DIY generator from an induction motor. Asynchronous electric motor as a generator Can an electric motor generate electricity
Alas, interruptions in the supply of electricity to some areas may occur even now, in the 21st century. No matter what the reason for such interruptions: at least a break in the line due to poor conditions, at least a planned shutdown.
In any of the cases, the consumer cannot always easily endure several hours without electricity. Here generators come to the rescue for the summer house and the private sector in general.
An autonomous generator for generating electricity seems to be the most optimal solution not to remain without electricity and continue to live and use household appliances to the envy of neighbors.
So buy, and first consider options for autonomous stations - this is a priority.
What are the generators
Before choosing a generator for a summer residence, you need to know their main differences. And this, in turn, can affect performance and several other factors. To date, the three most popular types:
- gasoline generator;
- diesel generator;
Already from the name it becomes clear that the difference is in the form of fuel, which runs an autonomous installation. However, it would not make sense for mankind to come up with several types of voltage producers, and most likely there are certain differences between these three types.
Firstly, gasoline, diesel fuel and gas - for each in their own way available. There is no need, we believe, to purchase a gasoline generator if a gas main is connected to the house. After all, the cost of gas is still more acceptable than the cost of gas. On the other hand, having in stock several liters of gasoline or diesel fuel, you can be sure that the simultaneous shutdown of electricity and gas will not interfere with your work.
The second thing that deserves attention is the work of household generators on different types of fuel. Some produce more noise during operation, others less; some are more dimensional, others are more compact; some are easy to start in any weather, others may have problems starting in cold weather.
Choose a unit for private use
Diesel or gas, or maybe gas - this is quite important. But it is equally important to take into account other features that need to be selected:
Noise at work
Gasoline and diesel generators have the only significant drawback - a fairly noticeable noise level in working condition . This disadvantage is to some extent a prerequisite for work. You must admit that you have never encountered a silent engine.
A similar situation is observed here: when the engine rpm is generated, a certain noise is generated. Given that the installation usually works for a rather long time and the monotonous sound annoys not only the owners, but also the neighbors, you need to find a solution to this problem.
According to the rules of fire safety, the generator for a country house should be installed in a well-ventilated room. If you build a separate room with supply and exhaust ventilation, the sound level will partially decrease.
How much - depends on the materials used in construction. However, this will require additional costs, effort and time. The feasibility of this idea is determined by the weight of the installation. An autonomous generator of large sizes, which will not be rearranged from place to place, is likely to require such a room.
Construction practice also often knows cases when a pit with bricked walls and a roof was built on the site for gasoline or diesel generators. While ensuring air circulation and maximum tightness, it is possible to sufficiently reduce the noise level from a working device.
Instead of a conclusion
The fact that the generator is able to simplify our lives is a long-proved theorem. Even, most likely, an axiom that does not require special evidence. Failures that can occur during operation do not mean at all that the unit is not worthy of attention.
If we are talking about factory marriage, it means that just a person trusted in a low-quality manufacturer. And if the breakdown is the fault of the owner, then why blame the unit? Buying a generator is a useful acquisition if you can use it correctly.
Electric motors are sometimes called "secondary" because the energy for them must first be generated using a "primary" motor and an electric generator. But these smokeless and almost silent, powerful and durable engines managed to take first place among others.
From the beginning of the 19th century it is known that a wire with a current placed between the poles of a magnet begins to move. If you make a frame from any conductor and let current flow along its contour, the frame will rotate 90 degrees. If you take a lot of such frames and pull them on a common drum, and put powerful magnets around, you get a direct current electric motor. The drum is called an anchor, and the ends of the frames - turns - are attached to a switchgear - collector - on the armature shaft.
A collector is a set of plates isolated from each other, which during rotation of the shaft alternately touch two fixed metal brushes. A constant current is applied across the brushes to the collector plates. It passes through the frame at the moment when the brushes touch the collector plates connected to it. And then, together with the anchor, the collector turns, two other plates approach the brushes, and the next frame receives current.
DC motors can quickly gain speed of rotation of the shaft and change it at our discretion. They can easily reverse, starting to rotate in the opposite direction.
However, most power plants do not produce direct, but alternating current.
And therefore, in order to supply them with a direct current electric motor, alternating current is pre-rectified. There are also electric AC motors, capable of directly consuming current from the network without rectification. In such engines, the fixed part (housing) is called the stator. On the inner surface of the stator there are three windings, three separate coils with wires located at an angle of 120 degrees to each other.
When an electric current is passed through such a winding, it becomes an electromagnet. The coils are connected so that alternating current is supplied to them not simultaneously, but with a time shift. The magnetic field of each coil is amplified, then weakened, then completely disappears. As a result, it turns out that the magnetic field runs along the inner surface of the stator. This traveling, “rotating” field can entrain the conductor, since at the first moment, when the conductor is still stationary, a vortex of magnetic field lines excites an electric current in it. Further motion completely obeys the laws of motion of a conductor with current in a magnetic field.
As a moving part, called the rotor, they usually use a winding of wire, or make a "squirrel wheel" - a cage in the form of a cylinder with parallel rods. The ends of the rods are connected with copper rings.
An alternating current is supplied to the stator winding of the electric motor, and a moving magnetic field arises. Following the field, the rotor begins to rotate, doing useful work.
But the speed of the rotor never reaches the speed of rotation of the magnetic field - it is always slightly behind, and the magnetic field “glides” around the rotor. Without such a slip, motor operation is impossible, since the currents necessary for movement in a magnetic field will not be induced in the rotor. Because of this phenomenon, such motors are called asynchronous, that is, non-simultaneous.
Electric motors have no equal efficiency - they convert more than 90% of the supplied electricity into useful work. However, one should not forget that after all, the electric motor is secondary, and when generating electric energy for it, other energy losses are unavoidable on the primary engines, during energy transfer, etc.
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Not always, local electricity networks are able to fully provide electricity at home, especially when it comes to suburban cottages and mansions. Interruptions in the constant power supply or its complete absence makes us look for electricity. One such use is - a device capable of converting and storing electricityusing for this the most unusual resources (energy, tides). Its principle of operation is quite simple, which makes it possible to make an electric generator with your own hands. Perhaps a home-made model will not be able to compete with the analog of the factory assembly, but this is a great way to save more than 10,000 rubles. If we consider a home-made electric generator as a temporary alternative source of power supply, then it is quite possible to do with home-made.
We will find out how to make an electric generator, what is required for this, and also what nuances will have to be considered.
The desire to have an electric generator in its use is clouded by one nuisance - this is high unit cost. Say what you like, but the most low-power models have a rather sky-high cost - from 15,000 rubles and more. It is this fact that leads to the idea of \u200b\u200bthe creation of a generator with your own hands. However himself the process can be difficult, if:
- no skill in working with tools and circuits;
- no experience in creating such devices;
- the necessary parts and spare parts are not available.
If all this and a great desire are present, then you can try to assemble a generatorguided by the assembly instructions and the attached diagram.
It is no secret that the purchased generator will have a more expanded list of features and functions, while a homemade product can fail and fail at the most inopportune moments. Therefore, to buy or do it yourself is a purely individual issue, requiring a responsible approach.
How does an electric generator work?
The principle of operation of the electric generator is based on the physical phenomenon of electromagnetic induction. A conductor passing through an artificially created electromagnetic field creates a pulse that is converted to direct current.
The generator has an engine that is capable of generating electricity by burning a certain type of fuel in its compartments:, or. In turn, fuel entering the combustion chamber produces gas during the combustion process, which rotates the crankshaft. The latter transmits momentum to the driven shaft, which is already able to provide a certain amount of energy at the output.
To solve the problem of limited fossil fuels, researchers around the world are working on the creation and implementation of alternative energy sources. And this is not only about all known windmills and solar panels. Gas and oil can be replaced by energy from algae, volcanoes and human steps. Recycle chose the ten most interesting and environmentally friendly energy sources of the future.
Turnstile joules
Thousands of people pass through the turnstiles every day at the entrance to the railway stations. Immediately in several research centers around the world the idea came up to use the flow of people as an innovative energy generator. The Japanese company East Japan Railway Company decided to equip each turnstile at the railway stations with generators. The installation works at a train station in the Shibuya district of Tokyo: piezoelectric elements are built into the floor under the turnstiles, which produce electricity from the pressure and vibration that they receive when people step on them.
Another technology of energy-turnstiles is already used in China and in the Netherlands. In these countries, the engineers decided not to use the effect of pressing on the piezoelectric elements, but the effect of pushing the turnstile handles or turnstile doors. The concept of the Dutch company Boon Edam involves the replacement of standard doors at the entrance to shopping centers (which usually work on a photocell system and begin to spin themselves) with doors that the visitor needs to push and thus generate electricity.
In the Dutch center Natuurcafe La Port, such generator doors have already appeared. Each of them produces about 4600 kilowatt-hours of energy per year, which at first glance may seem insignificant, but serves as a good example of an alternative technology for generating electricity.
The article describes how to build a three-phase (single-phase) 220/380 V generator based on an asynchronous AC motor. Three-phase asynchronous electric motor, invented at the end of the 19th century by the Russian scientist-electrician M.O. Dolivo-Dobrovolsky, has now received predominant distribution in industry, and in agriculture, as well as in everyday life.
Asynchronous electric motors are the simplest and most reliable in operation. Therefore, in all cases where this is permissible under the conditions of the electric drive and there is no need for compensation of reactive power, asynchronous AC motors should be used.
There are two main types of induction motors: squirrel cage rotor and with phase rotor. An asynchronous squirrel-cage motor consists of a fixed part - a stator and a moving part - a rotor rotating in bearings mounted in two motor shields. The stator and rotor cores are composed of separate sheets of electrical steel isolated from one another. A winding made of an insulated wire is laid in the grooves of the stator core. A core winding is placed in the grooves of the rotor core or molten aluminum is poured. The jumper rings short-circuit the rotor winding at the ends (hence the name - short-circuited). Unlike the squirrel-cage rotor, in the grooves of the phase rotor is placed a winding made by the type of stator winding. The ends of the winding lead to the contact rings mounted on the shaft. Brushes glide along the rings, connecting the winding to the starting or adjusting rheostat.
Asynchronous motors with a phase rotor are more expensive devices, require qualified service, less reliable, and therefore are used only in those industries that cannot be dispensed with. For this reason, they are not widespread, and we will not consider them in the future.
A current flows through the stator winding included in the three-phase circuit, creating a rotating magnetic field. Magnetic lines of force of a rotating stator field intersect the rods of the rotor winding and induce an electromotive force (EMF) into them. Under the influence of this EMF, current flows in short-circuited rotor rods. Around the rods, magnetic fluxes arise, creating a common magnetic field of the rotor, which, interacting with the rotating magnetic field of the stator, creates a force that causes the rotor to rotate in the direction of rotation of the magnetic field of the stator.
The rotor speed is slightly less than the frequency of rotation of the magnetic field generated by the stator winding. This indicator is characterized by slip S and for most engines is in the range from 2 to 10%.
In industrial installations, the most commonly used three-phase asynchronous electric motorswhich are issued in the form of unified series. These include a single 4A series with a range of rated power from 0.06 to 400 kW, the machines of which are highly reliable, have good performance and comply with international standards.
Autonomous asynchronous generators are three-phase machines that convert the mechanical energy of a primary engine into electrical energy of alternating current. Their undoubted advantage over other types of generators is the lack of a collector-brush mechanism and, as a consequence of this, great durability and reliability.
Asynchronous electric motor in generator mode
If the asynchronous motor disconnected from the mains is brought into rotation from any primary motor, then in accordance with the principle of reversibility of electric machines when the synchronous speed is reached, some emf is formed at the terminals of the stator winding under the influence of the residual magnetic field. If a capacitor bank C is connected to the terminals of the stator winding, then the leading capacitive current will flow in the stator windings, which in this case is magnetizing.
The battery capacity C must exceed a certain critical value C0, depending on the parameters of the autonomous asynchronous generator: only in this case the generator self-excites and a three-phase symmetrical voltage system is installed on the stator windings. The voltage value depends, ultimately, on the characteristics of the machine and the capacitance of the capacitors. Thus, an asynchronous squirrel-cage motor can be turned into an asynchronous generator.
The standard scheme for switching on an induction motor as a generator.
You can choose the capacity so that the rated voltage and power of the asynchronous generator are equal to the voltage and power, respectively, when it is used as an electric motor.
Table 1 shows the capacitance of the capacitors for the excitation of asynchronous generators (U \u003d 380 V, 750 ... .1500 rpm). Here, the reactive power Q is determined by the formula:
Q \u003d 0.314 · U 2 · C · 10 -6,
where C is the capacitance of the capacitors, microfarads.
| Power of the generator, kV · A | Idling | |||||
| capacitance, microfarad | reactive power, kvar | cos \u003d 1 | cos \u003d 0.8 | |||
| capacitance, microfarad | reactive power, kvar | capacitance, microfarad | reactive power, kvar | |||
| 2,0 3,5 5,0 7,0 10,0 15,0 |
28 45 60 74 92 120 |
1,27 2,04 2,72 3,36 4,18 5,44 |
36 56 75 98 130 172 |
1,63 2,54 3,40 4,44 5,90 7,80 |
60 100 138 182 245 342 |
2,72 4,53 6,25 8,25 11,1 15,5 |
As can be seen from the above data, the inductive load on the asynchronous generator, which reduces the power factor, causes a sharp increase in the required capacity. To keep the voltage constant with increasing load, it is necessary to increase the capacitance of the capacitors, that is, connect additional capacitors. This circumstance must be considered as a disadvantage of the asynchronous generator.
The speed of the asynchronous generator in normal mode should exceed the asynchronous one by the amount of slip S \u003d 2 ... 10%, and correspond to the synchronous frequency. Failure to fulfill this condition will lead to the fact that the frequency of the generated voltage may differ from the industrial frequency of 50 Hz, which will lead to unstable operation of frequency-dependent consumers of electricity: electric pumps, washing machines, devices with transformer input.
A decrease in the generated frequency is especially dangerous, since in this case the inductive resistance of the windings of electric motors and transformers decreases, which can cause them to become more heated and cause premature failure.
As an asynchronous generator, a conventional asynchronous squirrel-cage electric motor of appropriate power can be used without any alterations. The power of the electric motor-generator is determined by the power of the connected devices. The most energy-intensive of them are:
- household welding transformers;
- power saws, electric shakers, grain crushers (power 0.3 ... 3 kW);
- electric furnaces of the type "Rossiyanka", "Dream" with a capacity of up to 2 kW;
- electric irons (power 850 ... 1000 W).
I especially want to focus on the operation of household welding transformers. Their connection to an autonomous source of electricity is most desirable, because when working from an industrial network, they create a number of inconveniences for other consumers of electricity.
If a household welding transformer is designed to work with electrodes with a diameter of 2 ... 3 mm, then its apparent power is approximately 4 ... 6 kW, the power of an asynchronous generator for its power supply should be within 5 ... 7 kW. If a household welding transformer allows operation with electrodes with a diameter of 4 mm, then in the most difficult mode - “cutting” the metal, the total power consumed by it can reach 10 ... 12 kW, respectively, the power of the asynchronous generator should be within 11 ... 13 kW.
As a three-phase capacitor bank, it is good to use so-called reactive power compensators designed to improve cosφ in industrial lighting networks. Their type designation: KM1-0,22-4,5-3U3 or KM2-0,22-9-3U3, which is deciphered as follows. KM - cosine capacitors impregnated with mineral oil, the first dimension figure (1 or 2), then the voltage (0.22 kV), power (4.5 or 9 kvar), then the number 3 or 2 means three-phase or single-phase execution, U3 (temperate climate of the third category).
In case of independent manufacture of the battery, capacitors such as MBGO, MBGP, MBGT, K-42-4 and others should be used for an operating voltage of at least 600 V. Electrolytic capacitors cannot be used.
The above option for connecting a three-phase electric motor as a generator can be considered classic, but not the only one. There are other methods that have proven themselves in practice as well. For example, when a capacitor bank is connected to one or two windings of an electric motor-generator.
Two-phase mode of the asynchronous generator.
Fig. 2 Two-phase mode of an asynchronous generator.
Such a circuit should be used when there is no need to obtain a three-phase voltage. This inclusion option reduces the working capacity of the capacitors, reduces the load on the primary mechanical engine in idle mode, etc. saves "precious" fuel.
As low-power generators producing alternating single-phase voltage of 220 V, it is possible to use single-phase asynchronous squirrel-cage electric motors for domestic use: from washing machines such as "Oka", "Volga", irrigation pumps "Agidel", "BCN", etc. They can have a capacitor bank connect in parallel to the working winding, or use an existing phase-shifting capacitor connected to the starting winding. The capacity of this capacitor may need to be slightly increased. Its value will be determined by the nature of the load connected to the generator: for an active load (electric furnace, light bulbs, electric soldering irons) a small capacity is required, inductive (electric motors, televisions, refrigerators) - more.
Fig. 3 Low-power generator from a single-phase induction motor.
Now a few words about the primary mechanical engine that will drive the generator into rotation. As you know, any conversion of energy is associated with its inevitable losses. Their value is determined by the efficiency of the device. Therefore, the power of a mechanical motor must exceed the power of an asynchronous generator by 50 ... 100%. For example, with an asynchronous generator power of 5 kW, the power of a mechanical motor should be 7.5 ... 10 kW. Using the transmission mechanism, coordination of the revolutions of the mechanical engine and the generator is achieved so that the operating mode of the generator is set at medium revolutions of the mechanical engine. If necessary, you can briefly increase the power of the generator, increasing the speed of the mechanical engine.
Each autonomous power station must contain the required minimum of attachments: an alternating current voltmeter (with a scale of up to 500 V), a frequency meter (preferably) and three switches. One switch connects the load to the generator, the other two switch the excitation circuit. The presence of switches in the excitation circuit facilitates the starting of the mechanical engine, and also allows you to quickly reduce the temperature of the generator windings, after the end of work - the rotor of the unexcited generator is rotated from the mechanical engine for some time. This procedure extends the active life of the generator windings.
If using a generator it is supposed to power equipment that is normally connected to an alternating current network (for example, residential building lighting, household electrical appliances), then it is necessary to provide a two-phase switch that will disconnect this equipment from the industrial network during the operation of the generator. It is necessary to disconnect both wires: "phase" and "zero".
In conclusion, a few general tips.
1. The alternator is a hazardous device. Use voltage of 380 V only in case of emergency, in all other cases use voltage of 220 V.
2. According to safety requirements, the generator must be equipped with grounding.
3. Pay attention to the thermal mode of the generator. He "does not like" idling. Heat load can be reduced by a more careful selection of the capacitance of exciting capacitors.
4. Make no mistake with the power of the electric current generated by the generator. If one phase is used during the operation of a three-phase generator, then its power will be 1/3 of the total power of the generator, if two phases - 2/3 of the total power of the generator.
5. The frequency of the alternating current generated by the generator can be indirectly controlled by the output voltage, which in the "idle" mode should be 4 ... 6% higher than the industrial value 220/380 V.
