In 1832, an unknown inventor created the first single-phase synchronous multi-pole alternator. But in the very first electronic devices, only direct current was used, while alternating current could not find its practical application for a long time. However, they soon found out that it is much more practical to use not direct, but alternating current, that is, the current that periodically changes its value and direction. The advantages of alternating current are that it is more convenient to generate it using power plants, alternators are more economical and easier to maintain than analogs operating on direct current. Therefore, reliable AC electric motors were assembled, which immediately found their widespread use in industrial and domestic spheres. It should be noted that thanks to the existence of alternating current, its special physical phenomena, such inventions as radio, tape recorder and other automation and electrical engineering, without which it is difficult to imagine modern life, could appear.
Alternator device
An alternator is a device that converts mechanical energy into electrical energy.
It consists of a stationary part called a stator or armature (see figure) and a rotating part - a rotor or inductor. In an alternator, the rotor is an electromagnet that provides a magnetic field that is transmitted to the stator. On the inner surface of the stator there are axial cavities, the so-called grooves, in which the alternating current winding (conductor) is located. The generator stator is made of 0.35 mm pressed steel sheets, which are insulated with a varnished foil. These sheets are installed in the machine bed. The rotor is mounted inside the stator and rotated by the motor. The shaft is one of the parts for transmitting torque under the action of the supports located on it. On a common shaft with a generator, a so-called DC exciter is located, which supplies direct current to the rotor windings. The battery in the alternator acts as a starter battery, which has the ability to accumulate and store electricity when there is a shortage in the absence of engine operation and when there is a shortage of power, which the generator develops.
Application of alternators in life
During the past years, the popularity of the use of power plants and alternators has increased significantly. They are used in both industrial and domestic spheres. are the best option for use in manufacturing, hospitals, schools, shops, offices, business centers, as well as on construction sites, greatly simplifying construction in areas where electrification is completely absent. Household generators, more practical, compact and ideal for use in a cottage and a country house. Alternators are widely used in various fields and areas due to the fact that they can solve many important problems associated with the unstable operation of electricity or its complete absence.
Service
Almost any diesel power plant, regardless of its capacity and manufacturer, has 2 main components. It is an alternator and an internal combustion engine. Since it is necessary to maintain these units in working order, during their operation, a certain list of mandatory maintenance work is needed. Unfortunately, the overwhelming majority of owners believe that it is possible to limit themselves only to the timely replacement of the oil and filter, while "maintenance" can be carried out independently. But this often results in a complete failure of the device. As a result, it is not difficult to conclude that it is easier and cheaper to entrust the equipment to professionals who, thanks to their knowledge and vast experience, will be able to increase the service life of the diesel generator set and reduce costs in emergency situations.
Alternating current is the driving force of many industries and transport, in particular, cars. There are both small fist-sized models and giant devices several meters high.
A generator is the same technical system that converts mechanical (kinetic) energy into electrical energy. How does the generator work?
No matter how the generator is arranged, its action is based on the process electromagnetic induction- the appearance in a closed circuit of an electric current under the influence of a modified magnetic flux.
The generator is conventionally divided into 2 parts: an inductor and an armature.
The inductor is the part of the device where the magnetic field is created, and the armature is the half where the electromotive force or current is generated.
Its technical structure remains constant: a wire winding and a magnet.
An electromotive force is generated in the winding under the influence of a magnetic field. This is the basis for the generator. But a powerful alternating current cannot be obtained from such a primitive design. The conversion requires a strong magnetic flux.
For this, 2 steel cores are added to the wire winding, which determine the purpose and structure of the alternator. These are the stator and the rotor. The winding that creates the magnetic field is placed in the groove of one core - this is the stator, or inductor. It remains stationary, unlike the rotor. The stator is supplied with direct current. They are bipolar or multipolar.
The rotor, or also the armature, actively rotates with the help of bearings and produces an electromotive force or alternating current. It has an inner core with copper wire wound.
The generator has a robust metal housing with multiple outputs, depending on the intended use of the device. The number of wire-wound spools is changeable.
We understand the features of the operation of the unit
Now let's find out on what principle the operation of alternators is based. The operation scheme is quite simple and straightforward. Given a constant rotor speed, the electric current will be produced in a single stream.
The rotation of the rotor provokes a change in the magnetic flux. In turn, the electric field generates the appearance of an electric current. Through the contacts with rings at the end, the current from the rotor passes into the electrical circuit of the device. The rings have good sliding properties. They are firmly in contact with the brushes, which are permanent, stationary conductors between the electrical circuit and the copper wire winding of the rotor.
There is a current in the copper winding around the magnet, but it is very weak compared to the strength of the electric current that flows from the rotor through the circuit to the device.
For this reason, only a weak current applied to the slip contacts is used to rotate the rotor.
When assembling an alternator, it is very important to maintain the proportions of the parts, the size, the size of the gaps, the thickness of the wire strands.
You can assemble an alternator if you have all the necessary parts and a sufficient amount of copper wire in your home. It is quite possible to make a small unit. Or there are detailed instructions for use.
The device and principle of operation of the alternator in the video
An automobile generator, which is by all means part of the equipment of any vehicle, can be compared with the role of a power plant in supplying energy to the needs of the national economy.
It is the main (when the engine is running) source of electricity in the car and is designed to maintain a given and stabilized voltage of the car's electrical network through electrical wires that entangle the entire car from the inside. The principle of operation of an automobile generator is based on the theoretical representation of the operation of a classical electric generator, which transforms non-electrical forms of energy into electrical energy.
In the specific case of an automobile generator, electrical energy is generated by transforming the mechanical rotational motion of the crankshaft of the engine unit.
General working principle
The theoretical premises underlying the operation of electric generators are based on the well-known case of electromagnetic induction, which transforms one type of energy (mechanical) into another (electrical). The effect of this effect is manifested when copper wires are placed, laid in the form of a coil, and placed in a magnetic field of variable magnitude.
This contributes to the appearance of an electromotive force in the wires, which sets the electrons in motion. This movement of electric particles generates in, and on the terminal contacts of the wires, an electric voltage arises, the level directly dependent on the speed with which the magnetic field changes. The AC voltage generated in this way must be supplied to an external network.
In a car generator, to create a magnetic phenomenon, the stator windings are used, in which the rotor armature rotates under the influence of the field. Conductive windings are placed on the armature shaft, connected to special contacts in the form of rings. These ring contacts are also fixed to the shaft and rotate with it. With the help of conductive brushes, electrical voltage is removed from the rings and the generated energy is supplied to the electrical consumers of the vehicle.
The generator is started by means of a drive belt from the friction wheel of the crankshaft of the engine unit, which is started from a battery source to start work. To ensure effective transformation of the generated energy, the diameter of the generator pulley must be noticeably smaller in diameter than the friction wheel of the crankshaft. This allows for higher shaft speeds of the generating set. Under these conditions, it functions with an increase in its efficiency and provides increased current characteristics.
Requirements
To ensure safe operation in a given range of characteristics of the entire complex of electrical devices, the operation of an automobile generator must meet high technical parameters and guarantee the generation of a voltage level that is stable over time.
The main requirement for car generators is a stable current generation with the required power characteristics. These parameters are designed to provide:
- recharging;
- simultaneous operation of all involved electrical equipment;
- stable voltage of the power grid in a wide range of changes in the rotor shaft speed and dynamically connected loads;
In addition to the above parameters, the generator is designed taking into account its operation under critical loads and must have a strong case, at the same time have a low weight and acceptable overall dimensions, and have a low and acceptable level of industrial radio interference.
The device and design of an automobile generator
Fastening
The vehicle's alternator can be easily found in the engine compartment by lifting the bonnet. There it is secured with bolts and special corners to the front of the engine. The mounting feet and the tensioning lug of the device are located on the generator body.
Frame
Almost all units of the unit are installed in the generator housing box. It is manufactured using light alloy metals based on aluminum, which is excellent for the heat dissipation task. The body structure is a combination of two main parts:
- front cover from the side of slip rings;
- end caps on the drive side;
Brushes, voltage regulator and rectifier bridge are fixed on the front cover. The lids are combined into a single body structure by means of special bolts.
The inner surfaces of the covers fix the outer surface of the stator, securing its position. Also important structural units of the housing structure are the front and rear bearings, which provide the proper conditions for the operation of the rotor and fix it on the cover.
Rotor
The design of the rotor assembly consists of an electromagnet circuit with an excitation winding mounted on a carrier shaft. The shaft itself is made of alloy steel supplemented with lead additives.
Copper slip rings and special spring-loaded brush contacts are also attached to the rotor shaft. Slip rings are responsible for supplying current to the rotor.
Stator
The stator assembly is a structure consisting of a core with numerous slots (in most cases, their number is 36), in which the turns of three windings are laid, having an electrical contact with each other, either according to the "star" or "triangle" scheme. The core, also referred to as a magnetic circuit, is made in the form of a hollow spherical circle of metal plates pulled together by rivets or welded into a single monolithic block.
To increase the level of the magnetic field on the stator windings during the production of these plates, transformer iron with enhanced magnetic parameters is used.
Voltage regulator
This electronic unit is designed to compensate for the instability of rotation of the rotor shaft, which is connected to the crankshaft of the power unit of a car operating over a wide range of changes in the number of revolutions. The voltage regulator is connected to graphite current collectors and helps to stabilize a given constant output voltage supplied to the machine's electrical network. Thus, he guarantees the smooth operation of electrical equipment.
By their design solution, the regulators are divided into two groups:
- discrete;
- integral;
The first type includes electronic blocks, on the structural board of which radioelements are mounted, developed using discrete (case) technology, which is notable for the non-optimal density of the elements' arrangement.
The second type includes the majority of modern electronic voltage control units, developed taking into account the integral method of assembling radioelements made on the basis of thin-film microelectronic technology.
Rectifier
Due to the fact that constant voltage is required for the correct functioning of on-board instruments, the generator output supplies the vehicle's network through an electronic unit assembled on powerful rectifier diodes.
This 3-phase rectifier, consisting of six semiconductor diodes, three of which are connected to the negative terminal ("mass"), and the other three are connected to the positive terminal of the generator, is designed to transform AC voltage into DC voltage. Physically, the rectifier unit consists of a horseshoe-shaped metal heat sink with rectifier diodes placed on it.
Brush assembly
This assembly has the appearance of a plastic construction and is designed to transfer voltage to slip rings. It contains several elements inside the body, the main of which are spring-loaded brush sliding contacts. They come in two modifications:
- electrographite;
- copper-graphite (more wear-resistant).
Structurally, the brush assembly is often made in one unit with a voltage regulator.
Cooling system
The removal of excess heat that forms inside the generator housing is provided by fans mounted on its rotor shaft. Generators, in which the brushes, voltage regulator and rectifier unit are placed outside, outside its housing and protected by a special casing, take in fresh air through special cooling slots in it.
Generator external cooling impeller The device of classical design, with the placement of the above-mentioned units inside the generator case, provides a fresh air flow from the side of the slip rings.
Modes of operation
To understand the principle of operation of a car generator, it is necessary to present the modes of its operation.
- the initial period of starting the engine;
- operating mode of the engine.
At the initial moment of starting the engine, the main and only consumer consuming electrical energy is the starter. The generator is not yet involved in the process of generating energy, and the supply of electricity at this moment provides only the battery. Due to the fact that the strength of the consumed current with this scheme is very high and can reach hundreds of amperes, intensively consume the previously stored electrical energy.
Once the starting process is complete, the engine returns to operating mode, and the generator becomes a full-fledged power supplier. It generates the current necessary for the functioning of various electrical equipment that is connected to work. Together with this function, the alternator charges the battery while the engine is running.
After the accumulator has set what is necessary, the need for recharging decreases, the current consumption drops noticeably, and the generator continues to support the operation of only electrical equipment. As other resource-intensive consumers of electricity are connected to work, the generator's power at certain points in time may not be enough to provide the total load, and then the battery is included in the overall operation, the operation of which in this mode is characterized by a rapid loss of charge.
Conclusion
The car generator is designed and designed to supply power to standard electrical appliances and convert the mechanical energy of the crankshaft of the power unit into electrical energy.
The generator is located under the hood on the front of the engine. The design of the generator contains the main units - the body, stator, rotor, bearings, voltage regulator, rectifier bridge, brush unit and fans.
Diagnostics of an alternating current generator set using USB Autoscope III (Postalovsky oscilloscope).
GOAL OF THE WORK: Checking the functionality of the generating set.
1. Study of the basic diagram of the generator;
2. Studying the stages of preparing the device for operation;
3. Study of the order of work of diagnostics:
4. Checking the functionality of the generating set.
Purpose, device and principle of operation of the generator.
The generator set is designed to provide power to the consumers included in the electrical equipment system and to charge the battery while the car engine is running. The output parameters of the generator must be such that in any modes of vehicle movement, a progressive discharge of the battery does not occur. In addition, the voltage in the vehicle's on-board network supplied by the generator set must be stable over a wide range of speed and load changes.
The generator set is a fairly reliable device that can withstand increased engine vibrations, high engine compartment temperatures, exposure to a damp environment, dirt and other factors.
Alternators are installed on modern cars. For normal operation of the current consumers on the car, there must be a stable supply voltage, therefore, regardless of the generator rotor speed and the number of connected consumers, the generator voltage must be constant. Maintaining a constant voltage and protecting the generator from overload is provided by a device called voltage regulators or relay-regulators.
Depending on the road and climatic conditions and operating modes of vehicles, the voltage of the generator supplying consumers designed for a nominal voltage of 12 V should be within 13.2. 15.5 V.
The alternator is three-phase, synchronous, with electromagnetic excitation; in comparison with the direct current generator, it has a lower metal consumption and overall dimensions. With the same power, it is simpler in design and has a longer service life. A generator is called a synchronous generator because the frequency of the current it produces is proportional to the rotational speed of the rotor of the generator. Specific power of the alternator, i.e. the power of the generator per unit of its mass is approximately 2 times greater than that of the direct current generator. This makes it possible to increase the gear ratio of the generator drive by 2-3 times, as a result of which, at the engine idling speed, the alternators develop up to 40% of the rated power, which provides better conditions for charging the batteries and, as a result, increasing their service life. Along with this, alternators, despite their difference in series numbers, are unified for many models of cars and trucks, respectively, and have a number of interchangeable parts (drive pulleys, impellers, bearings, etc.), and have no fundamental differences in design.
The principle of operation of the generator.
The generator is based on the effect of electromagnetic induction. If a coil, for example, made of a copper wire, is penetrated by a magnetic flux, then when it changes, an alternating electric voltage appears at the terminals of the coil. Conversely, for the formation of a magnetic flux, it is enough to pass an electric current through the coil.
Thus, to obtain alternating electric current, a coil is required through which a direct electric current flows, forming a magnetic flux, called a field winding, and a steel pole system, the purpose of which is to bring the magnetic flux to coils called a stator winding, in which an alternating voltage is induced.
These coils are placed in the grooves of the steel structure, the magnetic core (iron package) of the stator. The stator winding with its magnetic circuit forms the generator stator itself, its most important stationary part, in which the electric current is generated, and the excitation winding with the pole system and some other parts (shaft, slip rings) - the rotor, its most important rotating part.
When the rotor rotates opposite the stator winding coils, the "north" and "south" poles of the rotor appear alternately, that is, the direction of the magnetic flux penetrating the coil changes, which causes an alternating voltage to appear in it.
The stator winding of generators of foreign companies, as well as domestic ones, is three-phase. It consists of three parts, called phase windings or simply phases, in which the voltage and currents are displaced relative to each other by a third of the period, that is, by 120 electrical degrees. The phases can be connected in a "star" or "triangle".
Generator device.
According to their design, the generator sets can be divided into two groups - generators of traditional design with a fan at the drive pulley and generators of the so-called compact design with two fans in the inner cavity of the generator. Usually "compact" generators are equipped with a drive with a high gear ratio through a poly-V-belt and therefore, according to the terminology accepted by some companies, are called high-speed generators. At the same time, within these groups, generators can be distinguished, in which the brush assembly is located in the inner cavity of the generator between the pole system of the rotor and the rear cover, and generators, where slip rings and brushes are located outside the inner cavity. In this case, the generator has a casing, under which there is a brush assembly, a rectifier and, as a rule, a voltage regulator.
The generator device is shown in the photo. The housing (5) and the front cover of the generator (2) serve as supports for the bearings (9 and 10) in which the armature (4) rotates. The voltage from the battery is supplied to the armature excitation winding through the brushes (7) and slip rings (11). The armature is driven by a V-belt through a pulley (1). When starting the motor, as soon as the armature starts to rotate, the electromagnetic field it creates induces an alternating electric current in the stator winding (3). In the rectifier unit (6), this current becomes constant. Further, the current through a voltage regulator combined with a rectifier unit enters the car's electrical network to power the ignition system, lighting and alarm systems, instrumentation, etc. will be enough to ensure the smooth functioning of all consumers.
Precautionary measures
The operation of a generating set requires compliance with some rules, mainly related to the presence of electronic components.
1. It is not allowed to operate the generating set with the battery disconnected. Even a short disconnection of the battery while the generator is running can lead to failure of the voltage regulator elements.
When the battery is completely discharged, it is impossible to start the car, even if it is towed: the battery does not provide excitation current, and the voltage in the on-board network remains close to zero. The installation of a working charged battery helps, which then, when the engine is running, changes to the old, discharged one. In order to avoid the failure of the voltage regulator elements (and connected consumers) due to an increase in voltage, during the replacement of the batteries, it is necessary to turn on powerful consumers of electricity, such as heated rear window or headlights. In the future, for half an hour or an hour of engine operation at 1500-2000 rpm, the discharged battery (if it is in good working order) will be charged enough to start the engine.
2. It is not allowed to connect electricity sources of reverse polarity (plus on "ground") to the on-board network, which can occur, for example, when starting the engine from an external storage battery.
Similar information.
In practice, several types of generators are used. But each of them includes the same building blocks. These include a magnet, which creates the appropriate field, and a special wire winding, where an electromotive force (EMF) is generated. In the simplest model of the generator, the role of the winding is played by a frame that can rotate around a horizontal or vertical axis. The EMF amplitude is proportional to the number of turns on the winding and the amplitude of the magnetic flux oscillations.
To obtain a significant magnetic flux, a special system is used in generators. It consists of a pair of steel cores. The windings, which create an alternating magnetic field, are placed in the slots of the first of them. Those turns that induce EMF are laid in the grooves of the second core.
The inner core is called a rotor. It rotates around the axis along with the winding on it. The core that remains motionless acts as a stator. To make the flux of magnetic induction the strongest, and the energy losses to be minimal, they try to make the distance between the stator and the rotor as small as possible.
What is the principle of the generator
The electromotive force arises in the stator windings immediately after the appearance of an electric field, which is characterized by vortex formations. These processes are generated by a change in magnetic flux, which is observed during accelerated rotation of the rotor.
The current from the rotor is supplied to the electrical circuit using contacts in the form of sliding elements. To make this easier, rings called contact rings are attached to the ends of the winding. Fixed brushes are pressed against the rings, through which the connection between the electrical circuit and the winding of the moving rotor is carried out.
In the turns of the magnet winding, where a magnetic field is created, the current has a relatively small strength when compared with the current that the generator gives to the external circuit. For this reason, the designers of the first generators decided to divert the current from the statically arranged windings, and to supply a weak current to the rotating magnet through the contacts providing sliding. In low power generators, the field creates a permanent type magnet that can rotate. This design allows you to simplify the entire system and do not use rings and brushes at all.
A modern industrial generator of electric current is a massive and bulky structure, which consists of metal structures, insulators and copper conductors. The device can be several meters in size. But even for such a solid structure, it is very important to maintain the exact dimensions of the parts and the gaps between the moving parts of the electric machine.
