Types of wind power plants. Encyclopedia of radio electronics and electrical engineering

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There are many different wind turbines (WPPs), but all of them can be divided into two types: with a horizontal and vertical axis of rotation. The former have a complex structure, but they have a higher utilization rate of wind energy, so they are more often used in industry. The second ones are simpler in design, but less productive. They are rare on the market and are usually used in private homes.

Horizontal (winged) wind turbines

Wind turbines with winged wind wheels and a horizontal axis of rotation have become widespread (Fig. 1). Among them, two- and three-bladed wind turbines have received the greatest development.

Horizontal (vane; WES - bladed mechanisms with a horizontal axis of rotation. The speed of rotation and ease of manufacture have led to the widespread use of vane wind turbines in industry. To ensure maximum rotation speed, the blades of a vane wind generator must be located vertically - perpendicular to the air flow. To achieve this, a special device is used - stabilizer.Horizontal wind farms can be directly connected to the generator without multipliers.Wheel turbine generators have a much higher wind energy utilization factor.At the same time, their rotation speed is inversely proportional to the number of wings.In other words, the smaller the blades, the higher the rotation speed.Therefore, installations with more than three blades are practically not used.

The torque of the wind wheel in them is created by the lifting force formed when the air flow flows around the profile of the blades. As a result, the kinetic energy of the air flow within the area swept by the blades is converted into mechanical energy of rotation of the wind wheel.

The power developed on the axis of the wind wheel is proportional to the square of its diameter and the cube of the wind speed. According to the classical theory of N. E. Zhukovsky, for an ideal wind turbine, the coefficient of wind energy utilization is ξ=0,593. That is, an ideal wind wheel (with an infinite number of blades) can extract 59,3% of the energy passing through its cross section. In reality, in practice, for the best high-speed wheels, the maximum value of the wind energy utilization factor reaches 0,45-0,48, and for low-speed wheels, up to 0,36-0,38. An important characteristic of a wind turbine is its speed, which is the ratio of the speed of the end of the blade to the speed of the wind flow. The end of the blade usually moves in the plane of the wind wheel at a speed that is several times higher than the wind speed. The optimal speed values ​​for a two-blade wheel are 5-7, for a three-blade one - 4-5, for a six-blade one - 2,5-3,5.

Of the design characteristics, the power of a wind wheel is mainly influenced by its diameter, as well as the shape and profile of the blades. Power depends little on the number of blades.

The frequency of rotation of the wind wheel is proportional to the speed and speed of the wind turbine and inversely proportional to the diameter. The height of the center of the wheel also affects the amount of power, since the wind speed depends on the height. The wind turbine power, as noted, is proportional to the wind speed to the third power. At the design wind speed and above, the operation of the wind turbine with rated power is ensured. At wind speeds below the design capacity of the wind turbine can be 20-30% of the nominal or less. Under such operating modes, large energy losses occur in generators due to their low efficiency at low loads, and in asynchronous generators, in addition, large reactive currents occur, which must be compensated. To eliminate this disadvantage, some wind turbines use generators with a rated power of 100 and 20-30% of the rated power of the wind turbine.

In light winds, the generator is switched off first. In some wind turbines, a small generator also provides the ability to operate the installation at low wind speeds at low speeds with a high value of the wind energy utilization coefficient. low power with the help of the tail (tail), in units of small and medium power - by means of the windrose mechanism, and in modern large installations - a special orientation system that receives a control impulse from the wind direction sender (weather vane) installed at the top of the wind turbine gondola.

The windrose mechanism is one or two small wind wheels, the plane of rotation of which is perpendicular to the plane of rotation of the main wheel, working to drive a worm that turns the platform of the wind turbine head until then. until the windroses lie in a plane parallel to the direction of the wind. A winged wind wheel with a horizontal axis of rotation can be located in front of the tower and behind it. In the latter case, the blade is subjected to constant repeated action of variable forces while passing through the shadow of the tower, which at the same time significantly increases the noise level. A number of methods are used to control the power and limit the speed of rotation of the wind wheel, including the rotation of the blades or parts of them around their longitudinal axis, as well as flaps, valves on the blades, and other methods.

The main advantages of wind turbines with a horizontal axis of rotation of the wind wheel is that the conditions for the air flow around the blades are constant, do not change when the wind wheel turns, but are determined only by the wind speed. Due to this, as well as a fairly high value of the coefficient of wind energy utilization. Wing-type wind turbines are currently the most widely used.

Vertical (rotor) wind turbines

Another type of wind turbine is the Savonius rotor (Fig. 2). Torque occurs when air flows around the rotor due to the different resistance of the convex and concave parts of the rotor. The wheel is simple, but has a very low wind energy utilization factor - only 0,10-0,15. In recent years, in a number of foreign countries, especially in Canada, they began to develop a wind turbine with a Darrieus rotor, proposed in France in 1920. This rotor has a vertical axis of rotation and consists of two to four curved blades. The blades form a spatial structure that rotates under the action of lifting forces. arising on the blades from the wind flow. In the Darrieus rotor, the coefficient of wind energy utilization reaches 0,30-0,35. Recently, the development of the Darrieus rotary engine with straight blades has been carried out.

The main advantage of Darrieus wind turbines is that they do not need a wind-orientation mechanism. They have a generator and other mechanisms placed at a slight height near the base. All this greatly simplifies the design. However, a serious organic drawback of these wind turbines is a significant change in the conditions of the flow around the wing during one revolution of the rotor, which is cyclically repeated during operation. This can cause fatigue phenomena and lead to the destruction of the rotor elements and serious accidents, which should be taken into account when designing the rotor (especially at high power wind turbines). In addition, to get started, they need to be untwisted.

Vertical (carousel, rotary) wind farms are bladed mechanisms with a vertical axis of rotation. They operate at low wind speeds, but have low efficiency. Therefore, they are quite rare and are used, as a rule, in home systems. At the same time, unlike horizontal ones, they can operate in any wind direction without changing their position. The installation itself monitors "where the wind is blowing from", therefore, it does not need any additional devices. Rotary wind turbines are low-speed, which makes it possible to use simple electrical circuits in them to collect energy, in particular, asynchronous generators. At the same time, slow speed limits the use of vertical wind farms, as it forces the use of step-up gearboxes - multipliers with a very low efficiency. It is problematic to operate such an installation without a multiplier.

Fig.2. Savonius rotor: a) two-bladed, b) four-bladed

Dependencies of wind power utilization factor ξ, from speed Z for various types of wind turbines are shown in Fig.3. It can be seen that two- and three-blade wheels with a horizontal axis of rotation have the highest value of E. For them high ξ is preserved in a wide range of speed Z. The latter is essential, since wind turbines have to operate at wind speeds that vary within wide limits. That is why installations of this type have received the greatest distribution in recent years.

Fig.3. Typical dependences of wind power utilization factor ξ, on the speed of the wind wheel Z: 1 - an ideal winged wind wheel; 2, 3 and 4 - two-, three- and multi-bladed impeller wind turbines; 5 - Darrieus rotor; 6 - Savonius rotor; 7 - four-blade wind wheel of a Danish mill.

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