitor it, timely carry out preventive measures and replace parts (if necessary).

With this approach, the power source and the car itself will last a very long time.

If there is a video in the article and it does not play, select any word with the mouse, press Ctrl+Enter, enter any word in the window that appears and click "SEND". Thank you.