Wind is a natural phenomenon caused by air movement, which is caused by solar radiation heat. Sunlight shines on the surface of the earth, causing the surface temperature to rise. The air on the surface expands due to heat and becomes lighter and rises. After the hot air rises, low-temperature cold air flows in laterally. The rising air gradually cools and becomes heavier and falls. The higher surface temperature heats the air and causes it to rise. This flow of air creates wind.
Extended informationWind speed is sometimes expressed by pressure, which is called wind pressure. If V is used to represent the wind speed (m/s), P is perpendicular to the direction of the wind, and the wind pressure kg/m2 on an area of 1m2, the relationship is P=0.125V2.
Wind direction refers to the direction of airflow, and is often recorded in 16 directions. Wind speed is the horizontal distance that air moves per unit time, measured in meters per second. The horizontal wind speed in the atmosphere is generally 1.0 to 10 meters/second, and typhoons and tornadoes sometimes reach 102 meters/second. The wind speed in farmland can be less than 0.1 meters/second. There are two types of wind speed observation data: instantaneous value and average value. Generally, the average value is used. Wind is measured using instruments such as electric anemometers, portable anemometers, dyne anemometers, and thermometers used to measure breezes in farmland. It can also be estimated based on the wind force level table based on the signs of ground objects.
Reference wind (natural phenomenon) Baidu Encyclopedia
Why do wind turbines only have three blades? Isn’t the more blades the better?
KVA represents the transformer capacity, and KW represents the power.
KVA is used to represent apparent power, that is, the capacity of the equipment, and KW is used to represent active power. The relationship between apparent power and active power is: active power = apparent power × power factor (power factor is less than 1) That is, the value of active power is generally smaller than the value of apparent power.
In DC: current multiplied by voltage is active power, there is no term for apparent power.
In AC: the voltage multiplied by the current is the active power, the dimension is W; the voltage cross multiplied by the current is the reactive power, the dimension is Var; the voltage effective value multiplied by the current effective value is the apparent power, The dimension is VA.
Active power is eventually converted into various energies and dissipated, such as mechanical energy and thermal energy; while reactive power is exchanged between inductors and capacitors and ideally will not be consumed itself.
The relationship between active power P, reactive power Q and apparent power S: P=S×cosΦ (cosΦ is the power factor)
For example: power factor cosΦ=0.8 active power is P=1kW.
Then tanΦ=0.75, so the square of the apparent power S = the square of P + the square of P*tanΦ.
That is, S=1.25kVA.
When the power factor is 1, 1kVA=1kW.
Extended information:
Electrical power:
A term in physics, the work done by electric current per unit time is called electrical power. It is a physical quantity used to express the speed of consuming electrical energy. It is represented by P. Its unit is Watt (Watt), referred to as "Watt", and its symbol is W.
As a physical quantity that represents the speed of current doing work, the power of an electrical appliance is numerically equal to the electrical energy it consumes in 1 second. If the electrical energy "W" (SI unit is J) is consumed in such a long period of time as "t" (SI unit is s), then the electrical power of this electrical appliance is P=W/t (definition formula). The electrical power is equal to both ends of the conductor The product of voltage and current through a conductor.
(P=U·I). For purely resistive circuits, the formulas P=I^2*R and P=U^2/R can also be used to calculate the electrical power.
Each electrical appliance has a normal working voltage called rated voltage. The power of the electrical appliance that works normally at the rated voltage is called the rated power. The power of the electrical appliance that works at the actual voltage is called the actual power.
Reference materials:
Baidu Encyclopedia-kw
Experts question tunnel wind power generation
With the development of the times, the functions of these machines and equipment have also been continuously upgraded. , grain milling, water transportation, power generation, etc. Traditional wind turbines come in a variety of shapes and designs, but they are all currently being replaced by the same design. As a clean and renewable new energy, wind energy has gained great popularity in recent years. When you are walking near the wind turbine and admiring the sight of the wind leaves turning leisurely under the blue sky and white clouds, are you also curious about the difference between the 3 leaves and the 5 leaves of the wind turbine?
As a clean and renewable new energy, wind energy has received great attention in recent years. When you are walking near the wind turbine and admiring the sight of the wind leaves turning leisurely under the blue sky and white clouds, are you also curious about the difference between the 3 leaves and the 5 leaves of the wind turbine?
To put it simply, three leaves are easy to balance. Too many leaves are difficult to balance and the cost is high.
At rated wind speed, the generated power is proportional to the swept area of the wind rotor, that is, a wind rotor with 200 blades and a wind rotor with 1 blade can produce the same power.
It can be seen from the above figure that as the number of blades increases, the wind energy utilization coefficient also increases, but in the process from 3 blades to 4 blades to 5 blades, the wind energy utilization coefficient increases by a large margin , compared with the increase from 1 leaf to 2 leaves to 3 leaves, the increase is much smaller. From a cost perspective, the gain outweighs the loss.
So, the fewer blades of a wind turbine, the better?
First of all, the advantage of multiple blades is the larger torque conversion rate, but in terms of energy conversion rate, the 4-leaf and 5-leafThe efficiency is lower than that of a 3-blade fan.
The main reason is that the large resistance of multi-blade fans causes a considerable amount of turbulence that interferes with the rotation of the blades, thus reducing the energy conversion rate.
So it is much better to choose 3 leaves than 4 or 5 leaves. (Well, the same is true for electric fans); Secondly, too few blades will affect power generation efficiency.
In fact, there is currently a patent in Europe that has two leaves, placed vertically, which can double the efficiency! However, the 2-blade wheel hub has a special structure with a seesaw structure, and the fatigue problem is worse than that of the 3-blade wheel.
Moreover, the fewer blades, the higher the rated speed. When the speed is high to a certain extent, the circumferential linear speed of the blade tip is very large, causing large wind resistance. The drag torque limits the further increase in power generation power and speed. Therefore, it is not good to have too few blades. Three blades are mainly for good balance and low cost. After a long period of verification, they have become a common fan form today.
The idea of "using subway tunnel wind energy to generate electricity" has aroused the curiosity of many people and also attracted some doubts. “Although from the perspective of effective energy utilization, the wind energy generated in the subway system can be used for development and utilization, the wind energy generated is too small and it is difficult to achieve economies of scale, which does not have economic value in development. "Zhou Tao, a new energy industry analyst at Great Wall Securities, believes that currently, he has not heard of the practice of using wind energy in the city to generate electricity worldwide. Even if the subway company agrees to develop such a project, it will be difficult to attract the interest of investors.
Wang Mengshu, an academician of the Chinese Academy of Engineering, is also not optimistic about this project. He believes that the idea of using wind energy in tunnels to generate electricity is simply impossible and technically unreliable. He said that trains running on metro lines have time intervals. At present, Beijing's fastest Line 1 generally has an interval of more than 2 minutes. As a result, even if a small wind turbine is installed in the tunnel, it cannot obtain sustained and stable wind power.
Since the two parallel subway tunnels are every 400 to 500 meters, they are connected by passages in the middle. In such two tunnels, the wind generated by the subway train passing through will enter the other tunnel. In addition, the trains in the two tunnels run in different directions, so the directions of the wind are also different. Therefore, it is difficult for wind power equipment to operate continuously and stably.
In response to experts’ doubts, Zhong Yan said that in some actual tests they conducted, they have not yet found the problems caused by the wind direction of the tunnel mentioned by Academician Wang Mengshu. In response to the questions raised by the experts, they also wanted to communicate with relevant experts including Academician Wang. For safety, they have considered designing the wind rotors mounted on both sides of the subway tunnel into slender cylindrical wind rotors.
Have you considered the wind tunnel principle for tunnel power generation? The operation of the subway requires the excess air in front to be pushed to the back of the car as quickly as possible. In this way, the locomotive can operate with minimum energy consumption. Adding some wind blocking facilities around the tunnel will definitely affect the speed and energy consumption of the locomotive. Adding some wind turbines around the tunnel will increase theThe windward area of the front of the locomotive is increased. Increase wind resistance.