Classification of wind turbines and their respective characteristics
The wind turbine consists mainly of two major components:
Wind turbine part - it converts wind energy into mechanical energy;
The generator part - it converts mechanical energy into electrical energy.
Wind turbines can be classified into many different types depending on the type of structure used by the two major fans and the different features of their respective technical solutions, plus their different combinations.
(1) If the direction of the main shaft of the fan is rotated (ie, the relative position of the main shaft and the ground), it can be divided into:
“Horizontal axis fan” – the rotating shaft is parallel to the ground, and the impeller needs to adjust position with the wind direction;
"Vertical Axis Fan" - The rotating shaft is perpendicular to the ground. The design is simple. The impeller does not have to adjust direction as the wind direction changes.
CNWPEM.COM (2) can be divided into "lifting type fan" or "resistance type fan" according to the blade force.
(3) According to the number of blades, it can be divided into "single blade", "double blade", "three blade" and "multi blade" type fan; the number of blades is determined by many factors, including aerodynamic efficiency, complexity, Cost, noise, aesthetic requirements, etc.
Large wind turbines can consist of 1, 2 or 3 blades.
Wind turbines with fewer blades usually require higher rotational speeds to extract energy from the wind, so the noise is greater. And if there are too many blades, they interact to reduce system efficiency. At present, 3-blade wind turbines are the mainstream. From an aesthetic point of view, the 3-blade wind turbine looks balanced and beautiful.
(4) According to the direction of the wind received by the fan, there is an “upward wind direction”—the front of the impeller faces the wind direction (ie, the wind is rotating in front of the tower) and the “downwind direction”—the impeller follows the wind direction, two Types.
Upwind fans generally require some sort of steering device to keep the impeller facing the wind.
The downwind fan automatically aligns with the wind direction, eliminating the need for a steering device. However, for the downwind fan, since a part of the air passes through the tower and then blows toward the impeller, the tower interferes with the airflow flowing through the blade to form a so-called tower shadow effect, which degrades performance.
(5) According to the different mechanical connection modes of power transmission, it can be divided into “fighting gear type fan” and “direct drive type fan” without gear box.
The blade of the gear box type fan transmits the torque to the transmission shaft of the generator through the gear box and its high speed shaft and universal elastic coupling. The coupling has good absorption damping and vibration characteristics, and can absorb an appropriate amount. Radial, axial and angular offset, and the coupling prevents overloading of the mechanism.
The direct drive type fan has a different path. In combination with a number of advanced technologies, the torque of the blade can be directly transmitted to the drive shaft of the generator without increasing the speed of the gear box, so that the electric energy generated by the fan can also be connected to the grid. This design simplifies the structure of the device, reduces the probability of failure, and has many advantages. It is now used on large units.
(6) According to the power adjustment method of receiving wind energy by the blade, it can be divided into:
"Fixed pitch (stall type) unit" - the connection between the blade and the hub is fixed. When the wind speed changes, the windward angle of the blade cannot change. Due to its simple structure and reliable performance, the fixed pitch (stall type) unit has always dominated the development and utilization of wind energy in the past 20 years.
"Pitching unit" - the blade can rotate around the central axis of the blade, so that the blade angle of attack can be adjusted within a certain range (generally 0-90 degrees), and its performance is much improved compared with the fixed pitch type, but the structure also tends to Complex, now used on large units.
(7) According to whether the impeller speed is constant, it can be divided into:
"Constant speed wind turbine" - simple and reliable design, low cost, low maintenance, direct grid connection; shortcomings: low aerodynamic efficiency, high structural load, causing grid fluctuations to the grid, and absorbing reactive power from the grid.
“Variable wind turbines” – high aerodynamic efficiency, low mechanical stress, low power fluctuations, high cost efficiency and light support structure. The disadvantage is that the power is sensitive to voltage drop, the price of electrical equipment is high, and the maintenance is large. It is now commonly used in large-capacity main models.
(8) According to the classification of generator types of wind turbines, they can be divided into two categories:
"Asynchronous generator type" "synchronous generator type"
They can be used for variable speed operation of the fan as long as the appropriate converter is used.
