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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Wind power plant based on an asynchronous electric motor. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Alternative energy sources The problems of cheap energy excite the minds of many. They didn't spare me either. But, as it turned out, the trouble is the beginning. Issues in the design and construction of the station arose almost immediately. Here are just a few of them: "Which generator to use?", "How to achieve stability of the output voltage with strong changes in the wind, the speed of which ranges from 2 to 25, or even 30 m / s?", "What to do when the wind disappears completely ?", How to unload a wind turbine during strong storms and hurricanes?", "What to do in cases when there is wind, but energy is not used, or, conversely, when energy is needed, but there is no wind?", "How to save and use excess energy more efficiently?" and, finally, "Which design of the "windmill" is better?". Both automobile generators and synchronous motors were used as a generator. But both options have the same drawback: too high wind turbine rotor speed is needed, and this, in turn, leads to an increase in the gear ratio of the gearbox, and hence an increase in the dimensions of the wind wing. This also adds a large frequency instability and the difficulty of reliable stabilization of the output voltage, and in the case of using a synchronous motor, also large dimensions and weight. During a long search, preference was given to a generator based on an asynchronous motor with a squirrel-cage rotor. The advantages of this generator are truly impressive: small dimensions and weight with a sufficiently large power; no need for excitation voltage; if you use a low-speed motor, then the power of the rotor can be reduced; the output frequency is practically independent of the rotational speed of the generator rotor. However, there is a significant drawback: this generator cannot be overloaded. The circuit for switching on an asynchronous motor with a squirrel-cage rotor is shown in Fig. 1.
Technical characteristics of the wind turbine:
When the motor rotor rotates, the residual magnetic field acts on one of the stator windings. In this case, a small electric current arises, which charges one of the capacitors C1-C3. Due to the fact that the phase of the voltage on the capacitor lags behind by 90 °, a magnetic field of an already greater magnitude arises on the rotor, which acts on the next winding. Accordingly, the next capacitor will be charged to a higher voltage. This process continues until the generator rotor enters saturation (1...1,5 s). After that, you can turn on the machine B2 and use the energy generated by the generator. Moreover, for normal operation of the engine in the generator mode, the load power should be no more than 80% of the engine used as a generator. The remaining 20% is used to maintain the voltage on the capacitors, i.e. keeping the generator running. If this condition is exceeded, the voltage on the capacitors will disappear, which means that the magnetic field at the armature will also disappear, which will lead to the disappearance of voltage at the terminals of the machine B2. And it happens almost instantly. This has its disadvantage and its advantage. The disadvantage is that re-energization is possible only when the cause of the overload is eliminated and the B2 circuit breaker is turned off. The generator will enter the operating mode again (after 1...1,5 s). After that, you can turn on B2 and use energy. The advantage is the fact that the generator is almost impossible to burn, since the voltage at its terminals disappears instantly, within 0,1 ... 0,5 s. The output voltage has a sinusoidal shape and is fully suitable for further use. The output frequency of the generator is 46...60 Hz, which in most cases is sufficient for home use. Due to the instability of the voltage at the output of the generator, it was necessary to make stabilizer. A few words about additional capacitors. The table shows the capacitance of capacitors per kilowatt of installed motor power, and for work with a load - additional capacitance per kilowatt of load. For example, there is a 3 kW motor. It is supposed to connect a reactive load (electric motor, welding machine ...) to it with a total power of approximately 2 kW. At the same time, we want 380 V between the phases. This means that the capacitance of the capacitor C1 will be (3x5) + (2x6) microfarads. Since C1 \u2d C3 \u30d C450, then we need three capacitors with a capacity of 630 microfarads. If there is no capacitor of the required capacitance, then capacitors of a smaller capacitance can be connected in parallel. Capacitors should be paper or metal paper for a voltage of at least 220 V, and preferably 127 V. From my experience, I can say that it is best to turn on the generator for voltage between phases of 45 V, and between zero and phase XNUMX V. This is due to the fact that that for normal operation of the generator, the phase imbalance should not exceed XNUMX °. Wiring in this case can be done according to the diagram shown in Fig. 2. With this scheme, it is possible to unload the generator as much as possible.
In addition, it is better to power incandescent lighting lamps and some heating devices with direct current. The generator must use a low-speed squirrel-cage motor. A 360-720 rpm motor is best, but a 910 rpm motor will do. This is due to the need to rotate the rotor at about twice the speed than indicated in the passport for the engine, and a decrease in the gear ratio of the gearbox. The wind turbine itself can be made according to any scheme convenient for you. I propose the following construction. The wind turbine is a combination of Dare and Savonius rotors, which is slightly simplified and refined. The principle of operation is shown in Fig. 3 and needs no explanation.
The wind turbine (Fig. 4) consists of a wind wing 1, support 2 and the generator itself 3. The support is rigidly concreted and reinforced with three tension cables 4. The support can be made of wood, concrete, metal.
You can use a support that is used to transmit electricity, or a pile. As extensions, it is better to use a steel cable with a diameter of 6 ... 9 mm or a steel wire with a diameter of 10 ... 12 mm. The crutches for which the stretch marks are attached also need to be well concreted. The frame of the wings of a wind turbine can be made from pipes with a diameter of 1 inch, its drawing is shown in Fig. 5.
Ailerons can be made from a steel bar with a diameter of 6 mm. A thick-walled pipe with a diameter of 2...2,5 inches was used as the drive shaft, with a shaft 300...400 mm long pressed into its lower end. A groove for the pulley is made at the lower end of the shaft. Bearings are taken spherical with conical clamps brand 2000810 with corresponding housings. After assembly, the wing must be balanced. The assembled wing is attached to the support in any convenient way, but the main thing is that the fastening is sufficiently rigid and reliable. It was experimentally found that the best material for wrapping the wing is a polyethylene film with a thickness of 80 ... 120 microns. It is strong enough, light and cheap, and allows you to abandon the brake mechanism, which, by the way, is unacceptable in this device, since the wing will be destroyed in strong winds. It is necessary to cover with plastic wrap in several layers, soldering at the seams with a soldering iron through a piece of polypropylene film. I recommend you practice soldering first. The soldered seam must be even and strong. The wing, of course, can be covered with other materials, such as canvas, plywood or even metal, but you need to think about a device that will allow you to unload it in strong winds. Covering with metal or plywood is not recommended due to the increased mass of the wing. The frame itself can be made of duralumin, which will reduce its weight, but this material is more expensive. A wing made of pine slats with a section of 50x50 mm was also tested, but the result was not very good, since it was blown to pieces during the first strong wind. A gearbox is used to drive the generator shaft. You can use a gearbox of any system, except for a worm gear. As already mentioned, the generator shaft must be rotated at about twice the speed, and the wind turbine shaft rotates at a speed of 500 rpm with a wind speed of 5 m / s. Hence the restriction on the engines used as a generator. A 360 rpm motor might be the best option, but a 720 rpm motor can also be used. When using a 910 rpm engine, you need to increase the height of the wing by 500 mm. It is not recommended to increase the width of the wing, since this will reduce the rotational speed, it should not be reduced either, since with an increase in the rotational speed, the power will greatly decrease, and the law of decrease is non-linear. When selecting a gearbox, you should be guided by the following rule: for the nominal speed of the wind turbine wing, you need to take the value of 500 rpm, which corresponds to a wind speed of 5 m/s, the motor shaft speed increases by 2,3, then by simple calculations we obtain the transmission coefficient The option of fastening the generator to the support using a belt reducer is shown in Fig.6. The bracket itself is easy to attach to the support using six studs. With a gear reducer, mounting is much easier.
I do not recommend making the wind turbine shaft too long, as it can simply be twisted. Installation of the wind turbine must be carried out in calm weather using safety belts and mounting claws. The entire structure must be grounded. Grounding resistance should be no more than 2 ohms. At the foot you need to install a cabinet in which it is necessary to place capacitors C1-C3, automata B1-B2, diodes V1-V6, a voltage stabilizer, a control machine, four batteries and a powerful voltage converter to provide electricity during calm times. The automatic control provides switching of power supply circuits depending on the load and wind speed. A powerful voltage converter provides battery charging while the generator is idling, as well as power supply from the batteries in the absence of wind or a very low voltage on the generator. When there is no wind and the batteries are discharged, the automatic control provides power supply from the standard network. Unfortunately, the automatic control and a powerful voltage converter are not included in the scope of this article. The cable used to connect the generator and the power cabinet must be three-phase with a core cross section of not more than 4 mm2. The cables used to connect the cabinet to consumers can be the same. The ground bus must have a cross section of at least 12 mm2. Attention! All work on the installation of electrical installations must be carried out with the B1 machine turned off and the capacitors C1-C3 discharged. Many problems still could not be solved. For example, how to store unused energy so that it can be used in times of calm? Ordinary lead and alkaline batteries did not show the best results. I hope that readers will also be interested in this problem, and a solution will still be found. This generator can be connected to an internal combustion engine and used as a ballast generator. However, fuel for such engines still needs to be bought, and this is not very profitable. The capacitances of the capacitors included in the phases, in microfarads per 1 kW of power, are given in the table:
Author: V.V. Chirka
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