What are the disadvantages of induction generators
Induction generator definition. Generators: device, technology, application functions
The development of the automotive industry went hand in hand with an increase in the requirements for the reliability and service life of motor vehicles, the convenience of their operation and the reduction of the operating costs for technical service and repair, as well as compliance with the ever-increasing traffic safety requirements.
In this regard, there has been a need to significantly increase the performance and life of automotive alternators as the main sources of electrical power in order to improve their operating characteristics and reduce operating costs. There was a need to reduce the overall dimensions and mass of the generators, as well as many other units and devices, which made it possible to flexibly design the layout and external design of cars and to save on expensive metals.
Meeting these requirements by improving the design and production technology of direct current generators, taking into account the poor reliability and short service life of the brush collector assembly, and overall dimensions and mass of direct current generators, became impracticable. Therefore, a new direction has been taken in the development of vehicle generators - the creation of alternators.
The name "alternator" is a bit arbitrary and mainly relates to the design features of the generator, as they are equipped with built-in semiconductor rectifiers and supply the consumers with direct current.
In direct current generators, such a rectifier is a brush collector unit that rectifies the alternating current taken up in the armature windings.
The development of semiconductor technology made it possible to use a more advanced and reliable rectifier for semiconductor diodes in alternators that did not have mechanical parts and components that were subject to wear and failure.
Advantages and disadvantages of generators
The main advantages of generators compared to DC generators include the following characteristics:
- with the same power, their mass is 1.8 ... 2.5 times less, and about three times less valuable non-ferrous metal is consumed - copper;
- Generators produce more power with the same dimensions;
- electricity begins to be generated at a lower rotor speed;
- simpler circuit and construction of the control device due to the lack of a current limiting element and the reverse relay
- simpler and more reliable design of the pantograph, especially in the case of non-contact alternators;
- lower operating costs due to high reliability and longer service life.
From a practical point of view, the advantages of an alternator are that the current it generates is diverted from the fixed windings attached to the stator housing. The field winding, which is implemented on a rotating rotor, is much lighter than the fixed stator windings, so that the rotor can be rotated at a higher speed without having to fear unbalance phenomena in the rotating masses. And the excitation current is easier to bring in this case because it is small. This means that brushes and slip rings last longer.
In addition, unlike an AC generator, a DC generator begins to generate electricity at a relatively high rotation frequency of the armature. For this reason, for its full functionality, for example when the engine is idling, a considerable gear ratio of the drive is required, which in the future (at the operating frequency of the crankshaft) can lead to imbalances (due to the considerable weight of the armature), wear of bearings and generator drive elements.
A certain advantage of alternators is also shown in the fact that if high voltage is required (for example, to supply high-voltage consumers with electricity), it is sufficient to use a small transformer. It is not possible to increase the DC voltage in this way. Despite the fact that the need for high voltage is extremely rare in automotive electrical systems, this possibility cannot be ruled out.
The main disadvantages of the alternator are the need to rectify the electricity it generates, as well as a certain power loss in the metal parts surrounding the rotor and stator due to the appearance of eddy and reactive currents in an alternating electromagnetic field. Nevertheless, the advantages of generators pay off more than the disadvantages mentioned.
The first alternators for automobiles were developed to operate with separate selenium rectifiers and vibration voltage regulators. Selenium rectifiers had considerable dimensions and had to be placed separately from the generator in places where good cooling was guaranteed. To connect such a rectifier to the generator, additional wiring was required.
In addition, selenium rectifiers were not heat-resistant enough and allowed a maximum working temperature of no more than +80 ° C.
For these reasons, they later rejected selenium rectifiers and started using silicon diodes, which were smaller in size and had good heat resistance, which made it possible to place them directly in the generator.
The vibration voltage regulators were replaced by contact transistors and then contactless on discrete elements and contactlessly integrated regulators.
The overall dimensions of the integrated regulator enable integration into a generator, which together with the built-in regulator and rectifier unit is referred to as a generator set.
Scheme of an alternator
On fig. 1 A simplified diagram of an alternator is presented, which consists of two main parts: a fixed-winding stator, in which alternating current is induced, and a rotor, which creates a magnetic field.
The rotor poles alternately pass the stationary stator coils, which are located in the grooves on the inside of the generator housing. In this case, the direction of the magnetic flux changes and, consequently, the direction of the EMF induced in the coil.
Usually you get the number of magnetic poles on the rotor and the number of coils in the housing three-phase current. In three-phase generators, the windings have a common point where their ends are connected. Therefore, this connection scheme is called "star" and the common point of the winding is called the zero point.
The second ends of the windings are connected to a half-wave rectifier. The magnetic field of the rotor can be generated by a permanent magnet or an electromagnet. In the latter case, an electromagnet is connected to the excitation winding with constant voltage.
The use of electromagnets in the rotor complicates the construction of the generator, since the rotating part - the rotor - has to be supplied with voltage. In this case, however, it is possible to regulate the voltage by changing the rotor speed. In addition, the magnetic properties of permanent magnets depend significantly on their temperature.
The device and the mode of operation of the motor vehicle generator are specified in detail.
Contactless generators with electromagnetic excitation
The reliability and service life of vehicle generators are determined by three factors:
- electrical insulation quality;
- quality of storage units;
- the reliability of current-consuming (brush contact) devices.
The first two factors depend on the level of development of the related industries. The third factor can be eliminated by using non-contact generators with higher reliability and longer life than contact generators with brush contact current collectors. This stimulated the creation of non-contact vehicle generators with electromagnetic excitation - inductor generators and generators with shortened poles.
Electromagnetic excitation non-contact generators include inductor generators and short-beaked generators. The generator works as follows. The excitation winding, through which direct current flows, creates a flux in the magnet system that changes in size as the rotor rotates without changing its sign. This flow is closed and passes through the air gap between the shaft and the rotor elements, the teeth of which are designed in the shape of an asterisk, the air gap between the rotor and the stator, the stator magnetic circuit and the generator cover.
A change in the magnetic flux in the armature during the rotation of the rotor occurs due to a change in the magnetic resistance of the air gap between the teeth of the stator and the rotor.
Magnetic flux F. in pulsating induction generators. The magnetic flux in the air gap changes periodically F maxwhen the axes of the teeth of the rotor and stator coincide to F minwhen the axes of the teeth of the rotor and stator are offset by an angle 180 ° electrical grade. Thus, the magnetic flux has an average constant and variable component with amplitude
F Lane \ u003d 0.5 (f max - f min)
The 3 prongs and the cavity of the rotor (inductor) of the generator form a pair of poles, so the frequency of the armature current in the inductor of the generator can be determined by the formula:
f \ u003d zn / 60
where z is the number of teeth on the rotor.
In the case of generators with shortened poles, contactlessness is achieved through the fixed installation of the field winding with a non-magnetic cage. The beak-shaped poles are less than half the length of the active part of the rotor. During the rotation of the rotor, the magnetic flux of excitation crosses the turns of the stator winding and induces emf in them.
Shortened pole generators are simple in design and technologically advanced. The rotors of such generators show little spread.
The disadvantages are a slightly larger mass than contact generators with the same power. Attention should also be paid to the difficulty of attaching the field winding and ensuring the rigidity and mechanical strength of its attachment.
The use of existing designs of inductor generators in automobiles has long been limited by the following difficulties:
- low specific indicators;
- increased ripple of the rectified voltage;
- increased noise level.
A further improvement in the design and the elimination of the above disadvantages made it possible to use induction generators on automobiles.
For the first time, brushless generators with shortened poles 45.3701 and 49.3701 were used in UAZ vehicles.
A short video will give you a clear understanding of the basic principles of how an alternator works and how to set up.
"And why is it actually needed?" - many readers will reasonably ask. It turns out that most of such a unit is simply necessary, and each buyer has his own reasons.
Pampered by city dwellers who once saw a friend on a picnic generatorI can no longer imagine resting outside the city without this "miracle".
For others, a station is sometimes the only source of power because of problems with a central network or because it is not there.
Repair crews, emergency services, cottage, store, and gas station owners - this is not an exhaustive list of the customers of companies that sell generators.
So it turns out that very different people for very different purposes decide sooner or later to buy their own autonomous "socket". This is how you have to perceive a modern, compact, economical and quiet gasoline (diesel) power plant.
You must know
When choosing a generator, they are usually based on personal preferences. Give someone mobility and light weight, someone else needs the ability to automate and extend the work without interruption, while someone else wants both at the same time but inexpensively. In any case, however, it is necessary to solve the problem of choosing the unit with the appropriate performance. First, let's try to figure out what it is - "electricity"?
How do you calculate the required generator power?
Take, for example, a 2-kilowatt heater, a 1-kilowatt vacuum cleaner, and a 300-watt freezer. What are such different burdens in common? It turns out that it is necessary to "drive" each of them electric generator with an output of at least 3 kVA
Two sensitive questions arise. First: Why is the same quantity (power) given in different units: kW and kVA? And secondly: Why can consumers of electrical energy (we have a heater, a vacuum cleaner and a freezer) not be “cut in a single comb”?
What is a power factor?
It is known from physics that power is equal to the product of voltage and current. Hence, it makes sense that it should be measured in volt-amps, or VA. This is the total or apparent power. The latter is divided into two components.
Active (useful) is used directly for performing work that is typical of a particular electrical appliance. This "visible" part is measured in watts or watts. Reactive, measured in reactive volt-amps (var), is used to generate magnetic fields in coils and electrical fields in capacitors.
After interaction with reactive loads, the sinusoids of current and voltage are shifted against each other by a certain angle Phi. The closer it is to 0 (cos Phi - \ u003e 1), the greater the useful power, since at some point the maximum values of voltage and amps are multiplied. According to the rules, devices with cos Phi less than 0.7 may not be connected to the network.
Now we're going to answer the second question. Let's start with a vacuum cleaner: why is it impossible to fully realize in terms of this generator power?
The electrical resistance of the vacuum cleaner also has an inductive reactive component. The main culprit is the electric motor with its windings, which add a phase difference of their own with the same sign (direction) to the phase difference of the generator (alternating current generator) of the power plant. As a result, another power factor has to be applied that characterizes the energy consumer.
Electric generator or alternatorconverts, as experts often call it, the mechanical rotational energy of the motor shaft into electromagnetic alternating current energy. Depending on the type and design, the power plant is suitable for solving various problems.
Synchronous or asynchronous?
To excite EMF (electromotive force) An alternating magnetic field must be generated in the stator windings (the stationary part of the generator). This is achieved by rotating the magnetized rotor (its other name is the armature). Various methods are used for magnetization.
So u synchronous generator at anchor there are windings to the electric current. By changing its value, the magnetic field and thus the voltage at the output of the stator windings can be influenced. The easiest way to play the role of the regulator is perfect circuit with feedback of current and voltage. Because of this, the ability of the synchronous generator to swallow brief overloads is very high and is only limited by the ohmic (active) resistance of its windings.
However, this scheme also has disadvantages. First, the power must be fed to a rotating rotor, which traditionally uses a brush arrangement. With larger currents (especially with overload) the brushes overheat and partially burn out. This leads to a poor fit of the collector, an increase in the ohmic resistance and further overheating of the arrangement. In addition, the mobile contact inevitably sparkles, which means that it becomes a source of radio interference.
To avoid premature wear, it is recommended that the condition of the brush assembly be checked from time to time and that the brushes be cleaned or replaced if necessary. By the way, after the replacement it is advisable to give them time to get used to the collector and then to charge the station “fully”.
Many of the most modern synchronous generators equipped with brushless current excitation systems on the rotor coils (they are also known as brashless). They are deprived of the above disadvantages and so it is preferable.
Generally it has no windings on the rotor. The residual magnetization of the armature is used to excite the EMF in its output circuit. Structurally are e.g. alternator much easier, more reliable and more durable. In addition, since the rotor windings do not have to be cooled (they simply do not exist), the asynchronous generator housing can be closed, thus practically preventing the ingress of dust and moisture.
Unfortunately, asynchronous devices are not without their drawbacks, either. The voltage stability at the output is usually worse than that of synchronizers. And the possibility of triggering overloads leaves a lot to be desired: When a certain critical current value is reached in the stator windings, the rotor is simply demagnetized. However, it is not difficult to magnetize - just apply the voltage indicated in the instructions for specific inputs.
The listed "asynchronous problems" are partially solved by equipping the stations with a voltage regulator and a starting amplifier. However, all these "bells and whistles" rob the unit of its main advantage - simplicity.
How many phases does it have?
Indeed, why do we need three incomprehensible phases when you cannot figure it out with one? But the fact is that without it - nowhere - it works. To begin with, three-phase circuit connection allows you to transfer the power from three single-phase sources in just three wires (in the case of a single-phase circuit, two wires would have to be allocated for each such source).
As a result, the alternator is more compact, lighter and more efficient with the same output power. It is also more versatile: both 220 volts for household use and 380 volts for industry are output at the output.
Everyone, even the most beautiful alternator It does not give a watt of power if it is not turned by the motor. What are they and how do they differ?
Usually on gas power plants Low and medium power carburetors or, as they are often called, gasoline engines are used (the very correct term is "internal combustion engine with external mixture formation").
As the name suggests, the fuel for them is gasoline. It burns, gives some of its energy to the piston and does useful work. All that's left is to heat up the atmosphere and engine parts. Of course, the more joules that go into useful business, the better.
Increasing efficiency is a difficult technical task for which they resort to various techniques.
It was possible to make a qualitative leap in the fight to reduce fuel consumption during the transition to over-valve engine design. One of these schemes, with a camshaft in the crankcase and a rod drive, has become the most widespread in recent years and is called an OHV. Its implementation made it possible to reduce the surface area of the combustion chamber, and therefore reduce the heating of engine parts. In addition, when the same brand of gasoline was used, it became possible to increase the compression ratio (from 5 to 6 to 7 to 9 units), further increasing efficiency.
Unfortunately, further increasing the efficiency of a gasoline engine due to an increase in the compression ratio is impractical - it requires a significant increase in the octane number of the fuel (i.e. its cost). Otherwise, the exploding combustible mixture will burn prematurely and push the piston against its movement.
For the next qualitative step it is necessary to radically improve the mixture formation process itself, ie to dispense with the carburettor in favor of electronically controlled injection systems. And the price of the simplest of them is very close to the cost of a cheap engine with its carburetor.
Diesel power plants have unattainably low fuel consumption for a gasoline engine. Its compression ratio is limited mainly by the strength and heat resistance of parts of the piston and crank groups. For normal operation in harsh operating conditions, diesel engines must have a very long service life, that is, they must be heavy. As a result, at high shaft speeds they wear out faster than the lighter parts of the carburetor engine. The foregoing in no way means that the diesel engine is any less durable (here is the time to recall the high safety margin), it just explains the reason it prefers lower revs.
Such a motor has two serious disadvantages: high cost and relatively large mass. We will not consider the complexity and high repair costs - they are compensated for by reliability and durability.
Briefly summarize the problem of choosing the type of power plant as follows:
- Every diesel engine is more economical than a gasoline engine and usually manages to compensate for the price difference through its "decline".
- The slow-running diesel engine (1500 rpm) outperforms the gas engine by four to five times and two to three times its weight. "High-Speed" (3000 rpm) is about one and a half times ahead of the carburettor engine in both parameters.
- If the design does not include glow plugs (and these are usually only available on very powerful engines), starting a diesel engine at low temperatures is very difficult.
- In winter, you need to use special types of fuel on a diesel engine.
Two and four stroke engines
In terms of design, two-stroke engines are simpler and accordingly cheaper, lighter and more reliable (sometimes also more durable) four-stroke engines. The downside of the coin is increased fuel consumption and the need to tinker with oil (it must be served along with gasoline).
But there is a silver lining: oil thickening in the cold does not prevent the scrolling of a cold engine, each revolution of which, by the way, corresponds to two "four-stroke cycles". Anyone who works or lives in the north knows this very well and prefers such engines. Getting a frozen "four-stroke" is almost impossible and there is no time for savings ...
Glossary of terms
API - Evidence that the performance level of the oil is determined according to the standards of the American Petroleum Institute. The first letter of the index after the API abbreviation indicates the category: S - for gasoline engines, C - for diesel engines.
The second is a quality group. The lowest grade is for oils with the letter “A”, the highest grade is “B” etc. If the designation is duplicated, e.g. B. API SJ / CF, the fat can be used as both SJ and CF.
AVR - stands for Automatic Voltage Regulator. This system is installed on synchronous generators to stabilize the output voltage (usually it is supported with an accuracy of 5%). For a precise (exact) setting, they use additional electronic devices, which are usually purchased for a fee.
Sae - means that the oil viscosity grade is determined according to the standards of the Society of Automotive Engineers of the United States. Winter classes are designated as numbers with the index W (from winter - winter), for example SAE 5W; Summer - only by number, for example, SAE 30; and universal - a combination of both by a hyphen, for example, SAE 5W-30. Incidentally, for engines that are lubricated by spraying, viscosity is particularly important. Oil that is too thick does not form an “oil mist” and therefore does not get into the friction vapors.
The thermal machine without a fuse - Designed to protect the generator from overload. Today it is the most common current protection device.
Brushless generator - Synchronous generator, in the design of which there are no brushes. It is maintenance-free, durable and does not cause any radio interference during operation. Powerfully displaces traditionally designed generators from the market for small and medium-sized devices.
Decompressor - When started manually, it automatically opens one of the motor's valves, making it easier for the shaft to run up to the desired speed. Almost all four-stroke engines (diesel and petrol) with a manual starter are equipped with this device.
Differential leakage protection - ordinary RCD, now it should be in every apartment. Purpose - to increase safety when working with the generator. The fact is that the culprit of most injuries is the current flowing between the phase and the ground. Example: A person stands on the frame of a generator and touches an uninsulated wire. An ordinary automaton will not work in this situation - the load is too small, but the differential protection will necessarily open the circuit.
Oil level protection - It is intended on all modern engines. If the level falls below the critical level, it switches the motor off or signals this. In engines with an oil pump, it is usually not the level that is regulated, but the oil pressure in the working circuit.
Protection class according to DIN 40050 - The German standard according to which the alternator is protected from external influences. It is indicated by two letters (IP) and two numbers.
The first digit means:
0 - no protection;
1 - protection against foreign objects larger than 50 mm;
2 - protection against contact with fingers and against the ingress of solid foreign objects with a diameter of more than 12 mm;
3 - protection against foreign objects and particles with a diameter of more than 2.5 mm;
4 - protection against contact with tools, fingers and wire with a diameter of more than 1 mm, protection against ingress of solid foreign objects with a diameter of more than 1 mm;
5 - complete protection against contact with tools of any kind and against dust.
The second digit means:
0 - no protection;
1 - protection against vertically falling drops of water;
2 - protection against drops of water falling at an angle of 15 degrees from the vertical;
3 - protection against jets of water falling at an angle of up to 60 degrees from the vertical;
4 - protection against water dust escaping from all sides;
5 - Protection against jets of water falling from all sides at any angle.
Profitability systems - The economy mode is activated either manually or automatically when power consumption is reduced to a critical level. At the same time, the station's engine runs slower, which means you can use significantly less fuel and reduce noise.
Boost system - to improve the overload capacity. With asynchronous devices it is usually not possible to achieve the results characteristic of synchronizers. Incidentally, the start reinforcement system in the latter case is usually a safety machine with special properties.
Pressure lubrication - contributes to long-term operation of the engine with little wear and tear and little maintenance. Such a system, if available, filters the oil, which means that it extends the life of the lubricant and improves the stability of its properties. Its use is justified for expensive engines with high performance and part load.
Fuel pump (fuel pump) - With gasoline power plants, you can place the fuel tank (or additional tanks) below the carburetor level, and with diesel power plants - place the tanks much lower than the engine (e.g. on the lower floor of the building or even underground). Pumps are manufactured with mechanical (directly attached to the motor), electrical or pneumatic (vacuum) drive.
Choke control - An air valve is required for the artificial enrichment of the working mixture (the so-called mixture of air and gasoline produced by the carburettor). This contributes to the easy and safe starting of the engine, especially at low temperatures. Before starting, the shutter should be closed and opened after warming up. There are both simple systems with a vacuum drive and more complex systems with a vacuum drive and temperature sensor. (If the valve is controlled manually - the power plant cannot be started remotely without automation.)
Glow plugs - serve to make it easier to start a diesel engine at low temperatures. Usually they are installed on powerful motors (for an additional fee).
What distinguishes diesel operation? In order to avoid detonation and increase the degree of compression, it is better to supply fuel to the cylinder with air not in advance, but at the time of ignition. This is how a diesel engine works, in which the compression is so great that the temperature of the compressed air is sufficient for spontaneous combustion of fuel. A separate ignition system is therefore not required.
A high pressure fuel pump is used to inject fuel into the nozzles. The design is not complicated, but it does require very precise machining and assembly of the parts. In the event of failure or wear and tear, it is usually not repaired and despite the high cost (up to 1/3 the cost of the entire engine), they are completely replaced. It's just unrealistic to fix it in "field conditions" - we don't consider trivial cases like a loose nut.
Typical malfunctions in fuel systems that can be “treated” include all types of filter blockages and the “freezing” of the nozzle shut-off needle. Not to say it's easy, but if you want, you can take care of it yourself.
Why use a special "diesel fuel" in winter? Unlike gasoline, diesel fuel is saturated with various impurities, most of which (by weight) relate to paraffins. In summer they do not manifest themselves, but in winter they crystallize at negative temperatures, making the liquid more viscous. When their content is large, "diesel fuel" turns into "jelly" or even "jelly". solid body ". And if it is not enough, the crystals formed will clog the fine fuel filter, even if the viscosity remains normal.
In order not to get into trouble, you need to switch timely to winter types of fuel or use special additives. If the contents of the tank already resemble a piece of jelly, it will definitely not help - look for a blowtorch. The use of such drugs is necessary in advance (in extreme cases - at the stage of cloudiness of the fuel).
What distinguishes a two-stroke engine? With each revolution of the crankshaft (i.e. two cycles), each cylinder of such an engine succeeds in "digesting" part of the fuel, while the "four-stroke engine" needs two revolutions to do this. The consequences are less friction loss and almost twice as much performance, all other things are the same.
Exhaust and suction strokes are combined with a working stroke and replaced by a "flush". As a result, the piston “loses” part of its energy and the combustible mixture not only gets into the cylinder, but also into the exhaust pipe. To "blow" use the space under the piston, the back of which acts as the piston of the compressor.
Hence, you need to supply oil with fuel because you can no longer pour it into the crankcase. Motors with a closed lubrication system are an exception, but are usually not used for small devices.
Why are generators called "synchronous" and "asynchronous"? As you know, an electric motor is a reversible machine, which means that it can not only consume electricity but also generate it. The electric motor and the electric generator are practically the same (small differences only in design). By the way, the alternators got their name from engines.
Consider three inductors arranged in a circle. Each of them has an alternating current, the phases of which are shifted from each other by 120 degrees (this is exactly the angle between two adjacent coils). The sum of their magnetic fields forms a vector of constant length that rotates at a frequency equal to the frequency of the alternating current flowing through the windings.
When a cylindrical rotor (armature) made of conductive material is inserted into such a stator, it begins to rotate according to the magnetization vector. The greater the difference between the rotational frequencies and the total field of the coils, the greater the torque acting on them. The nature of this work is asynchronous (the rotor speed is out of sync with the frequency of change of the stator field). This is a three-phase electric motor operating scheme (one could consider a single-phase one, but the situation is less obvious there).
In order for such a motor to become a generator (generator), its rotor must be not only a conductor, but also a magnet (that is, magnetization). Of course, it works synchronously, that is, the frequency of the electricity generated is exactly the same as the rotor speed, but is called asynchronous, analogous to the motor.
The synchronous electric motor is arranged differently. In this case, the rotor is not a conductor, but an electromagnet. If a current is supplied to the windings of the armature, it starts moving and rotates until the direction of its magnetic moment coincides with the direction of the magnetic moment of the stator. In order for the rotor to continue rotating, the direction of the current in the windings must be changed. And so every half a turn. It can be seen that the frequency of change of the alternating magnetic field corresponds exactly to the rotor speed. Hence the name - synchronous electric motor. To turn such a motor into an alternator, its design is changed a little, but the principle of operation remains the same.
Which brands of generators are the most popular? The main generator manufacturers: Generac (England), Leroy Somer (France), Mecc Alte (Italy), Metallwarenfabrik Gemmingen (Germany), Sawafuji (Japan), Sincro (Italy), Soga (Italy), Stanford (England), Yamaha ( Japan)) etc.
The most common brands of engines. Gasoline engines are manufactured by Briggs & Stratton (USA), Honda (Japan), Kubota (Japan), Lombardini (Italy), Mitsubishi (Japan), Robin (Japan), Suzuki (Japan), Tecumseh (Italy), Yamaha (Japan ), Etc. . produced. Finding a generator with a household gasoline engine is almost impossible.
Diesel engines are manufactured by Acme (Italy), Hatz (Germany), Honda (Japan), Iveco (Italy), Kubota (Japan), Lombardini (Italy), Robin (Japan), Yamaha (Japan), Yanmar (Japan), Etc. . Domestic diesel engines are manufactured in Vyatka, Tula, Chelyabinsk, Vladimir, Rybinsk and Yaroslavl, but are usually installed in powerful power plants.
A car generator, which is certainly part of the equipment of every vehicle, can be compared to the role of a power station in supplying energy to the national economy.
It is the main source of power (when the engine is running) in the car and is designed through electrical cables to entangle the entire car from the inside to maintain a predetermined and stable voltage of the car's power supply. The functional principle of a vehicle generator is based on a theoretical representation of the operation of a classic electrical generator that converts non-electrical forms of energy into electrical energy.
In the special case of a car generator, electrical energy is generated by converting a mechanical rotary movement of the crankshaft of the engine unit.
General principle of work
The theoretical assumptions underlying the operation of electricity generators are based on the well-known case of electromagnetic induction, conversion of one type of energy (mechanical) into another (electrical). The effect of this effect can be seen when copper wires are placed in the form of a coil and placed in a magnetic field of variable size.
This contributes to the appearance of an electromotive force in the wires that drives the electrons. This movement of electrical particles creates an electrical voltage at the connection contacts of the wires, the level being directly dependent on how quickly the magnetic field changes. The alternating voltage generated in this way must be fed to an external network.
In an automobile generator, stator windings are used to create a magnetic phenomenon in which the rotor armature rotates under the influence of a field. There are conductive windings on the armature shaft, which are connected to special contacts in the form of rings. These ring contacts are also attached to the shaft and rotate with it. From the rings with the help of conductive brushes electrical voltage and supply of the generated energy 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 motor unit, which is started by the battery source in order to start operation. In order to ensure efficient conversion of the generated energy, the diameter of the generator disk should be significantly less than the diameter of the crankshaft friction wheel. This higher shaft speeds for the generator ensures set. Under these conditions, it works with an increase in its efficiency and provides increased current characteristics.
In order to ensure safe operation in a certain range of properties of the entire complex of electrical devices, the operation of a vehicle generator must meet high technical parameters and ensure the generation of a voltage level that is stable over time.
The main requirement for vehicle generators is stable power generation with the required performance characteristics. These parameters are intended to provide:
- simultaneous operation of all participating electrical devices;
- stable mains voltage in a wide range of speed changes of the rotor shaft and dynamically connected loads;
In addition to the above parameters, the generator has been designed with its critical load operation in mind and must have a robust housing, light weight, and acceptable overall dimensions, as well as a low and acceptable level of industrial radio interference.
The device and design of the automobile generator
The auto generator can be easily identified in the engine compartment by lifting the hood cover. There it is attached to the front of the engine with screws and special angles. Assembly paws and a clamping eye of the device are located on the generator housing.
Almost all devices of the device are built into the generator housing. Light metals based on aluminum are used for production, which are ideal for heat dissipation. The housing construction consists of two main parts:
- front cover on the side of the slip rings;
- end caps on the drive side;
Brushes, a voltage regulator and a rectifier bridge are attached to the front cover. The combination of the covers in a single housing construction is done using special screws.
The inner surfaces of the covers fix the outer surface of the stator and fix its position. Important structural units of the housing construction are also the front and rear bearings, which create the conditions for the rotor to function and which fasten it to the cover.
The structure of the rotor assembly consists of an electromagnetic circuit with an excitation winding mounted on a bearing shaft. The shaft itself is made of alloy steel with additions of lead.
Copper contact rings and special spring-loaded brush contacts are also attached to the rotor shaft. Contact rings are responsible for the power supply to the rotor.
The stator assembly consists of a core with numerous slots (36 in most cases) that hold the turns of three windings that are in electrical contact with one another in either a "star" or "triangle" pattern. The core, also known as the magnetic circuit, consists of a hollow, spherical circle of metal plates that are pulled together by rivets or welded into a single monolithic block.
To increase the magnetic field strength on the stator windings in the manufacture of these plates, transformer iron with improved magnetic parameters is used.
This electronic unit was developed to compensate for the rotational stability of the rotor shaft, which is connected to the crankshaft of the vehicle engine and operates over a wide speed range. The voltage regulator is connected to graphite current collectors and helps to stabilize a certain constant output voltage that is fed to the machine's electrical network. In this way, it guarantees the uninterrupted operation of electrical equipment.
According to their design decision, the regulatory authorities are divided into two groups:
The first type comprises electronic units, on the construction plate of which radio elements are mounted, which were developed in discrete (housing) technology and are characterized by a suboptimal density of the arrangement of the elements.
The second type includes the majority of modern electronic voltage control devices designed taking into account the integrated method of arranging radio elements made on the basis of thin-film microelectronic technology.
Due to the fact that a constant voltage is required for the correct functioning of the on-board devices, the generator output feeds the vehicle network via an electronic node that is built on powerful rectifier diodes.
This three-phase six-phase rectifier semiconductor diodes, three of which are connected to the negative pole (ground) and the other three to the positive pole of the generator, which is designed to transform alternating voltage into constant. Physically, the rectifier unit consists of a horseshoe-shaped metal heat sink with rectifier diodes arranged on it.
This assembly looks like a plastic construction and is designed to transfer stress to the slip rings. Inside the housing there are several elements, the most important of which are spring-loaded sliding contacts. They come in two modifications:
- copper-graphite (more wear-resistant).
Structurally, the brush assembly is often made in one unit with a voltage regulator.
The dissipation of excess heat that arises inside the generator housing is ensured by fans that are mounted on the rotor shaft. Generators, whose brushes, voltage regulators and rectifier units are brought out outside the housing and protected by a special housing, suck in fresh air through special cooling slots.
Impeller for external cooling of the generator
The device has a classic design. By arranging the above nodes within the generator housing, fresh air is supplied from the contact rings.
Modes of operation
In order to understand the principle of operation of the vehicle generator, it is necessary to introduce how the vehicle generator works.
- initial start-up time;
- engine operating mode.
When the engine is first started, the main and only consumer of electrical energy is a starter. The generator is not yet involved in the generation of energy, and the power supply currently only provides the battery. Due to the fact that the strength of the current consumed in this circuit is very large and can reach hundreds of amperes, previously stored electrical energy consume intensely.
After completion of the starting process, the engine goes into operating mode and the generator simultaneously becomes a full-fledged electricity supplier. It generates the electricity necessary for the functioning of various electrical devices that are connected to work. Together with this function, the generator charges the battery while the engine is running.
After a set of batteries is required, the need for charging is reduced, power consumption drops noticeably, and the generator continues to only support the operation of electrical devices. Since other resource-intensive electricity consumers are connected to the plant, at certain times the generator power may not be enough to provide the total load, and then in joint work the battery turns on, the operation of which in this mode is characterized by a rapid loss of charge.Mas Motors
Autonomous generators are often indispensable, and the full list of their possible uses is very long - from powering a beach party on the weekend to keeping it at work in a private building all the time. From a large number of works, a large number of autonomous generator types have emerged, which differ both in their construction and in their properties. What they have in common is the operating principle: an internal combustion engine of one type or another rotates the shaft of an electrical generator and converts mechanical energy into electrical energy.
The most obvious breakdown of generator groups is professional and domestic.
- A household generator is usually a portable unit with a non-continuous gasoline engine with an output of several kVA.
- Professional generators have a higher output and a longer service life. In order to save fuel and save resources, diesel engines are usually installed. If household electrical generators produce a single-phase current with a voltage of 220 V, then professional generators are mostly three-phase and designed for 380 V of the output voltage. Thanks to their large dimensions and weight, powerful generators can either be mounted on a chassis or set up stationary.
We have already identified a number of design differences in this classification. Let's look at them in order.
As you know, a gasoline engine can work in push-pull as well as in four-stroke. At the same time, because of their low efficiency and limited resources, two-stroke engines are not in great demand to power an electric generator, even though they are simpler, which means cheaper and simpler.
The four-stroke engine, though it is harder and more expensiveconsumes significantly less fuel and able to work a lot more. Generators with an output of up to 10 kVA are therefore usually equipped with motors of this type.
- These are mainly single-cylinder units with external air cooling, the preparation of the combustible mixture takes place via a carburetor. Either a cable starter or an electric starter is used for starting (in this case such generators have a 12 V output in addition to the battery: the battery is charged via this circuit and consumers for low-voltage electricity can be connected). The most common cast iron sleeve and overhead valve timing engines are typically Honda GX engines and their Chinese counterparts.
Motors for domestic gas generators not suitable for continuous operation. Exceeding the operating time specified in the instruction manual (usually no more than 5-7 hours) will reduce the resources of the engine.
However, also the most advanced gasoline engines have a limited resource: With proper care, they work 3-4 thousand hours. Is it a lot or a little? With occasional use on the street, for example, to hook up a power tool - this is a fairly large resource, but constantly private house from a gas generator means to sort out your engine annually.
Significantly diesels have a greater resource In addition, the units are more profitable in continuous operation due to their higher efficiency. For this reason, all powerful generator sets, both portable and stationary, use diesel engines.
For such units, a number of disadvantages of diesel engines compared to gasoline (high cost, higher weight and noise generation) are not fundamental, there is a certain inconvenience only when starting diesel engines in cold weather.
Please note this during operation long work on idle no charge harmful to them: The completeness of combustion of fuel is violated, which leads to increased soot formation, clogging of the exhaust gas and dilution of the engine oil, with diesel fuel seeping through the piston rings. Therefore, the list of routine maintenance for diesel engines inevitably includes regular performance at full power.
Generators also work there. Structurally, they are no different from gasolinewith the exception of the power supply system: instead of the carburetor, they are equipped with a gearbox to regulate the gas pressure and a calibrated nozzle to supply gas to the intake manifold. In addition, as a source of fuel, such generators can use not only a cylinder with liquefied gas, but also a gas network - in this case, the cost of fuel will be minimal. The disadvantage of such generators is their low mobility (a gas cylinder is larger and heavier than a gas tank, which can also be refueled on site) and an increased risk of fire, especially in the illiterate sector. But as a source in a house connected to the gas pipeline, this is a good option: there is no need to pay attention to the level and quality of fuel in the gas tank, and engine resources are higher when working with gas than when working with gas working with gasoline.
This is the main unit of the gas generator, which determines its characteristics and scope. The principle of its action is to excite the current in a fixed stator winding with alternating current. magnetic field generated by a rotating winding (rotor) in synchronous generators or a permanent magnet c. The number of stator windings determines the number of phases at the output:
- Single-phase generators have a power winding, such a scheme is common in household generators of small and medium power;
- Three-phase generators have three power windings and can supply both a load designed for three-phase power supply of 380 volts and single-phase consumers (in this case, with such a circuit, they must be divided into three groups of equal power) .
The power of the generator is closely related to the number of phases and the general structure:
- Power-saving generators (up to 2 kVA) are light petrol units that are not intended for professional use. Their typical application is the energy supply of street sales outlets.
- Medium power generators (up to 6.5 kVA) - this technology belongs to the semi-professional and professional class, but it is quite compact. Gasoline engines are also used. A similar generator can provide power to a workshop or small house.
- Both diesel engines, which often have more than one cylinder, can be found under high-performance units (up to 15 kVA). High power makes the use of a single phase circuit impractical. Therefore, such generators often have a three-phase output voltage of 380 V, and more powerful generator sets are made exclusively three-phase.
In addition to the high-voltage winding, many generators are equipped with an additional winding that feeds loads that are designed for 12 V DC via a rectifier: Safe transport, car compressors, etc.
The type of excitation of the generator depends on its power and range. Asynchronous generators are much simpler and cheaper. Synchronous due to the lack of field winding and brush arrangement, and their resource is higher. On the other hand, with synchronous generators you can easily and precisely control the output voltage by varying the winding current and work better even with sudden load changes, especially with high inductances - for example when connecting - powerful electric motor The size and duration of the voltage drop is higher with an asynchronous generator. For this reason, asynchronous circuit gas generators are often supplied with a special trigger amplification system that briefly increases the power output by the generator.
The functional principle of the asynchronous generator is shown in the video
There is another important parameter of alternating current that should not be forgotten - frequency. And if for a number of consumers, such as incandescent lamps, it does not matter much, then for power supplies, electronic equipment, a deviation in the frequency of the supply voltage from the rated voltage is fraught with not only a violation of their work , but also damage.
The frequency of the electricity generated by the generator is determined by two parameters: the rotor speed and the number of poles on it. Therefore, a bipolar rotor needs to be rotated at a frequency of 3000 rpm to generate a current with a frequency of 50 Hz, and a four-pole rotor should be rotated at 1500 rpm. The set speed is maintained by a mechanical controller that regulates the carburetor throttle on petrol generators or the high-pressure fuel pump on diesel. Such a mechanism is simple and quite effective under a constant load, whereas if there is a large change in power consumption, the frequency will change for a short period of time. In addition, the need to maintain a constant frequency forces the generator motor to constantly operate at the same maximum power speeds, even though the motor could deliver power at lower speeds with low power consumption - hence the reduction in engine life and increased fuel consumption.
These shortcomings were avoided with the advent of widespread access to powerful switching electronics that made it possible to create. The operating principle of the inverter is simple: the alternating current generated by the generator is rectified and then converted by the electronics unit back into a changing but already precisely defined frequency. This makes the frequency of the output voltage absolutely independent of the rotor speed of the generator and allows the motor to change the speed depending on the load, saving resources and fuel.
Cheap inverters can usually produce voltage shape removed from the ideal sine wave. Connecting a strong inductive load to such an inverter lead to overheating and possible damage Inverter output stage!
Inverter generators have certain disadvantages: due to the presence of electronic unit they are more expensive than traditional gas generators and theoretically less reliable. In addition, the possibilities of power electronics are not unlimited, and the maximum power of inverter generators now does not exceed 7 kVA.
The video shows the device of a gas generator using the example of a model from the Zubr brand
When choosing a generator, you need to start with determine the required performance. This question is not as simple as it seems, since consumers in AC circuits have both an active (ohmic) resistance and a reactive (capacitive and inductive) and often a much higher nominal current consumption before they switch to the operating mode.
The simplest example: We need a portable generator from which we feed an 800 W hammer drill. Its electric motor has a significant inductive resistance component, which is described by the so-called power factor (cosφ) when calculating the energy consumption. If, for a load that has no reactance, it is equal to one, then the greater the capacitance or inductance, the greater the load. In addition, we must not forget that the generator itself has significant inductance.
Precisely inductive reactance on the windings of the generator, its power is given not in watts, but in volt-amps for a given power factor: for example, a 5 kVA gas generator with its own cosφ \ u003d 0.8 because actually has a maximum power of 4 kW
In order to operate an 800 watt electric motor with its own cosφ \ u003d 0.5, we therefore need a generator that can deliver a power of 1600 W over a long period of time, that is, its peak power specified in the characteristics should be one and a half to Be twice. Taking into account the losses in the generator itself, we need to buy a 4 kVA gas generator for our hammer drill.
At the same time, if we need to have lighting and an electric heater from the same generator (loads that do not have reactance), their total output can be twice as large with the same load on the generator itself.
Next we determine the operating time of the generator. As mentioned earlier, for long-term operation, a diesel generator set is preferable - therefore, given the fact that the generator set continuously powers a building (a private house or a small workshop), it makes sense to consider this option, especially taking into account the above calculation of the required generator power - the gas generator is too voracious. Since a long-running generator cannot be constantly monitored, it must be equipped with a protective device that switches off the engine if the engine oil level or the pressure drops.
In some cases (the need for frequent transport, especially manual transport), a lower mass of the inflator may turn out to be a more important factor than diesel economy. A petrol unit is preferable for short-term operation - in this case, economy and resources play a much smaller role than the price of the system itself.
For the emergency power supply of the house, the possibility of connecting a generator designed for the use of natural gas to the gas network should be considered.
The portable generator must be placed on a flat, dry surface and protected from rain when working outdoors. Since single-cylinder engines used in gas generators vibrate heavily, foreign objects and especially fuel tanks must not be placed on the generator to prevent it from falling.
Make sure before you start sufficient engine oil and refill if necessary, after which the generator motor can be started.
The load can only be connected to the generator after the engine has started. Do not start the generator with electrical devices connected to it.
A special air flap is used to start the petrol engine to enrich the fuel mixture in the closed position. When the engine is started for the first time, especially in cold weather, the lower the air temperature, the more it needs to be closed and gradually open as the engine warms up.The warmed up engine should start without covering the damper, otherwise you should pay attention to the carburetor settings.Depending on the motor construction, the start is either carried out with a pull-wire starter (pull it out carefully to feel resistance, then increase the force significantly) or electrically (press and hold the start button to start).
Starting a diesel engine differs only in that no air damper has to be used, but rather that the decompressor has to be opened, a device that reduces the pressure in the combustion chamber to make it easier to start the crankshaft when starting. In addition, the start of a diesel engine can be significantly hindered by an airy fuel system (starting a new generator for the first time or if the tank has previously run dry). In this case, you need to pump the fuel system (the pumping sequence is different for different engines and is described in the owner's manual).
If you let the generator run for a while (in the warm season the gas engine heats up quickly enough, no more than a minute), you can connect the load and make sure that the operating indicators or the voltage indicator of the generator set indicate full operation.
Timely maintenance of the generator set noticeably affects its resource. The engine, as the most complex unit, requires the most frequent attention. The air filter must be replaced and serviced according to the frequency in operating hours specified by the manufacturer. In the case of powerful generators with more complex engines, the oil and fuel filters also change. Gasoline engines (much less gasoline) need to be replaced with spark plugs.
If the generator is used sporadically, it is not worth keeping it full. Oxidation and decomposition can clog carburetor deposits on Benogen generators and paraffin escapes in diesel engines, which can completely block the fuel intake. Even old fuel makes starting difficult.
The generator itself is practically a perpetual assembly, only from time to time it is necessary to clean the brush assembly of the synchronous generator from dust and change the brushes themselves, and sometimes the rotor bearings.
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