Slide 1

S.E. Electrical Engineering UNIT IV Wind Energy System

Slide 2

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

Slide 3

Slide 4

Leading Manufacturers of Wind Turbine 1.Vestas (Denmark) - 35,000 MW 2.Enercon (Germany) - 19,000 MW 3.Gamesa (Spain) 16,000 MW 4.General Electric (USA, Germany) 15,000 MW 5.Siemens (Denmark, Germany) 8,800 MW 6.Suzlon (India) 6,000 MW 7.Nordex (Germany) 5,400 MW 8.Acciona (spain) 4,300 MW 9.Repower (Germany) 3,000 MW 10.Goldwind (china) 2,889 MW Source: Wikipedia

Slide 5

Wind Power Density of India

Slide 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.

Slide 7

State wise potential in India, 2005

Slide 8

Advantages and Disadvantages 1. Advantages :- 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

Slide 9

2. 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.

Slide 10

Classification of wind Planetary winds :- are caused due to greater solar heating of the earths 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.

Slide 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.

Slide 12

Site selection Four types of site are suitable for Wind Energy Conversion System (WECS) 1. Plane land sites 2. Hill tops sites 3. Sea-shore sites 4. Off-shore shallow water sites

Slide 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.

Slide 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.

Slide 15

Slide 16

Classification of Wind Mills :- Based on Orientation of the Axis of Rotor :- 1. Horizontal axis 2. Vertical axis Based on Type of Rotor :- Propeller type (Horizontal axis) Multiple Blade type (Horizontal axis) Savonius type (Vertical axis) Darrieus type (Vertical axis)

Slide 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 300-400 rpm. For multi blade type range 60-80 rpm. Material used for blades is glass fibre reinforced plastic.

Slide 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 12- 20, inner and outer end are fixed. Diameter varies 2 m to 5 m.

Slide 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.

Slide 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.

Slide 21

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

Slide 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.

Slide 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.

Slide 24

Horizontal Axis Wind Turbines generator Vertical Axis Wind Turbines generator

Slide 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.

Slide 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.

Slide 27

Types of Wind Turbine Generator Technologies Presently four major types of WTG Technologies used: 1. Squirrel Cage Induction Generators driven by fixed-speed, stall-regulated wind turbines 2. Induction Generators with variable external rotor resistance driven by a variable-speed, pitch regulated wind turbines 3. Doubly-Fed Induction Generators driven by variable-speed, pitch regulated wind turbines 4. Synchronous or Induction Generators with full converter interface (back-to-back frequency converter), driven by variable-speed, pitch regulated wind turbines

Slide 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

Slide 29

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

Slide 30

Tip-Speed Ratio 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 V TSR = Where, = rotational speed in radians /sec R = Rotor Radius V = Wind Free Stream Velocity R R

Slide 31

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

Slide 32

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

Slide 33

Dependence of Solidity , on Tip Speed ratio 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.

Slide 34

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

Slide 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.

Slide 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.

Slide 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.

Slide 38

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

Slide 39

Grid connected wind energy conversion system

Slide 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.

Slide 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.

Slide 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.

Slide 43

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

Slide 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.

Slide 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.