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Wind turbine (bhaw nath jha)


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Wind turbine (bhaw nath jha)

  1. 1. Presentation on WIND TURBINE BY BHAW NATH JHA 069/MSR/503
  2. 2. Introduction Concept  Wind energy is a form of solar energy. Sun alleviates the atmospheric temperature and pressure difference is produced due to uneven solar heating of the earth’s surface.  While the sun heats air , water and land on one side of the earth , the other side is cooled by thermal radiation .
  3. 3.  Much more solar energy is absorbed near the equator than at the poles .  Warmer , lighter air rises at the equator and flows towards the poles , while cooler heavier air returns from the poles to replace it.
  4. 4. Wind power 2 2 1 V VolumeUnit EnergyKinetic The volume of air that passes through an imaginary surface : tVAVolume tAVEnergyAvailable 3 2 1 AVPowerAvailable 3 2 1 Both energy and power are proportional to the cube of the wind speed.
  5. 5. AVPowerExtracted 3 2 1 Air density ‘ρ’ can be calculated by Z*)10 4*194.1(225.1 z = the location's elevation above sea level in meter Value of “η” commonly ranges from 0.10 to 0.50.
  6. 6. Wind speed variation with height Heightabovegroundz Wind speed uz z 0 d Approximate scale of local obstructions z0 - the roughness length d - zero plane displacement
  7. 7. WIND MACHINE CHARACTERISTICS  Three factors determine the output of a wind machine. They are: 1. the wind speed 2. the cross-section of the wind swept by rotor 3. the overall conversion efficiency of the rotor, transmission system and generator of pump
  8. 8. Contd...  K.E. of wind = ½ mV2 But, m = AV K.E. = ½ AV3  The available wind energy is directly proportional to the cube of the wind speed.  Since A = /4 D2, the energy is proportional to the square of the diameter of the rotor.  Hence higher the wind speed and diameter higher is the efficiency.  The relation can also be seen from the graph in next slide.
  9. 9. Dependence of wind rotor power on wind speed and rotor diamete
  10. 10. Types of wind turbine 1. Horizontal Axis Wind turbine (HAWT) 2. Vertical Axis Wind Turbine (VAWT) HAWT VAWT
  11. 11.  Vertical axis machines are of simple design as compared to the horizontal axis type.  Horizontal axis wind machines are further classified as single bladed,multibladed and by- cycle multiblades types.  Vertical axis wind machines are sub divided into Savonious (low velocity wind) and Darrieus(high velocity wind) based on the working speed and the velocity required by the machine for operation.
  12. 12. SAVONIUS ROTOR  One of the simplest of the modern types of wind energy conversion system. (work likes a cup anemometer)  Invented by S.J Savonius in the year 1920 and has become popular since it requires relatively low velocity winds for operation.  It consists of two half cylinders facing opposite directions in such a way that as to have almost an S- shaped cross section and is mounted on a vertical axis perpendicular to the wind direction with a gap at the axis between the two drums.
  13. 13. DARRIEUS ROTOR  Invented originally and patented in 1925 by G.J.M. Darrieus,a French engineer.  It is a vertical axis machine with a modern rotating propeller type windmill, by use of an efficient airfoil, effectively intercepts large area of wind with a small blade area.  It has two or three,curved(egg beater) blades with airfoil cross section and constant chord length. Both ends of blades are attached to a vertical shaft.
  14. 14. Multi blade wind rotor  As name suggests, it contains a number of wind blades.  It has higher torque coefficient and lower power coefficient  Due to high starting torque they are more suitable for pumping water.  It is rarely used in electricity generation due to low speed.  If to be used gear reduction becomes a must to increase speed
  15. 15. HAWT Advantages Disadvantages  High wind speeds  High efficiency  Less aerodynamic losses  Less starting difficulties  Lower cut-in wind speeds  Lower cost-to-power ratio  Ability to furl rotor out of wind  Active yaw drive  Access to power train assembly  Difficult maintenance
  16. 16. VAWT Advantages Disadvantages  No yaw mechanism  Ground-level blade installation (V-VAWT)  Good access to generator/gearbox  Lower wind speeds  Lower efficiency  Blade-wake interaction  Difficult to control overspeed  Problem starting
  17. 17. WIND MACHINE PERFORMANCE  No machine can extract 100 % of wind energy as the wind have to be brought to hault.  Most possible for a rotor is to decelerate wind by one third of its free velocity.  Only 60% of the available energy can be converted to mechanical energy by a 100% efficient aerogenerator.  More losses occur in gears, transmission systems and generators.  Hence, the turbine efficiency reduces to only about 35%.
  18. 18.  The overall conversion efficiency, of an aero generator of the general type is the ratio of useful output power to that of wind power input. o = Useful output power Wind input power = A. O. G. C. Gen A = efficiency of the aeroturbine G = efficiency of the gearing C = efficiency of the mechanical coupling Gen = efficiency of the generator where
  19. 19. Typical performance of wind machines
  20. 20.  The Savonious rotor and the American multiblade (farm windmill) are intended for low speed operation  The modern two blade type and Darrieus rotor type are intended for high speed operation more compatible with generating electric energy.  It may be concluded that a two blade propeller has potentially the best performance of the system considered.  This explains why virtually all large scale systems built in the past employed two or three bladed machines.
  21. 21. Performance of wind machines
  22. 22.  The multiblade types with high starting torque on the other hand are more suitable for pumping water.  In practice, it is impossible to build wind driven generators capable of operating at the same efficiency at all wind speeds.  There is wind speed below which no power can be generated because of friction losses.  As the wind speed increases, the extracted power is held constant by turning the blades on their axis to reduce effective area.  This decreases the power extracted and stabilizes the speed
  23. 23. Operation process  The extraction of power, and hence energy from the wind depends on creating certain forces and applying them to rotate (or to translate) a mechanism.  two primary mechanisms for producing forces from the wind; lift and drag.  By definition lift forces act perpendicular to the air flow, while drag forces act in the direction of flow.
  24. 24.  Lift forces are produced by changing the velocity of the air stream flowing over either side of the lifting surface  speeding up the air flow causes the pressure to drop, while slowing the air stream down leads to increase in pressure.  change in velocity generates a pressure difference across the lifting surface.  This pressure difference produces a force that begins to act on the high pressure side and moves towards the low pressure side of the lifting surface which is called an airfoil
  25. 25. Wind turbine components
  26. 26. Blade
  27. 27.  The cross-section of the blade has a streamlined asymmetrical shape  The blade profile is a hollow profile usually formed by two shell structures glued together  To make the blade sufficiently strong and stiff, so- called webs are glued onto the shells in the interior of the blade  this web will act like a beam
  28. 28.  It is important that the blade sections near the hub are able to resist forces and stresses from the rest of the blade.  So the blade profile near the root is both thick and wide.  Further, along the blade, the blade profile becomes thinner so as to obtain acceptable aerodynamic properties.  At the root, the blade profile is usually narrower and tubular to fit the hub.
  29. 29. Blade count The determination of the number of blades involves design considerations of •aerodynamic efficiency, •component costs, •system reliability, and •Aesthetics Aerodynamic efficiency increases with number of blades but with diminishing return. Increasing the number of blades from one to two yields a six percent increase in aerodynamic efficiency, whereas increasing the blade count from two to three yields only an additional three percent in efficiency. Further increasing the blade count yields minimal improvements in aerodynamic efficiency and sacrifices too much in blade stiffness as the blades become thinner.
  30. 30. Blade materials  Previously: wood and canvas were used  But use of these materials limits the shape of blade to a flat plate which has higher drag and thus reduces the aerodynamic efficiency  So nowadays composite materials such as fibre glass, aluminium, carbon fibres, FRP etc are used
  31. 31. Hub  The hub is the fixture for attaching the blades to the rotor shaft.  Consists of nodular cast iron.
  32. 32. Nacelle Main shaft  transmits the rotational energy from the rotor hub to the gearbox or directly to the generator. Main Bearing  Supports the main shaft and transmits the reactions from the rotor loads to the machine frame.  the spherical roller bearing type is often used
  33. 33. Main gear  act as a speed increaser and to transmit energy between the rotor and the generator.  Spur gear is most oftenly used. Mechanical brake  Mechanical brakes are usually used as a backup system for the aerodynamic braking system of the wind turbine. Generator  transforms mechanical energy into electric power.  Both synchronous and asynchronous generator can be used
  34. 34.  It is necessary that the turbine should be installed with certain minimum ground clearance and without any obstacle within the area with respect to the horizontal plane of the turbine.  In general, it is considered that a wind turbine should be at least 10m above any wind obstacle.  Above all, the tower must be strong enough to hold the system during extreme environmental condition. Types 1. Lattice tower 2. Guyed tower and 3. Solid tower
  35. 35. Battery Charge Controller  The main purpose of the charge controller is to check the battery and generator voltage and act accordingly.  After the battery voltage reaches the upper threshold voltage (which is predefined) it disconnects the wind turbine generator and connects to the ballast load.  The battery is normally connected to the primary load.  When the battery condition falls below the lower threshold voltage the primary load is now disconnected and the battery is connected to the wind turbine generator.
  36. 36. Tail  The wind turbine is always designed considering cut in and cut out wind speeds.  The turbine normally start turning at the wind speed of 3m/s.  The wind turbine must furl or turn out of the wind direction above the maximum wind speed (normally 16 m/sfor small wind turbine) .  So, in order to protect the turbine from breakage at higher wind speeds, a tail with the proper yaw angle (angle between wind direction and turbine axis) and furling is designed.  Normally, a tail is electrically driven for large wind turbine and free yaw for small turbines which helps in keeping the turbine facing towards the wind direction.
  37. 37. Wind Energy Resources Assessment in Nepal  Well established wind anemometers at 2 m and 3 m heights are available at 264 meteorological stations in Nepal.  Monitoring of the effect, due to wind, on the paddy growing in agricultural process.  These heights are not effective for wind power potential purpose.
  38. 38. Establishment of Wind Anemometers  Establishment of 5 anemometer stations by Water and Energy Commission Secretariat (WECS) in 2001;  Okhaldhunga (Site elevation: 1720m)  Nagarkot (Bhaktapur) (Site elevation : 2163m)  Butwal (Rupandehi), Palpa (Site elevation : 230m)  Kagbeni (Mustang) (Site elevation : 2820m)  Thini (Mustang) (Site elevation : 2645m)  Currently AEPC is monitoring these stations and collecting the data  Data already collected: Butwal (2000 to 2003); Nagarkot (2001 to 2004); Thini (2001 to 2004); Kagbeni (2001 to 2004); Palpa (2003 to 2004); Okhaldhunga (2002 to 2004)
  39. 39. Instrument Description  Each Station  contains two anemometers: at 10m and at 20m above ground.  automatically records wind data every hour by NRG 9300 data logger.  data record of up to 6 months can be stored in the NRG’s PCMCIA FLASH memory card (capacity 256 KB to 2 MB)  uploaded data can be analyzed by NRG 9300 Microsite system in computer.
  40. 40. Conclusion  Three blade HAWT is a best option in order to produce electricity and multi blade wind turbine can be used where there is a need of high starting torque like pump.  HAWT seems to be better wind turbine than VAWT.  Slight change in a wind velocity changes the extracted energy to a large extent.  Wind energy can be a contributing source of energy in the today’s scenario of load shedding in Nepal.  There is a lot of potential of wind energy in Nepal.
  41. 41. References   technology/chapter-6-small-wind-turbines/  Guidelines for Design of Wind Turbines, Det Norske Veritas, Copenhagen  Development of Technical Specifications and Standards for Small Scale Wind Energy, Kathmandu Alternative Power and Energy Group, Dhulikhel, Nepal 
  42. 42. THANK YOU