Wind power systems for heat supply of settlements: Wind turbines

The wind power turbine (fig. 4.9 and 4.10) consists of towers, turbine, transmissions and electrical generator. Its work principle is based on converting of the kinetic energy of moving air into kinetic mechanical energy of a bulky rotating element – wind turbine. Rotary motion of the turbine by means of transmission is converted into rotational kinetic energy of the electrical generator rotor. Electrical generator rotor consists of conductor windings. At motion in a magnetic field of permanent or electrical magnets, conductors create electric current. Further parameters of electric current are transforming to values, suitable for consumption (heating, lighting, powering household devices and industrial equipment). The multiple blades WPTs are less effective, as the blades hinder one to other. At the same time the turbines with two and three blades work effectively at large speeds of rotation when they maximally use wind stream that comes through the area of rotor.

Velocity of wind is the most essential factor stipulating electrical power produced by wind turbine. When speed of wind increases the masses of air, that pass through the cross section of rotor blades of turbine is also increased. Energy of wind changes proportionally to the cube of wind speed. Energy of air flow can be calculated in accordance with following expression:

 

E = 0,5ρAv3.    

where ρ = 1,226 kg/m3 – density of air, A – area of cross section of the rotor blades, v - speed of wind in m/s. The greater is area of rotor, the more energy wind turbine produces.

From the other hand kinetic energy of the moving air is proportional to the mass and density of this air. The density of the air relies on the amount of molecules in a unity of volume. At normal atmospheric pressure and temperature 150ะก the density of the air is 1226 kg/m3, but with the increase of humidity the density of air goes down. That why in winter the air has greater density and wind turbine produces more energy than in summer, at identical speed of wind. On the territory, located above a sea level, for example in mountains, atmospheric pressure is less, accordingly, a density of air is also smaller.

The land relief, forests and buildings cause the decreasing of wind speed and contribute to its turbulence. At removal from the Earth's surface the air streams grow, at an altitude of 1 km above the Earth the terrain almost does not affect the velocity of the wind. Wind territories, located in the vicinity of airports or lakes are favorable for wind turbine installation.

When designing wind turbines it is necessary to take into account the different impact of the wind force on the top and bottom blades. Asymmetry of power can lead for destruction of the turbine.

The turbine blade angle relatively air flow may be constant or adjustable, providing optimum performance of the wind turbine. The adjustable angle blades use energy of the wind more effectively and therefore produce more electrical power. The turbines with tightly anchored blades are simpler to maintain, but their effectiveness is lower. The turbine blades are making from the fiberglass, polystyrene, epoxy polymer or carbon plastic. The blade length of today’s WPTs changes within 25…70 m.

 

By Vasil Sidorov on October 10, 2012 

Technopark QUELTA, Queltanews from

Nizhyn Laboratories of Scanning Devices

sidorovvasil@gmail.com

 


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