1. Subject: Power Generation Technologies
S.E. Electrical Engineering
UNIT IV
Wind Energy System

2. Introduction
Wind is an indirect form of solar energy since wind is introduced chiefly by the uneven heating of the earth’s crust by sun.
Conversion of this wind energy into electrical energy can reduce the power deficit .

3. World wide wind generating capacity is less than 5000 MW in 1995 and is 39000MW in 2003, an increase of nearly eight fold.

4. Leading Manufacturers of Wind Turbine
Vestas (Denmark) - 35,000 MW
Enercon (Germany) - 19,000 MW
Gamesa (Spain) – 16,000 MW
General Electric (USA, Germany) – 15,000 MW
Siemens (Denmark, Germany) – 8,800 MW
Suzlon (India) – 6,000 MW
Nordex (Germany) – 5,400 MW
Acciona (spain) – 4,300 MW
Repower (Germany) – 3,000 MW
Goldwind (china) – 2,889 MW
Source: Wikipedia

5. Wind Power Density of India

6. Wind Energy It is estimated that India has potential about 20000 MW.
There are various wind potential stations are identified :
Tamilnadu-39, Gujrat-36, AP-30, Maharashtra-27, Karnataka-26, Kerala-16, Lakshadweep-8, Rajasthan-8, MP-7, Orisa-7, WB-2 and 1 each in Anadman and UP
Out of 208 stations 7 stations have shown wind power density more than 500W/sq.m.

7. State wise potential in India, 2005

8. Advantages and Disadvantages
It is available free and is inexhaustible.
It is clean and non – polluting.
Have low maintenance cost.
Has low cost of power generation of about Rs. 2.25/kWh

9. Disadvantages
Capital cost is high.
Wind energy available in fluctuating in nature.
Large variation in wind during cyclones, tornadoes may cause damage to installation.
Design of system is difficult due to large variation in wind speed.
It causes sound pollution in large unit.

10. Classification of wind
Planetary winds :- are caused due to greater solar heating of the earth’s surface near the equator as compared to solar heating near to poles.
Local winds :- are caused due to differential heating of land and water in costal areas.

11. Principle Of Wind Power Generation
Total wind power is proportional to the cube of incoming wind velocity, density of air and the cross – sectional area of wind stream.
Total wind power density- it is defined as the total wind power per unit area of wind stream.

12. Site selection
Four types of site are suitable for Wind Energy Conversion System (WECS)
Plane land sites
Hill tops sites
Sea-shore sites
Off-shore shallow water sites

13. Some important criteria for site selection
Located where the high avg. wind velocities available are in the range of 6 m/s to 30 m/s through out the year.
The WECS must be located far away from cities and forests. There should no tall structures in 3 km radius.
The wind farms are located in flat open areas, deserts, seas, shores and off shores sites since wind velocities are high in these location.
Wind velocity of wind must measures at different heights, as height increases wind velocity increases. This helps in selection of appropriate height of wind tower.

14. Some important criteria for site selection
Historical data of wind mean speed must be collected for avg. velocities during the year for proper selection of the site.
Ground surface should have high soil strength to reduce cost of foundation.
Transportation facilities should be constructed for site.

16. Classification of Wind Mills :-
Based on Orientation of the Axis of Rotor :-
Horizontal axis
Vertical axis
Based on Type of Rotor :-
Propeller type (Horizontal axis)
Multiple Blade type (Horizontal axis)
Savonius type (Vertical axis)
Darrieus type (Vertical axis)

17. Horizontal Axis Wind Mill :-
Horizontal wind mills may be type Propeller or multi- bladed.
The orientation of the axis of rotors are along the horizontal axis , so that it is parallel to the direction of wind stream.
Most commonly used wind mills are propeller type.
Single bladed, Two bladed and Three bladed.
Two bladed – 2 MW to 3 MW capacity.
Three bladed – 3 MW to 15 MW capacity.
The rotational speed range rpm.
For multi blade type range rpm.
Material used for blades is glass fibre reinforced plastic.

18. Horizontal Axis Wind Mill :-
Multiblade rotor consist of number of curved sheet metal blades with increasing chord length away from the centre.
No of blades used , inner and outer end are fixed.
Diameter varies 2 m to 5 m.

19. Vertical Axis Wind Mill :-
Savonius rotor, a hollow elliptical cylinder is sliced into two pieces and each of these halves fixed to a vertical axis with a fixed gap.
It forms S – shape due to this it is also called as S-rotor.
Darrieus rotor consists of two or three convex blades with aerofoil cross-section.
Along length blades are curved into shape called troposkein.
The blades are mounted symmetrically vertical.

20. Vertical Axis Wind Mill :-
Advantage of this type of mill is no orientation of vanes of the mill is required according to direction of wind.
Can generate power with any direction.
No requirement of tall structure.
Low cut in speed as compare to horizontal axis mill.
8 kmph in vertical and 16 kmph in horizontal.

21. Wind Turbine Configurations
HAWT
VAWT
Boyle, G., Renewable Energy, 2nd ed., Oxford University Press, 2004 21

22. Horizontal Axis Wind Generator :-
Used all over the world.
The main component are
Usually have two or three blades.
Diameter of rotor 2 m-25 m.
Mounted on tower top, designed to with stand with wind load during abnormal condition.
Electromagnetic breaks are provided for automatic application of break if wind speed exceed the designed speed.
The hub, breaks, gear box generator with electrical controls are housed in box called nacelle.

23. Horizontal Axis Wind Generator :-
A yaw control mechanism is provided to adjust the nacelle around vertical axis.
In small wind turbines, a flap or vanes is provided on the nacelle for automatic moving according to direction of wind
Generator provided for generation of power.

24. Horizontal Axis Wind Turbines generator
Vertical Axis Wind Turbines generator

25. Vertical axis wind turbine generator
It consist of hollow vertical shaft mounted between the top and bottom bearings.
The tower height about 100 m.
Two thin and curved symmetrical blades are attached at the rotor shaft at the top and bottom.
The turbine shaft coupled to the generator having in between breaks, gear box and electrical control.

26. Vertical axis wind turbine generator
It does not need any yaw control mechanism, mill can accept wind from any direction.
It does not need to support the nacelle on the top of tower, since gear box, breaks, generator on ground.
Overall cost is less.
Maintenance cost is low.
Design is easier.

27. Types of Wind Turbine Generator Technologies
Presently four major types of WTG Technologies used:
Squirrel Cage Induction Generators driven by fixed-speed, stall-regulated wind turbines
Induction Generators with variable external rotor resistance driven by a variable-speed, pitch regulated wind turbines
Doubly-Fed Induction Generators driven by variable-speed, pitch regulated wind turbines
Synchronous or Induction Generators with full converter interface (back-to-back frequency converter), driven by variable-speed, pitch regulated wind turbines

28. Doubly Fed Induction Generator (DFIG)
Wound rotor induction generator with slip rings
Rotor is fed from a three-phase variable frequency source, thus allowing variable speed operation
reduction of mechanical stress; higher overall efficiency, reduced acoustical noise
The variable frequency supply to rotor is attained through the use of two voltage-source converters linked via a capacitor
Note: A more appropriate designation for this type of generator is: Doubly Fed Asynchronous Generator

29. Performance of wind mills Power coefficient Cp
The coefficient of performance, Cp is defined as ratio of power, P delivered by the rotor to the maximum power, Pmax i.e coefficient of performance of wind turbine.

30. Tip-Speed Ratio ΩR TSR = V
Tip-speed ratio is the ratio of the speed of the rotating blade tip to the speed of the free stream wind.
There is an optimum angle of attack which creates the highest lift to drag ratio.
Because angle of attack is dependant on wind speed, there is an optimum tip-speed ratio R ΩR V
TSR =
Where,
Ω = rotational speed in radians /sec
R = Rotor Radius
V = Wind “Free Stream” Velocity

31. Solidity, ϒ
Ratio of the blade area to the swept frontal area of wind turbine.
For vertical axis

32. Dependence of power coefficient, Cp on Tip Speed ratio, λ
Each type of wind mill has some optimum tip speed to wind speed ratio, λ at which it gives maximum Cp.
Cp is lowest for Savonius and Dutch of blades.
Cp is maximum for propeller type of blades.
Ideal value of Cp is about 0.59.

33. Dependence of Solidity ‘ϒ’, on Tip Speed ratio ‘λ’
Rotor with high tip speed ratio have low value of solidity. Rotors turn at high speed.
Rotor with tip low speed ratio have low value of solidity. Rotors turn at low speed.
The torque generated by Propeller and Darrieus type of rotor is low , therefore they are suitable for electrical power generation.
The torque generated by multi bladed and Savonius type of rotor is high , therefore they are suitable for application like pumping of water .

34. Methods of overcoming Fluctuation of power
Pitch control.
Passive stall control.
Active stall control.
Yaw control.

35. Pitch control :-
The power output continuously checked by electronic measuring unit.
When power output becomes high, it actuates the blade pitch mechanism which turns the blades out of wind.
This reduces the power output.
When wind velocity reduces and power falls, the blade is turned back to the original position and power increases.

36. Passive stall control
In this control the blade is fixed at a fix angle.
When increase it creates the turbulence on the side opposite to that facing the wind reduces the angle of attack.
This will reduces the lift force developed and hence reduces the power.
Simpler than pitch control.

37. Active stall control
There are two blades with changeable pitch angles.
When the wind speed reduces, it pitches the blades, so that wind power output increases.
When power reaches the rated power, the blade is pitched in opposite direction to that of pitch control.

38. Yaw control
Turbine rotates about vertical axis facing or away from the wind
Used only in small turbine

39. Grid connected wind energy conversion system

40. Constant Speed drive
DC generator :- A permanent magnet type dc generator is used for small and medium power generation upto 100kW .
Synchronous generators :- are used for medium and large power generation having constant speed with ±1% speed fluctuation.
Induction generators :- are used for variable shaft speed upto 10% . These are preferred because of low cost.

41. Variable Speed Drive Scheme
Variable voltage and Variable frequency output of synchronous or induction generator converted into DC by converter and then into fixed voltage and fixed frequency AC by using inverter.

42. Wind Energy conversion system for battery charging
Wind energy converted into DC by DC generator and Charges the batteries.
Charge controller is used to control the charging and discharging.
Can be used as standalone system.

43. Stand alone system with AC –DC load
Can be supply power AC as well as DC.
Needs inverter to converter DC to AC.

44. Wind Energy direct and indirect effect
Indirectly the CO2 and other emissions are released during the course of their construction. But very negligible amount as compared to fossil fuel power plant.
It causes noise pollution. For this wind mills located at least 2 to 3 km away from city.
It poses threat to bird life due to collision of birds with blades or wind tower.
Mechanical failure of wind mill may cause its parts to fly and harm the people working around them.

45. Wind Energy direct and indirect effect
Electromagnetic waves of TV signals are obstructed by wind turbines. It may causes the poor quality of radio and TV.
Ecosystem is affected by the use of large scale wind generators since, the nearby lakes and rivers will becomes warmer caused by reduced evaporation from their surface.