Wind results from air in motion. Air in motion arises from a pressure gradient. Wind can be proadly classified as "planetary" & "local". Planetary winds are caused by greater solar heating of the earth`s surface near the equator than near the northern or southern poles. This cause warm tropical air to rise and flow through the upper atmosphere towards the poles & cold air from the poles to flow back to the equator nearer to earth's surface.
The direction of motion of planetary winds with respect to the earth is affected by the rotation of the earth. The wam air moving toward the poles in the upper atmosphere assumes an easterly direction that results in prevailing westerlies. The westerlies controls events between the 30 0 & 60 0 latitudes. Because the earth`s axis is inclined to its orbital plane around the sun.
Local winds are caused by two mechanisms. The first is differential heating of land & water. So far insulation during the day is readily converted to sensible energy of the land surface but is partly absorbed in layers below the water surface and partly consumed in evaporating some of that water.
This is the mechanism of shore breezes. At night, the direction of the breezes is reversed because the land mass cods to the sky more rapidly than the water assuming the clear sky. The second mechanism of local wind is caused by bills & mountain sides.
The air above the slop side heats up during the days & cools down at night, move rapidly than the air above the low lands. This causes heated air during the day to rise along the slopes & relatively cool heavy air to flow down at night.
Basic components of WECS
Aero turbine :- Aero turbine converts energy in moving air to rotary mechanical energy in general, they required pitch control & yow control for proper operation. A mechanical interface consisting of step up gear & a suitable coupling transmits the rotary mechanical energy to an electrical generator.
Yaw control :- for localities with the prevailing wind in one direction, the design of turbine can be greatly simplified. The rotor can be in a fixed orientation with the swept area perpendicular to the predominant wind direction. The purpose of the Controller is to sense wind speed, wind direction, shafts speeds & torque at one or more points, o/p power & generator temperature as necessary.
Rotors :- Rotors are mainly of two types.
• Horizontal axis rotor.
• Vertical axis rotor.
One advantages of vertical axis machines is that they operate in all wind direction & thus need no yaw adjustment. The rotor is only one of the important components for an effective utilization, all the components needs to be designed & matched with the rest of the component.
The windmill head :- they supports the rotor, housing the rotor bearing. It also houses any control mechanism incorporated like changing the pitch of the blades for safety devices & tail Vane to orient the rotor to face the wind.
Generator :- Among the constant speed generator candidates for use are synchronous induction & permanent magnet type. The generators of choice is the synchronous unit for large aero generator system because it is very versatile & has an extensive data base.
Controls :- Controls system performs the following function.
1. the orientation of the rotor into the wind ( azimuth of yaw );
2. start up and cut-in of the equipment;
3. power control of the rotor by varying the pitch of the bladws;