Although the speed of wind power generation is slow, the fans used in wind power generation are very large. This type of fan can generate a lot of force with each rotation. This will therefore produce electricity.
Wind turbines use wind energy to turn machines, driving the generator rotor and causing the stator to produce electrical energy. There are two types of wind turbines: medium-high speed dual-feed type and low-speed permanent magnet type. The dual-feed unit is equipped with a gearbox that can change the speed of the blades from a low speed to over $1,000. a dozen revolutions at medium-high speed (above a thousand revolutions) to adapt to the generator to produce electricity.
The low speed permanent magnet generator can operate at a low speed of more than ten revolutionss due to its large number of magnetic poles and its ability to convert low-frequency electrical energy into industrial frequency electrical energy through a frequency converter for use. Therefore, although the wind speed is high, the rotation speed of the blade is very low, but suitable electrical energy can be produced and used using mechanical and electrical methods.
In single-phase power supply, the generator power is P=UIcosΦ. In three-phase power supply, the generator power is P=1. In three-phase power, the power is divided into. three types: power P and no power Q and apparent power S. The cosine of the phase difference (Φ) between voltage and current is called power factor, represented by the symbol cosΦ. Numerically, the power factor is the ratio between active power and apparent power.
That is to say that cosΦ=P/S. Lhe three powers and the power factor cosΦ are a right-angled power triangle relationship: the two right-angled sides are the power P and the non-power Q, and the hypotenuse is the apparent power S. In a three-phase load, these three powers always exist at the same time: S=P+Q S=√(P+Q) Apparent power S=1 Power P=1 No power Q=1 Power factor cosΦ=P/ S .
Notes
The main sources of wind are gravity and the sun. The sun causes uneven heating of the ground and atmosphere, leading to differences in density between atmospheres. of gravity, an atmospheric circulation is formed. The gas flow forms wind, which acts on the blades of the wind turbine, causing the blades to rotate, similar to a water turbine, and then drives the generator to do work, converting the wind energy into electrical energy.
The principle of wind energy production is actually the samethan that of hydroelectric production. They convert the mechanical energy existing in nature into electrical energy, which is an easy to transport and different form of use. , he benefits from the discovery of the electromagnetic effect.
The source of mechanical energy is due to the existence of Earth's gravity. The greater the water drop, the higher the pressure and the higher the efficiency of the generator drive. Hydroelectricity production begins with a hydraulic turbine. It is directly influenced by water, then the hydraulic turbine drives the generator.
Reference for the above content: Baidu Encyclopedia - Wind Turbine
The differences between horizontal axis and vertical axis wind turbines lie in the following aspects:
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For the design of horizontal axis wind turbine blades, the theory of moment blade elements is commonly used. The main methods include Glauert method, Wilson method, etc. but, Since blade element theory ignores flow interference between each blade element and airfoil resistance is ignored when designing blades using blade element theory, this simplification inevitably leads to inaccuracy in the results. This simplification has a negative impact on the blade. the shape design has a small impact, but it has a greater impact on the wind energy utilization rate of the wind turbine. At the same time, the interference between the blades of the wind wheel is also very strong, and the entire flow is very complex. It is impossible to obtain accurate results based on blade element theory alone.
The design of vertical axis wind turbine blades was formerly based on the horizontal axis design method and relieshas on the theory of blade elements. Since the flow of vertical axis wind turbine is more complex than that of horizontal axis, it is a typical large separation unsteady flow and is not suitable for analysis and design using blade element theory. This is also an important reason for the vertical axis. The wind turbine has not been developed for a long time.
2. Wind power utilization rate
The wind power utilization rate of large horizontal axis wind turbines is mainly calculated by blade designers and is generally above 40%. As mentioned earlier, due to flaws in the design method itself, the accuracy of wind energy usage calculated in this way is highly questionable. Of course, wind turbines at wind power plants will plot wind power curves based on measured wind speed and power output. ThisMeanwhile, the wind speed at that time is the wind speed measured by the anemometer on the back of the wind wheel. as the speed and power of the incoming wind. The curve is too high and needs to be corrected. After applying the correction method, the wind energy utilization rate of the horizontal axis will be reduced by 30-50%. Regarding the wind energy utilization rate of small horizontal axis wind turbines, the China Aerodynamic Research and Development Center has conducted relevant wind tunnel experiments, and the measured utilization rate is between 23% and 29%. %.
3. Structural characteristics
During rotation, the blades of the horizontal axis wind turbine are affected by the combined effects of the force of inertia and gravity. The direction of the inertial force changes at. at any time. The direction of gravity remains unchanged, the blade is therefore subjected to an alternating load, which is very detrimentalble to the fatigue resistance of the blade. In addition, horizontal axis generators are placed at an altitude of tens of meters, which brings a lot of inconvenience to the installation, maintenance and inspection of generators.
The blades of the vertical axis wind turbine are much better stressed during rotation than those of the horizontal axis. Since the direction of the force of inertia and gravity always remains unchanged, the blades are subjected to a constant load. The fatigue life is longer than that of horizontal axis wind rotors. At the same time, the vertical axis generator can be placed under the wind wheel or on the ground for easy installation and maintenance.
4. Start-up wind speed
There is a consensus that the start-up performance of horizontal axis wind turbines is good. However, depending on the wind speed of small horizontal axis wind turbines driven. the Re CenterAerodynamic Research and Development of China According to tunnel experiments, the starting wind speed is generally between 4-5 m/s, and the maximum reaches 5.9 m/s. Such startup performance is obviously unsatisfactory. There is also an industry consensus that the starting performance of vertical axis wind turbines is poor, especially for Darrieus Ф-type wind turbines, which have no self-starting capability, which is also a reason which limits the application of the vertical wind turbine. axis wind turbines. but, for the Darrieus type H wind wheel, there is the opposite conclusion. According to the author's research, as long as the aerodynamic profile and installation angle are correctly selected, fairly good starting performance can be achieved. Judging from tunnel experiments, the starting wind speed of this Darrieus-type H-shaped wind rotor has no bonly need 2 m/s. , which is better than the horizontal axis wind turbine mentioned above.