Design small scale wind turbine for home electricity generation

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Design small scale wind turbine for home electricity generation

  1. 1. Wind Turbine Design Project AE5 – Design Small Scale Wind Turbine for Home Electricity Generation March 2013 By Maheemal K.B. (0923688) Kalinga Ellawala (0628552) Bhavdeep Pancholi (0906043) Mishkath Harees (0806420) Abstract Wind Turbines are one the oldest known method used to extract energy from the natural sources (wind in this case). With the changing weather and wind speed, it is not possible to produce high constant power from the wind turbine but a small scale wind turbine can be used to power small appliances at home, e.g. fridge. This project looks into thetechnical and marketing aspects for an innovative design of a small scale wind turbine designed for supplying home electricity. The report includes content on design, enhancement, power management, manufacturing methods, cost analysis & marketing issues; processes which are considered for creating new patent and putting into development.
  2. 2. 1 | P a g e Acknowledgement (BP) We would like to express our gratitude to all those who gave us the possibility to complete this design project. We would like to thank Brunel School of Design & Engineering and all the professors involved in this module for giving us permission to commence this project in the first instance, to do the necessary research work and to use departmental data and knowledge. We also like to take this opportunity to thank our project supervisor Dr. A. Gatto whose help, suggestions and encouragement helped us stretch our ideas further then our own imaginations.
  3. 3. 2 | P a g e Table of Contents Abstract ................................................................................................................................................... 0 Acknowledgement (BP)........................................................................................................................... 1 1 Introduction (BP)............................................................................................................................. 0 1.1 Aim .......................................................................................................................................... 0 1.2 Design Brief ............................................................................................................................. 0 2 Current Designs (KE)........................................................................................................................ 1 2.1 Energy ball V200...................................................................................................................... 1 2.2 Honeywell WT6500 Wind Turbine .......................................................................................... 1 2.3 Hannevind 2.2 kW ................................................................................................................... 2 2.4 Windon 2 kW........................................................................................................................... 2 2.5 Bergey Excel............................................................................................................................. 3 2.6 Southwest Windpower Skystream 3.7.................................................................................... 3 2.7 Windsave WS500..................................................................................................................... 3 2.8 Renewable Devices – Swift...................................................................................................... 4 3 The Wind (BP).................................................................................................................................. 4 3.1 Geographical Analysis.............................................................................................................. 4 3.2 UK Historical Data.................................................................................................................... 6 4 The Wind & the Blades.................................................................................................................... 7 4.1 Wind power calculations......................................................................................................... 7 4.2 The Blades ............................................................................................................................... 9 4.2.1 Number of Blades............................................................................................................ 9 4.2.2 Aerofoil & Load................................................................................................................ 9 4.2.3 Materials........................................................................................................................ 12 4.2.4 Wind Speed ................................................................................................................... 12 4.2.5 Angle of Attack .............................................................................................................. 13 4.3 Power Extracted.................................................................................................................... 13 4.4 Acoustics & Insulation........................................................................................................... 13 5 Generator (KE)............................................................................................................................... 14 5.1 AC & DC Generator................................................................................................................ 14 5.2 Induction Generator.............................................................................................................. 15 5.3 Generator types .................................................................................................................... 15 5.3.1 Synchronous Generator (SG)......................................................................................... 15 5.3.2 Permanent magnet synchronous Generator (PMSG) ................................................... 15 5.3.3 Switched reluctance generator (SRG) ........................................................................... 16 5.4 Permanent magnet generators............................................................................................. 16 5.4.1 The magnetic flux orientation (Radial Flux or Axial Flux).............................................. 17 5.4.2 Longitudinal or Transversal (Figure 5.4.1)..................................................................... 17
  4. 4. 3 | P a g e 5.4.3 Inner Rotor or Outer Rotor............................................................................................ 18 5.5 Coil winding arrangements ................................................................................................... 18 5.5.1 Coil placement............................................................................................................... 18 5.5.2 Coil winding distribution ............................................................................................... 19 5.5.3 Pole slot combinations .................................................................................................. 19 6 Advantages and Disadvantages of Wind Turbine Designs (MT).................................................... 19 6.1 Horizontal Axis Wind Turbines.............................................................................................. 19 6.1.1 Advantages of Horizontal Axis Wind Turbines .............................................................. 19 6.1.2 Disadvantages of Horizontal Axis Wind Turbines.......................................................... 20 6.2 Vertical Axis Wind Turbines................................................................................................... 20 6.2.1 Advantages of Vertical Axis Wind Turbines................................................................... 21 6.2.2 Environmental Benefits................................................................................................. 21 6.3 Comparison between Vertical designs Vs. Horizontal designs ............................................. 21 6.4 Justification for design choice............................................................................................... 22 7 Wind Turbine Power Management (MH)...................................................................................... 22 8 Safety Systems for Wind Turbines (MH) ....................................................................................... 23 8.1 Vibration Sensors .................................................................................................................. 23 8.2 Turbine over-speed ............................................................................................................... 24 8.3 Thermal and other sensors.................................................................................................... 24 8.4 Anti-Icing Systems ................................................................................................................. 24 8.5 Material Failure ..................................................................................................................... 24 9 Manufacturing Methodology and Processes (MH) ....................................................................... 25 9.1 Design for Manufacture/Design for Assembly...................................................................... 25 9.2 Material Selection ................................................................................................................. 26 9.3 Material Properties ............................................................................................................... 26 9.4 Cost and Availability.............................................................................................................. 27 9.5 Selection of manufacturing processes .................................................................................. 27 9.6 Metal and Metal Alloys ......................................................................................................... 28 9.7 Metal Casting Processes........................................................................................................ 28 9.8 Sand Casting .......................................................................................................................... 30 9.9 Sands ..................................................................................................................................... 31 9.10 Types of Sand Moulds ........................................................................................................... 31 9.11 Patterns ................................................................................................................................. 31 9.12 Sand-Moulding Machines...................................................................................................... 32 9.13 The Sand Casting Operation.................................................................................................. 32 9.14 Die Casting............................................................................................................................. 33 9.15 Hot-Chamber Process............................................................................................................ 33 9.16 Cold-Chamber Process .......................................................................................................... 33
  5. 5. 4 | P a g e 9.17 Process Capabilities and Machine Selection ......................................................................... 34 9.18 Forging of Metals................................................................................................................... 34 9.19 Extrusion and Drawing of Metals.......................................................................................... 35 9.20 Forming and Shaping Plastics................................................................................................ 35 9.21 Injection Moulding ................................................................................................................ 36 9.22 Process Capabilities............................................................................................................... 37 9.23 Rotational Moulding.............................................................................................................. 37 10 Product Design Specification (MH/MT)..................................................................................... 38 11 Design Conceptualisation.......................................................................................................... 41 11.1 Blade (BP) .............................................................................................................................. 41 11.1.1 Design 1......................................................................................................................... 42 11.1.2 Design 2......................................................................................................................... 42 11.1.3 Design 3......................................................................................................................... 42 11.1.4 Aerofoil Shape ............................................................................................................... 43 11.1.5 Materials........................................................................................................................ 43 11.2 Generator (KE)....................................................................................................................... 43 11.2.1 Design 1......................................................................................................................... 43 11.2.2 Design 2......................................................................................................................... 44 11.2.3 Design 3......................................................................................................................... 45 11.2.4 Design 4......................................................................................................................... 45 11.3 Preliminary Design of braking and mounting systems (MH)................................................. 46 11.3.1 Braking Systems............................................................................................................. 46 11.3.2 Braking System Design 1 ............................................................................................... 46 11.3.3 Braking System Design 2 ............................................................................................... 46 11.3.4 Braking System Design 3 ............................................................................................... 47 11.4 Mounting System (MH)......................................................................................................... 47 11.4.1 Mounting System Method 1.......................................................................................... 47 11.4.2 Mounting system 2........................................................................................................ 48 11.4.3 Mounting System 3 ....................................................................................................... 48 11.5 Popular Wind turbine arrangements for domestic use (MT)................................................ 49 11.5.1 Introduction................................................................................................................... 49 11.5.2 Series Regulators........................................................................................................... 49 11.5.3 Shunt Regulators ........................................................................................................... 50 11.5.4 Two modes of operation............................................................................................... 50 11.5.5 Pulse Width Modulation Regulators ............................................................................. 50 11.5.6 PWM regulator with a dump load................................................................................. 51 11.5.7 Shorting the generator output? .................................................................................... 51 11.5.8 Wind compatible “Solar style” charge controllers? ...................................................... 51
  6. 6. 5 | P a g e 11.5.9 Maximum Power Point Tracking ................................................................................... 52 11.5.10 Hysteresis .................................................................................................................. 52 11.5.11 Lead-Acid Batteries.................................................................................................... 52 11.5.12 Dump Loads (as used in 'battery shunt' configuration) ............................................ 53 11.5.13 Braking Resistor (as used in 'turbine brake controller' configuration) ..................... 53 11.5.14 Grid Tie Inverters....................................................................................................... 53 12 Preliminary Design & Analysis................................................................................................... 54 12.1 The Blades, the Hub & the Cone (BP).................................................................................... 54 12.2 Generator design selection (KE)............................................................................................ 55 12.2.1 Design Selection ............................................................................................................ 55 12.2.2 Design improvements for the preliminary generator design........................................ 56 13 Final Design (BP)........................................................................................................................ 57 13.1 FEA Analysis (MT) .................................................................................................................. 59 13.2 Bill of Material (MT) .............................................................................................................. 62 13.3 Blades (BP)............................................................................................................................. 63 13.4 Bearings (BP/MH).................................................................................................................. 64 13.5 Final Generator Design (KE) .................................................................................................. 64 13.5.1 Rotor.............................................................................................................................. 64 13.5.2 Stator............................................................................................................................. 65 13.5.3 Final assembly of the generator.................................................................................... 66 13.5.4 Power Calculations........................................................................................................ 67 13.5.5 Power Curve .................................................................................................................. 69 13.5.6 Method.......................................................................................................................... 69 13.5.7 Generator circuit (stator to blade point)....................................................................... 70 13.6 Power Management (MT)..................................................................................................... 70 13.7 Maintenance (ALL) ................................................................................................................ 71 13.7.1 Generator ...................................................................................................................... 71 13.7.2 Tips for long lasting power management system ......................................................... 72 14 Manufacturing (MH).................................................................................................................. 72 15 Business Model Evaluation of wind turbine (MH)..................................................................... 73 15.1 Material Costs........................................................................................................................ 73 15.2 Manufacturing Costs ............................................................................................................. 75 15.3 Marketing Costs..................................................................................................................... 75 15.4 Premises Costs....................................................................................................................... 76 15.5 Labour/staffing Costs ............................................................................................................ 76 15.6 Operational Costs.................................................................................................................. 77 15.7 Revenue................................................................................................................................. 78 15.8 Profit Margins........................................................................................................................ 78
  7. 7. 6 | P a g e 16 Conclusion (KE/MT)................................................................................................................... 84 16.1 Design Specification .............................................................................................................. 84 17 Works Cited............................................................................................................................... 85 18 Appendix-A (ALL)....................................................................................................................... 87 18.1 Figures ................................................................................................................................... 87 18.2 Flow chart for varying conditions (MT)................................................................................. 90 19 Appendix-B (MT)........................................................................................................................ 91 20 Appendix-C (ALL) ....................................................................................................................... 92
  8. 8. 1 Introduction (BP) With increasing awareness of global warming due to Carbon Dioxide produced from the burning fuels, the use of natural energy source is coming into effect. Engineers are adapting the use of natural sources (e.g. wind, solar, hydro) to generate electricity and provide power to the power plants. The use of wind turbine is one of the oldest known methods of extracting the energy from natural sources. Windmills were used in olden times to run the pump for pumping the water from the well. Wind turbines are not well considered because they heavily depend on the wind blowing along with the geographical disturbance however, a small scale wind turbine can be used to power small home appliances reducing the cost of electricity and fuel burnt to produce equal amount of electricity. Wind turbine extracts energy from the wind to generate electricity. 40% of all the wind energy in Europe blows over the UK, making it an ideal country for domestic turbines (known as 'microwind' or 'small-wind' turbines). A typical system in an exposed site could easily generate more power than household lamps and other electrical appliances use. Just like any engineering design poses challenges, household wind turbine also poses various challenges such as noise, aesthetics, buying cost, maintenance cost, etc. This report looks into the current designs of the small scale wind turbine along with the market requirement followed by the design of an innovative wind turbine system. In the report areas such as current designs, power generation, blade design power management and fail safe methods are considered. The report also considers the development complications limiting the design enhancement such as noise, aesthetics, material cost, maintenance, legal constraints and other issues. These are the issue which affect the design, manufacturing and marketing of the product. 1.1 Aim The main aim of the project is to design a small wind turbine that can generate electricity for home appliances. The thought of design directs us to look into the various aspects such as manufacturing, noise, cost which leads us to our additional aim of analysing the system to overcome the usual technical glitches. 1.2 Design Brief The project brief involves the design of a small scale wind turbine that can be easily mass produced and fitted to every household in the UK to aid electricity consumption. The design should provide the following; 1. Be able to generate a non-trivial electricity supply to the household when operating. Excess electricity can be fed back into the national grid or charge secondary batteries. 2. The scale of the turbine should be within the limits of the UK building code and not dominate the aesthetics of the average dwelling. 3. Designed to operate at suitable wind speeds typical to UK weather in urban environments. 4. Possess a fail-safe system as a consequence of an over-speed event. 5. Have a low acoustic footprint. The above brief for this project can be simplified further to manage the project. Simplified brief below shows that this project provides us with an opportunity to look into various sections which will help us complete the task. The several tasks to be completed for this project are as follows: • Evaluation of the working environment for the turbine in the UK – wind speeds, weather, etc. • Calculation of the aerodynamic design and structural loads
  9. 9. • Selection of the materials & equipme • Investigation of mass production methods • Cost/Benefit analysis of the system • Considerations for safety system during extreme events • Noise reduction methods and its implementation into design 2 Current Designs (KE) 2.1 Energy ball V200 Energy ball V200 (SeeFigure 1) is a unique turbine design when compared to the traditional three blade wind turbines. The design consists of six rotor blades that are asse The turbine weights 90kg, turbine diameter of 1.98m and minimum start up wind speed of 3 m/s. Due to the unique design and the venture effect, the generator harness wind more efficiently. The electricity generated from V200 the electric socket (Plug-in product) of the property. The Inverter is connected to the property electric breaker box. The energy harvest from V200 can be used to charge batteries and excess unused energy automatically dumped in to the grid. The Energy ball categorised as a noise less, since the turbine does not have any wing tips it does not generate the ‘’swishing’’ noise. The Energy ball’s dimensions allow it to be installed in many countrie vibration (noise less) and less shadows it ideally suited for residential or commercial rood top usage. Figure 90 shows the power curve of the Energy ball V200 which shows the turbines operating parameters (1). 2.2 Honeywell WT6500 Wind Turbine Selection of the materials & equipment – battery, metal, coils, etc. Investigation of mass production methods Cost/Benefit analysis of the system – power generated and its cost effective use y system during extreme events reduction methods and its implementation into design (KE) Figure 1: Energy Ball V200 ) is a unique turbine design when compared to the traditional three blade wind turbines. The design consists of six rotor blades that are assembled as a sphere shape. The turbine weights 90kg, turbine diameter of 1.98m and minimum start up wind speed of 3 m/s. Due to the unique design and the venture effect, the generator harness wind more efficiently. The electricity generated from V200 Energy ball comes to direct use where it can be plugged in straight to in product) of the property. The Inverter is connected to the property electric breaker box. The energy harvest from V200 can be used to charge batteries and excess nused energy automatically dumped in to the grid. The Energy ball categorised as a noise less, since the turbine does not have any wing tips it does not generate the ‘’swishing’’ noise. The Energy ball’s dimensions allow it to be installed in many countries urban areas. Also it features such as less vibration (noise less) and less shadows it ideally suited for residential or commercial rood top usage. shows the power curve of the Energy ball V200 which shows the turbines operating WT6500 Wind Turbine Figure 2: Honeywell WT6500 1 | P a g e ted and its cost effective use ) is a unique turbine design when compared to the traditional three mbled as a sphere shape. The turbine weights 90kg, turbine diameter of 1.98m and minimum start up wind speed of 3 m/s. Due to the unique design and the venture effect, the generator harness wind more efficiently. The ball comes to direct use where it can be plugged in straight to in product) of the property. The Inverter is connected to the property electric breaker box. The energy harvest from V200 can be used to charge batteries and excess nused energy automatically dumped in to the grid. The Energy ball categorised as a noise less, since the turbine does not have any wing tips it does not generate the ‘’swishing’’ noise. The Energy ball’s s urban areas. Also it features such as less vibration (noise less) and less shadows it ideally suited for residential or commercial rood top usage. shows the power curve of the Energy ball V200 which shows the turbines operating
  10. 10. The Honeywell Wind Turbine (see weight of 110 kg and generates on average up to 1500 kWh per year depending on height and location. The Honeywell Wind Turbine’s blad and the unique multi - stage blade design enables the system to react quickly and efficiently to change in wind a speed which ensures that the maximum wind energy is captured without the typical noise and vibration associated with traditional wind turbines. The Wind Turbine has an increased operating span over traditional turbines with a start auto shut off at 38 mph (17.0 m/s). 2.3 Hannevind 2.2 kW The Hannevind wind turbine (see glass fiber. Since the diameter of the turbine is 3.5 meters it required to a The tower can be high between 12 to 18 meters and it weight around 100 kg. The turbine operates at minimum wind speed of 2.4 m/s and the maximum power is generates at the wind speed of 9 m/s. At the rear end of the turbine there i wind for capture as much wind energy as possible. The turbine can be connected to the electric grid, work solo or be connected with some other kind of electric device 2.4 Windon 2 kW The Windon 2kW (SeeFigure 4) is a turbine which has three blades with a diameter of 3.2 meters. Back on the turbine is a fin, which helps the turbine to steer up against the wind so that maximum effect can be received. The tower can be 9 or 12 meters high, and the weight of the turbine is approximately 40 kg. The minimum wind for the turbine to start generate electricity is 2.5 m/s. The wind turbine is very quiet and demands very little service and maintenance. turbine power curve (4). The Honeywell Wind Turbine (seeFigure 2) is a gearless wind turbine, which the diameter of 1.8 m, weight of 110 kg and generates on average up to 1500 kWh per year depending on height and location. The Honeywell Wind Turbine’s blade tip power system (BTPS) is a perimeter power system stage blade design enables the system to react quickly and efficiently to change in wind a speed which ensures that the maximum wind energy is captured without the typical nd vibration associated with traditional wind turbines. The Wind Turbine has an increased operating span over traditional turbines with a start-up speed as low as 0.5 mph (0.2 m/s), with an auto shut off at 38 mph (17.0 m/s). Figure 91shows the power curve for WT600 (2) Hannevind 2.2 kW Figure 3: Hannevind Wind Turbine (seeFigure 3) equipped with typical classic look of three blades made of glass fiber. Since the diameter of the turbine is 3.5 meters it required to acquire a building permit. The tower can be high between 12 to 18 meters and it weight around 100 kg. The turbine operates at minimum wind speed of 2.4 m/s and the maximum power is generates at the wind speed of 9 m/s. At the rear end of the turbine there is a fin mounted which helps it to steer the turbine up towards the wind for capture as much wind energy as possible. The turbine can be connected to the electric grid, work solo or be connected with some other kind of electric device (3). ) is a turbine which has three blades with a diameter of 3.2 meters. Back on the turbine is a fin, which helps the turbine to steer up against the wind so that maximum The tower can be 9 or 12 meters high, and the weight of the turbine is approximately 40 kg. The minimum wind for the turbine to start generate electricity is 2.5 m/s. The wind turbine is very quiet and demands very little service and maintenance. Figure 4: Windon Wind Turbine 2 | P a g e ) is a gearless wind turbine, which the diameter of 1.8 m, weight of 110 kg and generates on average up to 1500 kWh per year depending on height and e tip power system (BTPS) is a perimeter power system stage blade design enables the system to react quickly and efficiently to change in wind a speed which ensures that the maximum wind energy is captured without the typical nd vibration associated with traditional wind turbines. The Wind Turbine has an increased up speed as low as 0.5 mph (0.2 m/s), with an (2). ) equipped with typical classic look of three blades made of cquire a building permit. The tower can be high between 12 to 18 meters and it weight around 100 kg. The turbine operates at minimum wind speed of 2.4 m/s and the maximum power is generates at the wind speed of 9 m/s. At s a fin mounted which helps it to steer the turbine up towards the wind for capture as much wind energy as possible. The turbine can be connected to the electric grid, ) is a turbine which has three blades with a diameter of 3.2 meters. Back on the turbine is a fin, which helps the turbine to steer up against the wind so that maximum The tower can be 9 or 12 meters high, and the weight of the turbine is approximately 40 kg. The minimum wind for the turbine to start generate electricity is 2.5 m/s. The wind turbine is very quiet and demands very little service and maintenance. Figure 92 shows the
  11. 11. 2.5 Bergey Excel The Bergey Excel (See Figure 5 operation in adverse weather conditions. When connec the electricity for an average total electric home at moderate wind sites. Start-up Wind speed at 7.5 mph and battery charging. The Estimated Energy Production of 12.5mph (5). 2.6 Southwest Windpower Skystream 3.7 The Skystream 3.7(See Figure 6) is designed for residential use which is the first fully integrated and grid-tied wind energy system designed for that purposes. inclusive wind generator with controls and inverter built in designed to provide quiet, clean electricity in very low wind speeds. The Skystream 3.7 operates to downwind because it has no tail rudder to keep it facing into the w outputs and peak capacity of 2.6 kW. The Start The interconnection can be either and a brushless permanent magnet. The turbine generates total estimated energy production of 2.7 Windsave WS500 The Windsave WS500 (See Figure Windsave WS 1000 is 1.75 m in diameter and rated at 1000 W at 12 m/s. Both these ratings imply a Figure 5: Bergey Excel 5) is designed for high reliability, low maintenance and automatic operation in adverse weather conditions. When connected to the grid the turbine provide most of the electricity for an average total electric home at moderate wind sites. Rated Capacity of 7.5 mph and rotor size of 6.7 m, Interconnection can be Estimated Energy Production of 1500 KWh per month at a wind speed of Southwest Windpower Skystream 3.7 ) is designed for residential use which is the first fully integrated and tied wind energy system designed for that purposes. This ‘plug and play inclusive wind generator with controls and inverter built in designed to provide quiet, clean electricity in very low wind speeds. The Skystream 3.7 operates to downwind because it has no tail rudder to keep it facing into the wind. The turbine has a Rated Capacity of outputs and peak capacity of 2.6 kW. The Start-up wind speed of 8mph and the r can be either utility connected or battery charging. It has a gear less brushless permanent magnet. The turbine generates total voltage output of estimated energy production of 400 kWh per month at wind speed of 5.4 m/s (6) Figure 6: Skystream 3.7 Figure 7) is 1.25 m in diameter and rated at 500 W at 12 m/s and the Windsave WS 1000 is 1.75 m in diameter and rated at 1000 W at 12 m/s. Both these ratings imply a 3 | P a g e ) is designed for high reliability, low maintenance and automatic ted to the grid the turbine provide most of Rated Capacity of 10kw, Interconnection can be Utility connected or 1500 KWh per month at a wind speed of ) is designed for residential use which is the first fully integrated and and play’ turbine is an all- inclusive wind generator with controls and inverter built in designed to provide quiet, clean electricity in very low wind speeds. The Skystream 3.7 operates to downwind because it has no tail Rated Capacity of 1.9 kW continuous 8mph and the rotor size of 3.72m. utility connected or battery charging. It has a gear less alternator voltage output of 240 VAC and (6). ) is 1.25 m in diameter and rated at 500 W at 12 m/s and the Windsave WS 1000 is 1.75 m in diameter and rated at 1000 W at 12 m/s. Both these ratings imply a
  12. 12. coefficient of performance (power which would be an extremely good performance for a micro wind turbine, which, at that size, might have been more expected to have maximum coefficient of performance between 0.11 and 0.19 2.8 Renewable Devices The Swift turbine (SeeFigure 8) has a blade diameter of 1.8 meters and start in wind speed at 4 m/s. The turbine rated output power of 2200W and output voltage of 120V. The design en Renewable Devices claim that it is the world’s first truly silent wind turbine. The Swift has some very advanced aerodynamics that make the rotor more efficient, whilst reducing the noise emissions significantly, a problem which has meant that s circular rim around the outside of the blades restricts the radial flow of air at the tip of each blade that creates a ripping noise with conventional turbines. Renewable Devices has also developed an electronic control system that safeguards the turbine in high winds and ensures efficient power extraction under normal operating conditions 3 The Wind (BP) 3.1 Geographical Analysis Wind turbine generates electricity by extracting energy from the wind. Earth’s circulation system, driven by its magnetic poles and the temperature gradient (across its latitude), sets the wind direction and its speed. It gets affected by the landscape, the geometry and the speed it’s flowing across or around. Flowing with unique characteristics, the wind carries energy of th be used to generate lift or drag force show how the wind gets affected by the general landscape aided by the data of UK Mean Wind Speed. coefficient of performance (power produced by turbine divided by power in the wind) of about 0.38, which would be an extremely good performance for a micro wind turbine, which, at that size, might have been more expected to have maximum coefficient of performance between 0.11 and 0.19 Figure 7: Windsave Renewable Devices – Swift ) has a blade diameter of 1.8 meters and start in wind speed at 4 m/s. The turbine rated output power of 2200W and output voltage of 120V. The design en Renewable Devices claim that it is the world’s first truly silent wind turbine. The Swift has some very advanced aerodynamics that make the rotor more efficient, whilst reducing the noise emissions significantly, a problem which has meant that similar sized turbines cannot be building mounted. A circular rim around the outside of the blades restricts the radial flow of air at the tip of each blade that creates a ripping noise with conventional turbines. Renewable Devices has also developed an ctronic control system that safeguards the turbine in high winds and ensures efficient power extraction under normal operating conditions (8). Figure 8: Swift Geographical Analysis Wind turbine generates electricity by extracting energy from the wind. Earth’s circulation system, poles and the temperature gradient (across its latitude), sets the wind direction and its speed. It gets affected by the landscape, the geometry and the speed it’s flowing across or around. Flowing with unique characteristics, the wind carries energy of th force as a result of a pressure difference. The following paragraph will show how the wind gets affected by the general landscape aided by the data of UK Mean Wind 4 | P a g e produced by turbine divided by power in the wind) of about 0.38, which would be an extremely good performance for a micro wind turbine, which, at that size, might have been more expected to have maximum coefficient of performance between 0.11 and 0.19 (7). ) has a blade diameter of 1.8 meters and start in wind speed at 4 m/s. The turbine rated output power of 2200W and output voltage of 120V. The design engineers of Renewable Devices claim that it is the world’s first truly silent wind turbine. The Swift has some very advanced aerodynamics that make the rotor more efficient, whilst reducing the noise emissions imilar sized turbines cannot be building mounted. A circular rim around the outside of the blades restricts the radial flow of air at the tip of each blade that creates a ripping noise with conventional turbines. Renewable Devices has also developed an ctronic control system that safeguards the turbine in high winds and ensures efficient power Wind turbine generates electricity by extracting energy from the wind. Earth’s circulation system, poles and the temperature gradient (across its latitude), sets the wind direction and its speed. It gets affected by the landscape, the geometry and the speed it’s flowing across or around. Flowing with unique characteristics, the wind carries energy of the form which can as a result of a pressure difference. The following paragraph will show how the wind gets affected by the general landscape aided by the data of UK Mean Wind
  13. 13. 5 | P a g e Figure 9: Microscale modelling around Wellington (9) Wind flowing over various landscapes can get affected by its geometrical appearance. Figure 9shows a classic example of how the wind gets affected by the landscape. It shows graphical presentation of the CFD simulation carried for a micro scale model over the Wellington area.The wind cannot be seen in real life but can be visualised as stream of particles flowing in a line (either straight or random chaotic line). Figure 10&Figure 11shows animated behaviour of the wind flow over the mountain and the cliff. Figure 10: Wind Flow near the Cliff (10) Figure 11: Wind Flow over the Hill (10) The purpose of this analysis is to show that the undisturbed flow of air is mostly uniform.However when it flows around or across a geometry or a landscape, it creates turbulence. This turbulent air/wind includes random movement of the air particles which leads to loss of energy the wind contains. Therefore wind turbine needs to be placed on a landscape that places rotor and blades in average wind flow but with little of turbulence created by the surroundings. Artificial or natural surroundings can potentially create turbulence. Artificial surroundings include the houses and buildings. Figure 12&Figure 13 shows CFD Analysis carried out by S J Watson at Loughborough University. Figure 12displays filled vector plot of a house in isolated area and how wind (flowing from left to right) creates wake resulting in no or low velocity with a change in direction. Figure 13displays a filled vector plot of a house in urban area which shows wind flow (left to right). In urban area there is only small amount of wind flowing below the roof tops and because of this, minimum turbulence is created before and aft of house.
  14. 14. 6 | P a g e Figure 12: CFD Analysis of Wind Flow - Isolated Area (11) Figure 13: CFD Analysis of Wind Flow - Urban area (11) The wind analysis of different landscape and geometrical obstacles suggest that the wind turbine needs to be placed in open area where landscape does not create wake. If the turbine is to be placed on top of a house roof, it needs to be place on the upwind side of the roof as downwind side has high turbulence close to the roof. If the wind turbine is to be placed near the cliff top or on mountain, it needs to be high above the ground as the turbulence is high near to the terrain. However at very high level from ground, wind speed is not high therefore a balance must be found by collecting data over certain period of time at different height scales. 3.2 UK Historical Data Weather changes with time bringing in new seasons with different climate conditions. The Met office provides us with some average data on Mean Wind Speed measured at various regions in UK. This data will help us identify the wind speed limit we are expected to incorporate while designing small scale wind turbine for home electricity. e Figure 14: Mean Wind Speed 1971-2000 Spring (12) Figure 15: Mean Wind Speed 1971-2000 Summer (12)
  15. 15. 7 | P a g e Figure 16: Mean Wind Speed 1971-2000 Autumn (12) Figure 17: Mean Wind Speed 1971-2000 Winter (12) The data above clearly shows that the mean wind speed varies between 6-25 m/s at various regions in UK. Climate conditions also play important role in wind speeds as seen from the figures above. In summer, the wind speed measured in most urban areas is below 10 m/s and towards the Scotland side it picks up to 25 m/s. however in winter, the urban areas experience wind speed of 10-15 m/s and areas in Scotland and North Wales experience wind speed greater than 25 m/s. some part in changing wind speed. Therefore if the small wind turbine is to be designed for UK households, then it should be able to work at speeds low as 3-6 m/s and should also be able to sustain high wind speeds of around 25 m/s. 4 The Wind &the Blades 4.1 Wind power calculations Kinetic Energy of a mass in motion is given by ‫ܧ‬ = 1 2 ݉‫ݒ‬ଶ Equation 1: Kinetic Energy But the power is the rate of change of energy: ܲ = ݀‫ܧ‬ ݀‫ݐ‬ Equation 2: Power If the kinetic energy of the wind is considered to have constant velocity then the power of the wind can be calculated by ܲ = ଵ ଶ ‫ݒ‬ଶ ௗ௠ ௗ௧ , where ௗ௠ ௗ௧ = ߩ‫ܣ‬ ௗ௫ ௗ௧ Therefore, ܲ = 1 2 ߩ‫ݒܣ‬ଷ Equation 3: Wind Power (13) Whereρ is the Density, A is the Sweap Area and v is the Velocity of the wind.
  16. 16. 8 | P a g e Figure 18: Wind Turbine Sweap Area (13) The above calculation only helps us to find out the wind power with specific wind velocity. The wind turbine however does not extract all the power from the wind. Some of the energy is used to overcome the profile drag (14) created by the blade geometry and the leftover energy is allowed to pass through as extracting all the energy from the wind would mean accumulation of static pressure particles aft of wind turbine blades. Imagine an ‘Axial Stream Tube’ around a wind turbine as shown in Figure 19; if the energy is extracted between stage 2 and 3, the pressure accumulation would divert the incoming flow around the blade rather than passing through the blades. By extracting the power, the turbine reduces the wind kinetic energy. Therefore the air moves more slowly downstream of turbine compare to the upstream. This accumulates wind behind the turbine sweap area (downstream) as its moving slowly after the energy extraction. As a result the approaching (upstream) wind diverts around the turbine blades to avoid slow moving air. For these very reason ‘there is an optimum amount of power to extract from a given disc diameter’ (15). ‘The ideal is to reduce the wind speed by about two thirds downwind of the turbine, though even then the wind just before the turbine will have lost about a third of its speed. This allows a theoretical maximum of 59% of the wind’s power to be captured (this is called Betz’s limit)’ (15). Figure 19: Axial Stream Tube around a Wind Turbine (16) So by taking the Betz’s limit in consideration, the power available from the wind is given by the formula below where η is the Betz’s limit (generally given by ଵ଺ ଶ଻ ratio). ܲ = 1 2 ߟߩ‫ݒܣ‬ଷ Equation 4: Power Available Even after applying the Betz’s limit, the wind contains energy enough to drive the blades &generator and produce electricity. However, it depends on the blade design and its efficiency across the span to determine how much energy is extracted. While talking efficiency, we are faced by various design &mechanical limitations, therefore design of the blades will be considered even further in the next section as the blades play keep role in extracting the energy from the wind.
  17. 17. 9 | P a g e 4.2 The Blades Starting from design needs, considering manufacturing & materials’ limit and finishing with the power efficiency, the wind turbine blades are shaped to generate the maximum power from the wind The design engineers have to consider the following while designing the turbine blade: • Number of Blades • Aerofoil & Load • Materials • Rotational Speed • Wind speed • Pitch Control 4.2.1 Number of Blades Betz’s limit places significant restriction on the power that can be extracted by the blades. The limitation means more blades there are, the less power each can extract. However this allows us to reduce the blade length (span) and chord. ‘The other factor influencing the number of blades is aesthetics: it is generally accepted that three-bladed turbines are less visually disturbing than one or two-bladed designs’ (15). Also the number of blades adds to the weight which creates moment about the centre (mast or pillar). This moment is counter acted by the moment generated by the weight of the tail fin. Therefore increasing the number of blades would also require increasing the weight of the tail fin by changing the geometry or the distance its acting at from the centre or by using a denser material for the tail fin. Blades generate lift and this lift providesacceleration for the angular rotation. Hence the reason blades need to be manufactured precisely and increasing the number of blades would increase the cost of manufacturing. 4.2.2 Aerofoil & Load The turbine blades extract energy from the wind by using wind energy to generate the lift force. It uses same concept as the aeroplane wing in order to generate the lift force. ‫ܮ‬ = 1 2 ‫ܥ‬௅ߩ‫ݒ‬ଶ ܵ Equation 5: Finite Wing Lift Equation The equation above shows the finite wing lift equation which uses the finite wing CL value to work out the lift. If we look at the cross section of the wind turbine blade at particular point, we would see an airfoil shape. Air flowing over an airfoil shape generates lift due to the pressure difference. The best lift/drag characteristics are obtained by an airfoil that has thickness approximately 10-15% of its chord length (15). The lift can be increased by increasing the angle of attack but it also increases drag and potential of flow separation (Figure 21). For a particular airfoil shape coefficient of lift to angle of attack graph (Figure 22) is used to best describe the relation between lift and the angle of attack. Figure 20: Lift and Drag Vectors (15)
  18. 18. 10 | P a g e Figure 21: Aerofoil Shape & the Angle of Attack (15) Figure 22: Typical CL Graph (14) The figure above shows the graph for Infinite and Finite Wing Coefficient of lift where infinite wing curve is mostly based on experimental and computation analysis and finite wing lift can be worked using the following formula: ‫ܥ‬௅ഀ = ‫ܥ‬௟ഀ 1 + ହ଻.ଷ ஼೗ഀ గ௘஺ோ Equation 6: Finite Wing CL Gradient (14) Where CLα is the finite wing coefficient of lift curve gradient worked using infinite wing coefficient of lift curve gradient (Clα), aspect ratio (AR) and the span efficiency factor (e). Using this equation the coefficient of the lift and the lift itself can be worked out for a blade design however, the drag affects needs to be considered. The drag force on wind turbine blade is used to rotate the blades for VAWT but for HAWT it adds to the loss of energy from the wind and also adds to the structural load applied to the blade and the whole system. Drag force acting on the blade is given by the following equation: ‫ܦ‬ = 1 2 ‫ܥ‬஽ߩ‫ݒ‬ଶ ܵ Equation 7: Finite Wing Drag Force Where CD is: ‫ܥ‬஽ = ‫ܥ‬ௗ + ‫ܥ‬௅ ଶ ߨ݁‫ܴܣ‬ Equation 8: Finite Wing Drag Coefficient(14) The above equation uses finite wing coefficient of lift value along with the aspect ration, span efficiency factor and airfoil profile drag (skin friction drag + pressure drag) to calculate the Finite
  19. 19. 11 | P a g e Wing Drag. With the method of calculating the lift and drag for wind turbine blade, the design of the blade can be altered to maximize its efficiency. To improve the blade efficiency, the blade thick needs to be reduced relative to its width and this has effect on the aerofoil shape and the loading of the material. Also the apparent wind, wind blowing at an angle (Figure 23), ‘rotates the angles of the lift and drag to reduce the effect of lift force pulling the blade round and increase the effect of drag slowing it down. It also means that the lift force contributes to the thrust on the rotor’ (15). Hence the reason the blade needs to be turned further at the tips than at the roots, approximately around 10-20°. Figure 23: Apparent Wind Angle (15) As mentioned earlier, the best lift/drag characteristics are obtained by an aerofoil that has thickness approximately 10-15% of its chord length. However the due to structural requirements, the blade needs to support the lift, drag and gravitational forces acting on it, the aerofoil needs to be thicker than the aerodynamic optimum. The blade needs to be even thicker towards the root (where the blade attaches to the hub) where the bending forces are greatest. Because the apparent wind is moving slowly near to the roots (Figure 24), the need of aerodynamic efficiency is low. In which case some designers use a “flatback” section (Figure 25) closer to the roots as it gives high structural strength at the root attachment area but the attention needs to made as the section cannot get too thick for its chord length or the air flow will separate. Figure 24: Apparent Wind across the Blade(15)
  20. 20. 12 | P a g e Figure 25: Flatback Section (15) 4.2.3 Materials To maintain optimum solidity and high aerodynamic efficiency, thickness of the blade is compromised. This makes it difficult to build the strong blades as thin material can flutter and fracture eventually. To build a strong blade, material such as Pre-Preg carbon can be used which is stiffer and stronger then glass fibre but drives the cost of material high. For a small scale wind turbine blade material; aluminium alloy, iron, wood or strong plastic are more suitable due to its low cost of manufacturing compared to carbon fibre (blade aerofoil shape does affect the manufacturing cost). 4.2.4 Wind Speed The wind speed is also taken into consideration when design the turbine blade. The wind speed sets the Reynolds Number given by: ܴ݁ = ߩ‫ܿݑ‬ ߤ Equation 9: Reynolds Number for flow around Turbine Blade where u is the wind speed velocity, c is the blade chord length and µ is the dynamic viscosity of the fluid (air in this case). If the Reynolds number is high the stall coefficient of lift value for a particular airfoil shape is also higher (Figure 27), therefore more leverage in the angle of attack. High Reynolds number also reduces the drag for given angle of attack (Figure 26). Figure 26: NACA 0010 Cd Graph Figure 27: NACA 0010 Cl Graph
  21. 21. 13 | P a g e 4.2.5 Angle of Attack The blade pitch is controlled to attain correct angle of attack for maximizing the lift; however the same feature can be used for safety purposes. During adverse weather condition, the blades’ angle of attack can be reduced to zero so that it generates no lift. The process is known as “featuring” as the blades allow wind to simply pass through without extracting energy from it (except the energy required to overcome the drag affects while passing over the blade). 4.3 Power Extracted Earlier we looked into the power available from the wind however, it is important to calculate how much available power is extracted by the turbine blade design to review its efficiency. Once the lift and Drag force is calculated for a given airfoil (blade cross section), experimental or computational analysis can be carried out to measure the angular velocity. Alternatively, lift and drag force can be used along with the measure RMP to work out the angular velocity and other forces acting on the blade. With the calculated values the power extracted by the wind turbine blade can be worked out using the following equation: ܲ = ܶ߱ Equation 10: Power Extracted Where ω is the angular velocity and T is the torque given by: ܶ = ‫ܨ‬ × ‫ݎ‬ Equation 11: Torque F = force, r= radius from the centre point to where the force is acting Therefore the efficiency of the wind turbine can be determined by dividing the Power extracted (PR) by the Power Available (P): ‫ܥ‬௉ = ܲோ ܲ Equation 12: Coefficient of Performance(17) The efficiency of the turbine gives us good idea on how where the turbine needs to be altered to improve the coefficient of performance but with the improvement comes’ the cost of manufacturing and maintenance. The wind turbine also ends up losing some efficiency to overcome the frictional affects and some energy is lost as heat and noise. 4.4 Acoustics & Insulation Although the energy lost in noise, heat, etc. is minor compare to the energy lost due to blade inefficiency but reducing the other losses would still improve turbines efficiency. The few major losses that are involved in most wind turbine designs are: • Frictional affects on rotating centre • Gear frictional losses • Drag force on the blades All the losses stated above either result into noise or heat transfer. As the small wind turbine can be placed on house roof top or building roof top, the constant noise from the rotating turbine blades would upset the house or building inhabitants.
  22. 22. The noise from the mechanical rotating parts can be reduced by lubricating the parts however maintenance of these parts is expensive and difficult if the wind turbine is mounted on roof top or high mast. Blade rotating through air also produces noise which the turbine blades in a cylindrical diffuser built with high acoustic material e.g. parts and blades are not the only source of noise but the electrical generator also emits noise when wire is turning in the magnetic flux area or when high voltage current is passing through the coils. This situation not only emits noise but also transfers heat to the surroundings reducing the overall efficiency of the turbine. To summarise, properly insulating the wire the turbine and lubricating the mechanical system regularly keeps the turbine efficiency high but the maintenance cost increases. 5 Generator (KE) Torque is transferred from the rotor through a connectin electricity. The shaft is either directly connected or is connected t linked to the generator. Gearbox is placed to increase the rotational speed if the rotor is not turning fast enough for the generator to produce high frequency electricity. incorporate changing gear system managed by the controlled feedback system the gear depending on the rotor speed to keep the generator speed constant. placed at the top of the tower or at the base (connect by the gears) for HAWT and at the base for VAWT. An electrical generator torque transferred by the rotor is used to rotate 5.1 AC & DC Generator An electrical generator is a device, which converts mechanica generator produces direct current. In a DC generator an e.m.f is induced whenever magnetic flux is cut by a conductorFigure 28: DC Generator rotating in a uniform magnetic field provided by permanent magnets or the coil are connected to two slip rings R brushes are pressed against the slip rings. The current is cuts the magnetic flux between two magnets according to Fleming’s right hand rule. However the current is alternating as coil is turning (cutti rings (insulted from each other), reasons we have direct current. slip rings that are always in contact with the brushes. Therefore when alternates (as it cuts the flux in brushes also alternates. Hence the reasons we have alternating current. Figure 28: DC Generator (18) The noise from the mechanical rotating parts can be reduced by lubricating the parts however maintenance of these parts is expensive and difficult if the wind turbine is mounted on roof top or high mast. Blade rotating through air also produces noise which can only be reduced by containing the turbine blades in a cylindrical diffuser built with high acoustic material e.g. foam. The mechanical parts and blades are not the only source of noise but the electrical generator also emits noise when in the magnetic flux area or when high voltage current is passing through the coils. This situation not only emits noise but also transfers heat to the surroundings reducing the overall efficiency of the turbine. To summarise, properly insulating the wires, placing the acoustics around the turbine and lubricating the mechanical system regularly keeps the turbine efficiency high but the Torque is transferred from the rotor through a connecting shaft to the genera electricity. The shaft is either directly connected or is connected through the gearbox which then is linked to the generator. Gearbox is placed to increase the rotational speed if the rotor is not turning to produce high frequency electricity. Some wind turbine incorporate changing gear system managed by the controlled feedback system, i.e. it would change the gear depending on the rotor speed to keep the generator speed constant. placed at the top of the tower or at the base (connect by the gears) for HAWT and at the base for An electrical generator is used to convert mechanical energy into electrical energy. is used to rotate acoil of wire or a magnet to generate electricity. AC & DC Generator An electrical generator is a device, which converts mechanical energy into electrical energy. generator produces direct current. In a DC generator an e.m.f is induced whenever magnetic flux is : DC Generator (Figure 28). Figure below shows a copper conductor loop rotating in a uniform magnetic field provided by permanent magnets or electromagnets. the coil are connected to two slip rings R1 and R2 which are insulated from each other. Two collecting brushes are pressed against the slip rings. The current is induced in the coil ABCD when it rotates and between two magnets according to Fleming’s right hand rule. However the current is alternating as coil is turning (cutting the flux in two directions), but because of the split slip (insulted from each other), the current passed to the brushes is always direct For the AC generator, the coil is connected to the individual circular slip rings that are always in contact with the brushes. Therefore when the current in the coil alternates (as it cuts the flux in two direction due to its circular motion), the current passed to the brushes also alternates. Hence the reasons we have alternating current. (18) Figure 29: AC Generator 14 | P a g e The noise from the mechanical rotating parts can be reduced by lubricating the parts however maintenance of these parts is expensive and difficult if the wind turbine is mounted on roof top or can only be reduced by containing foam. The mechanical parts and blades are not the only source of noise but the electrical generator also emits noise when in the magnetic flux area or when high voltage current is passing through the coils. This situation not only emits noise but also transfers heat to the surroundings reducing the overall s, placing the acoustics around the turbine and lubricating the mechanical system regularly keeps the turbine efficiency high but the g shaft to the generator which generates gearbox which then is linked to the generator. Gearbox is placed to increase the rotational speed if the rotor is not turning Some wind turbine would also , i.e. it would change the gear depending on the rotor speed to keep the generator speed constant.Generators can be placed at the top of the tower or at the base (connect by the gears) for HAWT and at the base for convert mechanical energy into electrical energy. The re or a magnet to generate electricity. l energy into electrical energy. DC generator produces direct current. In a DC generator an e.m.f is induced whenever magnetic flux is Figure below shows a copper conductor loop electromagnets. Two ends of which are insulated from each other. Two collecting in the coil ABCD when it rotates and between two magnets according to Fleming’s right hand rule. However the ecause of the split slip lways direct. Hence the For the AC generator, the coil is connected to the individual circular the current in the coil two direction due to its circular motion), the current passed to the : AC Generator (19)
  23. 23. 15 | P a g e 5.2 InductionGenerator Electricity can also be generated by rotating magnet and fix stator with coils to induce current in. Induction generator uses principle from induction motor where the wind turbine rotor blades are connected to the magnet that rotates between a stator with coils wounded around the stator. When the magnet rotates it creates flux in the stator which cuts the coils and generates voltage (Figure 30). The magnet then turns to change the magnetic field and the flux direction which sets the scenario for changing flux between fixed coils resulting in alternative current produced. Figure 30: Induction Generator (20) 5.3 Generator types 5.3.1 Synchronous Generator (SG) The synchronous machine uses separately excited windings in the rotor in order to excite the magnetic field in the rotor. Separate excited windings give the possibility to change the output voltage by adjusting the excitation of the magnetic field of the rotor. Since the stator windings do not have to carry the power to excite the rotor magnetic field, a reduction in mass of the active materials, over the IM (induction motor), is possible. Another advantage over the IM is that smaller power handling equipment, like converters, can be used to control the SG (21). Figure 31: Synchronous Generator 5.3.2 Permanent magnet synchronous Generator (PMSG) When the separate excitation of the synchronous generator is done by permanent magnets (PM’s) instead of windings, the machine is called a permanent magnet synchronous generator. No power is lost to excite the rotor magnetic field through windings and efficiency will increase compared to the SG. Also a weight reduction can be made over the SG. Since the rotor construction of the PMSG is smaller than the rotor construction of a SG made with excitation windings .The cost reduction of a PMSG over a SG will not be proportional with the reduction in mass, since PM material is much more expensive than copper and steel used in SG rotor constructions. However the total costs for a PMSG are lower than for a SG(21).
  24. 24. 16 | P a g e Figure 32: PMSG 5.3.3 Switched reluctance generator (SRG) In a switched reluctance machine only the stator windings are excited and produce a magnetic field. The rotor is constructed in such a manner that by moving it, the rotor causes a change of stored magnetic energy in the machine. By sequentially exciting the stator coils the torque can be produced or electricity can be generated. The benefits of the SRG lie in a simple and low cost and rigid construction. However as with an IM the SRG draws its excitation magnetic field from the power source, therefore larger converters are needed to operate a SRM. For equal efficiencies the SRG construction appears to be more compact and slightly lighter than the IM construction(21). Figure 33: SRG 5.4 Permanent magnet generators Small scale wind power requires a cost effective and mechanically simple generator in order to be reliable energy source. The use of direct driven generators instead of geared machines reduces the number of drive components, which offers the opportunity to reduce the number of drive components. Also it offers the opportunity to reduce the costs and increase system reliability and efficiency. For such applications, characterized by low speed is particularly situated, since it can be design with a large pole number and high torque density. The most efficient type of generators matching the above criteria is the permanent magnet generators. So the group have decided to consider permanent magnet generators for the design(21). The permanent magnet synchronous generators are constructed in different ways. Two design characteristics of a construction type are:
  25. 25. 17 | P a g e • The orientation of the magnetic flux within the machine. • The type of rotor construction with permanent magnets. 5.4.1 The magnetic flux orientation (Radial Flux or Axial Flux) Air gap orientation can be identified in two different ways. The radial flux design magnetic field is given a radial direction by mounting the stator around the rotor. Figure 34 shows the cross sectional view in radial direction and in axial direction. The axial flux design (See Figure 35) is constructed by placing stator and rotor in a way that the air gap is perpendicular to the rotational axis, where the magnetic flux crosses the air gap is in axial direction. The axial design used in situations where the machines axial dimension is more limited than the radial dimensions(21). Figure 34: Cross Sectional View in radial direction and in axial direction Figure 35: Cross Sectional view in radial direction and in axial direction 5.4.2 Longitudinal or Transversal (Figure 5.4.1) Figure 36: Transversal Flux PMSG Transversal flux machines are manufactured by mounting the plane of flux path perpendicular to the direction of rotor motion. The transversal flux machines can used in applications where required high
  26. 26. 18 | P a g e torque density requirements. The transversal flux machines can independently adjust the current loading and the magnetic loading. The main disadvantage of transverse PMSG is that high leakage flux results in poor power factor; this can be avoided by reducing the number of poles where in turn reduces torque density. Another drawback in rotating transverse PMSG is the mechanical construction is weak due to large number of parts(21). 5.4.3 Inner Rotor or Outer Rotor The common rotor topology is acquired by mounting the PM’s on the rotor surface. This is called a surface mounted permanent magnet rotor construction. This construction requires to shape the magnets in a circular arrangement. There are two types of rotor magnetic inner rotor and outer rotor. The outer rotor machines are constructed by placing the rotor surrounds the stator. The magnets are mounted on the inner circumference of the rotor. In the outer rotor machine the rotor has higher radius compared with the stator and it can be equipped with higher number of poles for the same pole pitch. Another advantage is that the magnets are well supported despite the centrifugal force also a better cooling of magnets is provided. Figure 37 shows an inner rotor PMSG and an outer rotor PMSG(21). Figure 37: Inner rotor PMSG (left) and an outer rotor PMSG (right) (ref3) 5.5 Coil winding arrangements Winding arrangement determines the way the coils are arranged. Coil can either have an air gap or they can be placed in slots around the teeth in the stator. Density of coil taps is a choice between higher amounts of coils placed densely in one place or lower number of taps placed around the device. When and design with number of slots is considered, the choice or number of poles and coils is a choice(21). 5.5.1 Coil placement Figure 38: Slotless Design Slotless design is where the coil is placed in the air gap. This air gap increases the distance between stator and the rotor increasing the reluctance causing increase in PM (Permanent Magnet) leading to
  27. 27. 19 | P a g e a reduction in flux density. More magnetic material or copper winding are needed to compensate this. A slotless design has less steel and therefore less hysteresis and Eddy current losses. The power density of a slotless design is three times lower than in a slotted design(21). 5.5.2 Coil winding distribution In a slotted stator, the stator windings can be placed as concentrated coils around the teeth or the windings can be distributed in the slots. Concentrated coil constructions have the advantage of a higher winding factor; this increases the amplitude of the induced output voltage. Less copper is required due to shorter end windings. They are also easier to manufacture through modern automated techniques. The disadvantage of concentrated coil windings is the increase of harmonic components in the air gap flux. This causes an increase of losses in the rotor magnets and back iron due to Eddy currents(21). 5.5.3 Pole slot combinations The number of stator slots (Ns) and the number of magnet poles (Nm) that can be used in an electrical machine design are countless. For a 3 phase machine using concentrated coils, the number of combinations (Ns and Nm) is still large. Therefore the choice of slot pole arrangements has to be made by considering different slot pole combinations. The combination of 3 coils around 3 teeth with 2 magnet poles creates the lowest Eddy current losses in the magnets and rotor back iron; however this combination has a poor winding factor. Low rotor Eddy currents cause less temperature rise in the magnets, which will enhance efficiency and decrease the risk of demagnetizing the magnets(21). 6 Advantages and Disadvantages of Wind Turbine Designs (MT) As mentioned earlier, a wind turbine extracts the wind power to generate electricity. The blades extract energy from the moving wind which spins a shaft, which connects to a generator that supplies an electric current. Today there are two basic types of wind turbines available in the market. Most commonly used in wind energy systems are the traditional farm styled, horizontal-axis turbines.Vertical turbine is relatively new design that’s gaining market share rapidly. They both have their advantages and disadvantages. 6.1 Horizontal Axis Wind Turbines Figure 39: HAWT 6.1.1 Advantages of Horizontal Axis Wind Turbines • Variable blade pitch, which gives the turbine blades the optimum angle of attack. Allowing the angle of attack to be remotely adjusted gives greater control, so the turbine collects the maximum amount of wind energy for the time of day and season.
  28. 28. 20 | P a g e • The tall towers allow access to stronger wind in sites with wind shear. In some wind shear sites, every ten meters up, the wind speed can increase by 20% and the power output by 34%. • High efficiency, since the blades always moves perpendicularly to the wind, receiving power through the whole rotation. In contrast, all vertical axis wind turbines, and most proposed airborne wind turbine designs, involve various types of reciprocating actions, requiring aerofoil surfaces to backtrack against the wind for part of the cycle. Backtracking against the wind leads to inherently lower efficiency. 6.1.2 Disadvantages of Horizontal Axis Wind Turbines • Taller masts and blades are more difficult to transport and install. Transportation and installation can now cost 20% of equipment costs. • Stronger tower construction is required to support the heavy blades, gearbox, and generator. • Reflections from tall HAWTs may affect side lobes of radar installations creating signal clutter, although filtering can suppress it. • Mast height can make them obtrusively visible across large areas, disrupting the appearance of the landscape and sometimes creating local opposition. • Downwind variants suffer from fatigue and structural failure caused by turbulence when a blade passes through the tower’s wind shadow (for this reason, the majority of HAWTs use an upwind design, with the rotor facing the wind in front of the tower). • They require an additional yaw control mechanism to turn the blades toward the wind. (22) 6.2 Vertical Axis Wind Turbines Figure 40: VAWT An increasing number of progressive organizations are adopting Omni-directional VAWTs because of their aerodynamic performance advantages with characteristically turbulent and moderate winds in densely populated urban settings. VAWTs operate quietly, deliver clean electricity directly to the owner, and can feed excess electricity into the local power grid, which can further reduce the owner’s energy consumption costs. The use of VAWTs to produce distributed energy also reduces both the need for unpopular transmission lines and emissions from fossil-fuel-fired generators that contribute to climate change, and it provides points for LEED certification (Leadership in Energy and Environmental Design). Wind flow within urban and suburban environments is turbulent and veering. Increased turbulence levels yield greater fluctuations in wind speed and direction. Unlike a traditional horizontal axis wind
  29. 29. 21 | P a g e turbine (HAWT), a VAWT rotates around the shaft vertically. VAWTs provide good performance in urban and suburban environments due to their inherent design characteristics. 6.2.1 Advantages of Vertical Axis Wind Turbines • Ability to effectively capture turbulent winds which are typical in urban settings, especially in built-up areas. • No need for a yaw mechanism to face the blade rotor into veering wind directions; VAWTs therefore have higher efficiency and no orientation parts to maintain. • Operation at lower rotational speeds, thereby reducing or eliminating turbine vibration and noise. • Durability and reliability working in multi-directional wind. • Easier and less expensive repair and maintenance with generator on rooftops. • Lower noise and vibration. (23) 6.2.2 Environmental Benefits Noise & Vibration: Although urban settings are inherently noisier than rural areas, an additional noise can affect a small minority of people. A popular concern with the use of large-scale wind turbines for power generation is noise. The majority of large HAWT noise is generated from the gearbox and the aerodynamic noise of the blades. With small-scale VAWT’s, however, a gearbox is not required, and VAWT blade speeds are much lower than small HAWTs, so noise is also much lower. In a 2007 test by McMaster University, a small VAWT was tested for noise generation, which revealed that the overall noise level of the turbine remains below 50 decibel (dB) for all normal operating conditions (the turbine rarely operated at a wind speed beyond 15 m/s). When this range is converted to the dBA scale, based upon the average human hearing capability, the level drops to 20 dBA. This is because the majority of the turbine noise is produced in the infrasound range (frequencies below human perception), which is quieter than a whisper. Ultimately, the test determined that the noise level produced by the small VAWT is insignificant and poses no threat to the comfort of nearby persons or wildlife (24). 6.3 Comparison between Vertical designs Vs. Horizontal designs • A VAWT can receive winds from any direction, this is important in locations where winds Are turbulent, gusty and constantly changing directions. There is no ‘down-time’ as the rotor does not have to yaw to face the wind, in addition there are no gyroscopic effects preventing yaw. The more obstacles (e.g. trees and buildings) in your environment the more turbulent the wind is likely to be. • Aerodynamic noise is primarily generated by the fast moving tips of the blades through the air. A VAWTs tips are much closer to the axis of rotation and therefore moving more slowly through the air. • A VAWT for the same swept area has a smaller plan area than a HAWT, making it more space efficient, an important consideration when siting close or onto buildings • Loads are more evenly distributed with a VAWT than a HAWT which results in lower vibration making VAWTs a better option for roof mounts. VAWTs HAWTs Effective in laminar winds (1) Yes Yes Effective in turbid urban winds (2) Yes No Effective in low mountings Yes Sometimes
  30. 30. 22 | P a g e Ground mounting Yes No Rooftop mounting Yes Sometimes Table 1: VAWT vs. HAWT 1) Laminar: fluid air flow which occurs in "sheets" parallel to each other. 2) Turbid: flow that changes directions quickly and often and has turbulences. (25) 6.4 Justification for design choice Wind turbine we are designing would be a horizontal axis wind turbine. Even though the vertical axis wind turbines are efficient they are complex and cost of manufacturing is higher. Also since horizontal axis wind turbines been around for a long time, finding necessary component from suppliers is easy and also performance information is readily available. 7 Wind Turbine Power Management (MH) Once the energy from the wind has been harvested through the turbine blades and transmitted through a generator to produce electricity, a power management system needs to be put in place in order to ensure its intended purpose is served. This management system would have slight variations depending on the scale of the wind turbine. However, the intended final aim is to provide adequate electricity to a household power grid. Figure 41 provides an example of a typical management system that can be used for a wind turbine. Figure 41: Wind Turbine Electricity Power Management (26) Once the electricity generation process has been completed, it is then sent down through wires to a transformer unit which increases the voltage up to a few 1000 kV depending on the scale of the wind turbine. The transformer is needed for either on-shore or off-shore wind turbines where the electricity generated needs to travel a large distance. Depending on the type of generator used within the turbine, it will produce either AC or DC power. An inverter is used in order to convert from DC to AC for domestic use. The electricity can now be connected directly to the national grid network, stored in batteries for future use or connected to a household mains grid. When connecting to a household main’s grid, another transformer would be used to reduce the voltage to 120/240 V AC.
  31. 31. A small scale wind turbine to be used for domestic purposes will contain slight variations to be more suited for the purpose. Figure 42 turbine. Due to various design and build limitations in small scale wind needs to be put in place to provide safe power that can be used in a home system. Typically, they do not have variable pitch rotor blades and due to this, the rotor speed would constantly change according the change in wind speed. This does not present a favourable situation for the power management system because the output voltage and frequency provided by the generator is proportional to the speed of the rotor while the current produced is proportional to the torque on the rotor shaft. Once the electricity is generated, it is sent through a rectifier in order to convert the AC current produced through the generator. This is done because AC constantly changes direction while DC maintains a single direction, thus making sent to a Voltage Regulator unit which is used to maintain the voltage at a constant level independent of the variability presented to the system. This regulator system can also ensure that the voltage supplied is at the correct frequency and phase. The system is then taken over by a DC control unit which works in a similar method to an Engine Control Unit (ECU) in a vehicle. Now that we have a constant voltage supply which is regulated, we can distribute the electricity using various methods. The electricity could be stored within batteries for future use. If it is required to be used within a household grid, an inverter would be used to convert DC to AC which can then be distributed. Another opti excess electricity back to the national grid which could help recuperate some of the costs of the system. Such systems however would need to be agreed to by the supplier and considerations would need to be made if it would be better to store excess electricity within batteries or to sell back to the grid, where once sold, if the wind turbine does not produce enough electricity, cost of purchasing the same amount would be higher. 8 Safety Systems for Wind Turbines A typical wind turbine is designed to operate for a lifespan of around 20 years. Within this period, it is expected for it to be operated under various weather conditions which can often be unfavourable. A wind turbine has a design operating condition whi stopped in order to prevent damage. Therefore various safety systems are put in place to prevent damage to the turbine or people who are within the vicinity of the turbine. 8.1 Vibration Sensors During adverse weather conditions, vibration of the turbine can be dangerous for the turbine itself and the parts contained within it. These can range from a very basic mechanical sensor which works wind turbine to be used for domestic purposes will contain slight variations to be more 42shows a typical system which might be used for a household wind Figure 42: Small Scale Wind Power (27) Due to various design and build limitations in small scale wind turbines, a few additional systems needs to be put in place to provide safe power that can be used in a home system. Typically, they do not have variable pitch rotor blades and due to this, the rotor speed would constantly change nd speed. This does not present a favourable situation for the power management system because the output voltage and frequency provided by the generator is proportional to the speed of the rotor while the current produced is proportional to the torque on Once the electricity is generated, it is sent through a rectifier in order to convert the AC current produced through the generator. This is done because AC constantly changes direction while DC maintains a single direction, thus making it easier to regulate. Once this current is converted, it is sent to a Voltage Regulator unit which is used to maintain the voltage at a constant level independent of the variability presented to the system. This regulator system can also ensure that oltage supplied is at the correct frequency and phase. The system is then taken over by a DC control unit which works in a similar method to an Engine Control Unit (ECU) in a vehicle. Now that we have a constant voltage supply which is regulated, we stribute the electricity using various methods. The electricity could be stored within batteries for future use. If it is required to be used within a household grid, an inverter would be used to convert DC to AC which can then be distributed. Another option available for home owners is to sell excess electricity back to the national grid which could help recuperate some of the costs of the system. Such systems however would need to be agreed to by the supplier and considerations would would be better to store excess electricity within batteries or to sell back to the grid, where once sold, if the wind turbine does not produce enough electricity, cost of purchasing the Safety Systems for Wind Turbines (MH) A typical wind turbine is designed to operate for a lifespan of around 20 years. Within this period, it is expected for it to be operated under various weather conditions which can often be unfavourable. A wind turbine has a design operating condition which once exceeded, would require it to be stopped in order to prevent damage. Therefore various safety systems are put in place to prevent damage to the turbine or people who are within the vicinity of the turbine. conditions, vibration of the turbine can be dangerous for the turbine itself and the parts contained within it. These can range from a very basic mechanical sensor which works 23 | P a g e wind turbine to be used for domestic purposes will contain slight variations to be more a typical system which might be used for a household wind turbines, a few additional systems needs to be put in place to provide safe power that can be used in a home system. Typically, they do not have variable pitch rotor blades and due to this, the rotor speed would constantly change nd speed. This does not present a favourable situation for the power management system because the output voltage and frequency provided by the generator is proportional to the speed of the rotor while the current produced is proportional to the torque on Once the electricity is generated, it is sent through a rectifier in order to convert the AC current produced through the generator. This is done because AC constantly changes direction while DC it easier to regulate. Once this current is converted, it is sent to a Voltage Regulator unit which is used to maintain the voltage at a constant level independent of the variability presented to the system. This regulator system can also ensure that The system is then taken over by a DC control unit which works in a similar method to an Engine Control Unit (ECU) in a vehicle. Now that we have a constant voltage supply which is regulated, we stribute the electricity using various methods. The electricity could be stored within batteries for future use. If it is required to be used within a household grid, an inverter would be used to on available for home owners is to sell excess electricity back to the national grid which could help recuperate some of the costs of the system. Such systems however would need to be agreed to by the supplier and considerations would would be better to store excess electricity within batteries or to sell back to the grid, where once sold, if the wind turbine does not produce enough electricity, cost of purchasing the A typical wind turbine is designed to operate for a lifespan of around 20 years. Within this period, it is expected for it to be operated under various weather conditions which can often be unfavourable. ch once exceeded, would require it to be stopped in order to prevent damage. Therefore various safety systems are put in place to prevent conditions, vibration of the turbine can be dangerous for the turbine itself and the parts contained within it. These can range from a very basic mechanical sensor which works
  32. 32. 24 | P a g e by having a ball resting on a ring where the ball is connected to a switch through a chain. If vibrations reach an excessive limit (which can bet set at a required amount), the ball will fall out of the ring which would enable to switch to turn off the turbine. Advanced electronic sensors which are connected to the electronic control system of the turbine could also be employed to monitor vibration levels. 8.2 Turbine over-speed Since the turbine blades would rotate faster with increasing wind speed, it has a safe limit of operation. This limit is set to ensure there would be no blade failure and also protects the components within the nacelle such as generators and gearboxes from overheating and eventual failure. Modern wind turbines are equipped with variable pitch controlled blades where the optimum pitch is constantly selected in order to gain the maximum power output. In an event of high wind speeds, the pitch control would turn the rotor blades 90 degrees (aerodynamic braking). This creates an aerodynamic effect which gently brings the turbine to a stop within a few rotations. The major advantage of this system is that it does not present major stress factors on the system and once the high wind speeds are over, the pitch control will take over once again to make the rotor turn. A mechanical braking system is kept in place as a backup to the aerodynamic braking system when required. This system is similar to the disc brake system used within cars where a disc rotates with the shaft and a brake pad is activated in case it is necessary to stop. This system can also be used as a parking brake when maintenance is needed. 8.3 Thermal and other sensors The nacelle of the turbine houses some of the most important components of a turbine. These include the Shaft, Gearbox, Generator, etc. Advanced sensors which monitor the temperature and pressure among many other parameters constantly feed information into the electronic control system of the turbine which would detect any abnormalities and determine if a system shut down is necessary. Overheating can present numerous problems to a turbine because this can lead to fire, additional stress placed on components and bearings, etc. 8.4 Anti-Icing Systems A wind turbine’s blades are constantly exposed to the environment which requires it to withstand large variations in temperature. A significant problem in wind turbine operation is having ice build-up within the blades. While building up of ice can present a danger of the ice falling once the turbine is operational, it also presents challenges to its efficiency due to ice formation changing the shape of the aerofoil shape of the blades. Blade design is a carefully researched area and this change in shape due to ice can reduce its operating efficiency while presenting dangers to people below. Many modern turbine blades have systems to deal with such situations. Parent and Ilinca (28)conduct a thorough review of the current systems that exist for anti-icing and de-icing systems. These include a special coating to prevent the formation of ice and a super-hyperbolic coating which does not allow water to remain on the surface. Other systems include inducing heat in order to prevent the ice build-up. 8.5 Material Failure Material selection is extremely important in the design of a wind turbine due to its operating conditions. Testing of this material is also important in order to determine the effects that are present during high levels of loading. A recent report by Elforsk (29)provides a thorough guidance of damage prevention to many parts inside the nacelle (primary/secondary shafts, rotor hub, bolts, gearboxes, bearings etc.). Many failures are attributed to fatigue or corrosion and recommendations are made regarding various testing methods that can be employed (Eddy Current, Magnetic Particle,
  33. 33. 25 | P a g e Sonic, Termographic etc.). Therefore the timely testing and observation to such damage could prevent incidents such as a blade failure, gearbox failure etc. 9 Manufacturing Methodology and Processes (MH) 9.1 Design for Manufacture/Design for Assembly Modern product development states that a product should not only be ‘simply designed’. It should also consider the path the product would take through its manufacturing, assembly, disassembly and finally through servicing of the product. In their book, Kalpakjian and Schmid (30) mention that design and manufacturing must be intimately interrelated. They argue that we should not view these two as separate identities but two that must go hand in hand. When any design process is undertaken, it is vitally important to do so for each part and component which would also reap its benefits economically. This would also allow the company to standardise its manufacturing process so that productivity can be improved. Employing Lean Six Sigma (discussed in a later section) is another popular and effective method of achieving maximum productivity for a process. Although initial costs may be incurred to implement six sigma methods and techniques, many companies large and small, have achieved significant increases in productivity and efficiency along with long term cost savings. This concept is known as Design for Manufacture (DFM). Kalpakjian and Schmid (30)further highlight that DFM is a comprehensive approach to the production of goods, and it integrates many design features which should take into consideration the materials, manufacturing methods and processes among many others. This requires that the designer have a fundamental understanding of such processes and specifically for DFM, about various machining processes and equipment. If a designer wants to have a successful product, he/she should also understand the effects of machining too. These include surface finish, accuracy of each machining process, processing time etc. An extension from DFM is DFA (Design for Assembly), which constitutes the next step after the manufacture of individual components. When considering cost of operating a business, the efficiency of the assembly process is critical to overall costs associated for the product. If DFA methods are applied to a product design, then it would consider the ease, speed and cost of assembling the parts together. The ease of assembly would be considered at a design stage because the easier it is to assembly, the quicker it would be which would save precious time of the employees. If would contribute to the bottom line of the business enabling to produce more units within a given period of time. DFM and DFA can be combined as a methodology named DFMA (Design for Manufacturing and Assembly). DFMA can now benefit from advanced computer software that would help the designer from the very beginning of the process. Modern designers use Computer Aided Design (CAD) software which can now aid them to use DFMA effectively. Greenlee defines the cost split for DFMA as 70% for design decisions (Cost of materials, processing, and assembly), 20% for production decisions (process planning and tooling selection) and the remaining 10% other costs. Greenlee also gives a comprehensive 10-step guideline for DFMA which summarises the whole process. They are given below: 1. Reduce the number of parts 2. Develop a modular design 3. Use of standard components 4. Design parts to be multi-functional 5. Design parts for multi-use 6. Design for ease of fabrication 7. Avoid separate fasteners

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