Although the speed of wind power generation is slow, the fans used in wind power generation are very large. This kind of fan can drive a lot of force every time it rotates. So it will generate electricity.
Wind turbines use wind power to rotate machinery, driving the generator rotor and causing the stator to output electrical energy. There are two types of wind turbines, medium-high speed doubly-fed type and low-speed permanent magnet type. The doubly-fed unit is equipped with a gearbox, which can change the speed of the blades from a low speed of more than a dozen turns to a medium-high speed (above a thousand turns). ) to suit the generator to generate electricity.
The low-speed permanent magnet generator can operate at a low speed of more than ten revolutions because of its large number of magnetic poles and the ability to convert low-frequency electrical energy into industrial frequency electrical energy through a frequency converter for utilization. Therefore, although the wind speed is The rotation speed of the blade is very low, but suitable electrical energy can be output and utilized using both mechanical and electrical methods.
In single-phase power, the power of the generator is P=UIcosΦ. In three-phase power, the power of the generator 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, power factor is the ratio of active power to apparent power.
That is, cosΦ=P/S. The 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 the atmosphere, which leads to density differences between the atmospheres. With the assistance of gravity, atmospheric circulation is formed. The flow of gas 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 wind energy into electrical energy.
The principle of wind power generation is actually the same as that of hydropower generation. They convert mechanical energy existing in nature into electrical energy, which is a form that is easy to transport and different from utilization. Of course, it benefits from the discovery of the electromagnetic effect.
The source of mechanical energy is due to the existence of the earth's gravity. Water naturally flows lower. The greater the water drop, the greater the pressure, and the higher the efficiency of driving the generator. However, hydropower generation starts with a water turbine. It is directly impacted by water, and then the water turbine drives the generator.
Reference for the above content: Baidu Encyclopedia - Wind Turbine
The longer the blades increase their weight, the power received will change.
Wind energy refers to the kinetic energy of the wind. The kinetic energy of a specific mass of air can be calculated using the following formula.
Energy = 1/2 X Mass X (Speed)^2
The power of wind blowing through a specific area can be calculated using the following formula.
Power = 1/2 X air density >The unit of air density is kilogram/cubic meter;
The area refers to the cross-sectional area of the air flow, the unit is square meter;
The unit of speed is meter/second.
At sea level and 15 degrees Celsius, the density of dry air is 1.225 kg/m3. Air density changes with air pressure and temperature. As altitude increases, air density decreases.
It can be seen from the above formula that the power of the wind is proportional to the cube (cubic) of the speed and proportional to the swept area of the wind wheel. But in fact, the wind wheel can only extract part of the energy of the wind, not all.
2) The working principle of wind turbines
Modern wind turbines use aerodynamic principles, just like the wings of an airplane. The wind does not "push" the wind wheel blades, but blows through the blades to form a pressure difference between the front and back of the blades. This pressure difference will generate lift, causing the wind wheel to rotate and continuously cross the wind flow.
The rotor of a wind turbine cannot extract all the power of the wind. According to Betz's law, the maximum power that a wind motor can theoretically extract is 59.6% of the wind power. Most wind turbines can only extract 40% or less of the wind's power.
Wind turbines mainly include three parts: wind wheel, nacelle and tower. The most common structure of large-scale wind turbines connected to the power grid is the horizontal-axis three-blade wind turbine.wheel and installed on an upright tubular tower pole.
The wind wheel blades are made of composite materials. Unlike small wind turbines, the rotors of large wind turbines rotate quite slowly. Relatively simple wind turbines use a fixed speed. Usually two different speeds are used - low speed in weak winds and high speed in strong winds. The induction asynchronous generators of these fixed-speed wind turbines can directly generate alternating current at grid frequency.
Relatively new designs are generally variable speed (for example, the V52-850 kilowatt wind motor of Vestas Company has a rotation speed of 14 rpm to 31.4 rpm). With variable speed operation, the aerodynamic efficiency of the wind wheel can be improved, thereby extracting more energy and making less noise in weak wind conditions. Therefore, variable speed wind motor designs are becoming more and more popular than fixed speed wind motors.
The sensors installed on the nacelle detect the wind direction, and through the steering mechanical device, the nacelle and the wind wheel are automatically turned to face the incoming wind.
The rotational motion of the wind wheel is transmitted to the generator in the engine room through the gear transmission (if there is no gear transmission, it is transmitted directly to the generator). In the wind power industry, wind turbines equipped with gearboxes are very common. However, there has also been significant development in multi-pole direct drive generators designed for wind turbines.
Transformers located at the base of the tower (or some located in the engine room) can increase the voltage from the generator to the distribution network voltage (11 kV in Hong Kong).
The power output of all wind turbines varies with the wind. The two most common methods of limiting power output in strong winds (thereby limitingThe pressure that the wind turbine wheel bears is stall adjustment and inclination angle adjustment. Using stall-regulated wind motors, strong winds exceeding the rated wind speed will cause turbulence in the airflow passing through the industrial blades, causing the wind wheel to stall. When the wind is too strong, the tail braking device of the industrial blade will operate to brake the wind wheel. Using a wind motor with angle adjustment, each blade can rotate with the longitudinal axis as the axis, and the blade angle changes with the wind speed, thereby changing the aerodynamic performance of the wind wheel. When the wind is too strong, the blades rotate to the edge of the air facing the incoming wind, thus causing the wind wheel to brake.