Table of Contents
CHAPTER ONE.. 5
Reasons and Relevance of the Project 5
Aims of the project 5
Background Research. 6
Timescales and provisional work plan. 7
CHAPTER TWO.. 8
Literature Review.. 8
Theory behind wind turbine farms. 8
How does it work. 10
Betz limit 10
Relation between the high of the tower and the length of wind turbine. 11
Lift Force and Drag Force. 11
Lift Force. 12
Drag Force. 12
Calculation of Lift and Drag Forces. 14
Calculation of Total Force and torque. 14
Electricity demand. 15
Different types of wind turbines. 16
Horizontal axis wind turbines (HAWT) 16
Upwind Turbine. 16
Downwind Turbine. 17
Vertical Axis Wind Turbines (VAWT) 17
Darrieus Turbine. 17
Giromill Turbine. 18
Savonius Turbine. 19
Operation and maintenance (O&M) costs. 20
CHAPTER THREE.. 21
Infrastructure Details. 21
Civil Works. 21
Mechanical works. 21
Electrical works. 22
Computer Software. 22
Assembly and installation of wind turbines. 23
What is next 24
Figure 1: Parts of wind turbineÂ 9
Figure 2: Shows the wind energy conversion percentageÂ 11
Figure 3: Stationary object’s Lift and DragÂ 13
Figure 4: Diagrams showing Lift and Drag of wind turbine rotor bladesÂ 13
Figure 5: Upwind Wind TurbineÂ 16
Figure 6: Downwind Wind TurbineÂ 17
Figure 7: Darrieus Wind TurbineÂ 18
Figure 8: Helical Giromill Wind Turbine& Figure 9:Giromill Wind TurbineÂ 19
Figure 10: Savonius Wind TurbineÂ 19
List of Equations
Equation 2. 13
Equation 3. 13
Equation 4. 13
Equation 5. 14
The wind as a source of energy is plentiful and clean. The Canadian Wind Energy Association (CanWEA) for example estimated that energy from wind could supply to about 205 MWh of electricity needs of Canada. Electricity generating from wind turbines are in different forms and sizes for instance big wind turbines set up in clusters referred to as wind farms which can produce large electricity amounts. The principle of the operation is based upon converting wind energy into kinetic energy used to turn the blades of the wind turbine. According to (Rehman, 2004) Germany was on the top list of 45 countries in the world that utilised wind power in producing electricity. However, important assessments should be followed in order to get the technology operated efficiently in a location by having wind parameters analysis and statistics for that location before starting such project. These statistics include statistical characteristics, persistence, availability, diurnal variation, and prediction of wind speed (Rehman, Halawani & Muhandes, 2003).
In order to consider such a project commercially, the wind farm should be large so that the whole will be spread over the investment. The following table shows the cost breakdown for a 10MW wind farm (Burton etal, 2001, p.511).
|Elements of wind farm||% of the cost|
|Wind farm electrical infrastructure||8|
|Electrical network connection||6|
|Project development and management cost||8|
The change in the global climatic conditions due to the utilization of non-renewable energy sources has prompted states to adopt renewable energy sources. The past ten years have seen the sudden upsurge of wind energy, producing close to 121.2 GW (Munday, Bristow & Cowell 2011). The production of electrical energy from wind energy is done by wind turbines, grouped into farms to ensure high-efficiency levels by reducing the installation and maintenance costs (Coleman & Provol 2005). It also aims to promote environmental conservation since unlike other power plants; it produces zero emissions to the atmosphere that in the end promote global warming (Coleman & Provol 2005). Additionally, wind energy ensures maximum utilization of land because ranchers and farmers will have zero interruptions in their daily activities.
This project aims to design a Wind Turbine farm. The following objectives will be used in order to achieve the aim.
- Design a wind turbines farm which contains five wind turbines
- Choose a specific area in King Saudi Arabia to apply the design
- Study the mechanical works need to implement the design
- Study the electrical works need to implement the design
- Study the civil works involved in the design
1.4 Background Research
Various project and research have been carried out on the generation of electrical power from wind energy. Some of the countries that utilize wind power for the generation of electrical energy include Australia, India, Japan, Canada, Pakistan, European Union, America, and South Africa (Coleman & Provol 2005). Their choice of wind turbines is influenced by the direction of the wind, wind speed, the amount of power to be generated, and nature of the landscape (Benitez, Benitez & van Kooten 2008).
Close to 80 percent of the wind turbines used in electric power generation begin produce electricity at wind speeds of as low as 4 meters per seconds. Maximum production volume is achieved when the wind speeds range between 15 and 12 meters per second (Coleman & Provol 2005). Consequently, the efficiency of wind turbine is increased when the wings are rotated quickly. It is worth noting that wind turbines in residential areas are fitted with governors to ensure their rotational speed does not exceed the safety margin (Feng & Shen 2015). Studies have shown that wind turbines produce the least amount of energy emissions compared to other electrical energy generators.
Anemometer: This instrument records the speed of wind and transfers the information to the controller. Blades: They are usually two or three in most turbines and they lift and rotate as wind hits the blades thus forcing rotation of the rotor. Brake: They force the rotor to halt either hydraulically, mechanically or electrically during emergencies. Controller: it engages the machine to start when speeds of wind get to about 8 to 16 mph and also engages in shutting down at winds speeds of about 55 mph as higher than 55 mph wind speeds may damage the turbine (The British Wind Energy Association 2005). Gear box: acts as a connection between the low and high-speed shafts and raises the shaftâs speed of rotational to about 1000-1800 rotations per minute (rpm) from about 30-60 rpms which is the recommended speed for electricity production by generators. Generator: it is normally an induction generator considered as from off-the-shelf. High-speed shaft: this type of shaft is responsible for generator driving or running. Low-speed shaft: this shaft rotates at about 30-60 rpm. Nacelle: located on top of the tower andthey contain the generator, brake, gear box, high-speed and low-speed shafts and the controller. Pitch: responsible for bladesâ pitching or turning out of the wind therefore ensure rotor speed control and also ensure rotors do not turn in low or high winds which generate electricity (Sahu 2015).
Rotor: is formed by the hub and the blades. Tower: it is in charge of supporting the turbine structure and is made from steel lattice, tubular steel or concrete. More energy is captured by turbines with taller towers since speed of wind goes hand in hand with height thus more electricity generation. Wind direction: the turbine design is determined by this with downwind turbines facing away from the wind while upwind turbines face in the direction of the wind (Hristov n.d.). Wind vane: This instrument records the direction of wind and transfers the information to the yaw drive that in turn orients the turbine in relation with the wind. Yaw drive: Aligns the upwind turbine to ensure they face the direction of wind in case the wind changes. However for downwind turbines the rotor is blown away from it manually by the wind. Yaw motor: It is responsible for yaw drive powering (Sahu 2015).
- An horizontal axis wind turbine
- It has 3 blades in order to reduce the load produced on the rotor and because wind stream is mainly in line with the blade in the chosen area.
- Model is Suzlon S641.25 MW
- Blade length is 32 mÂ (105 ft)
- Hub height is 73 mÂ (240 ft)
- Tower height is 105 m (344 ft)
- Swept area by blades 3,217 m2(0.79 acres)
- RPM range 13.9/20.8156 mph
- Max blade tip speed 156 mph
- Wind speed 12 m/sÂ (27 mph)
Wind turbines use natural power from wind in production of electricity and the wind drives the generator. The number of blades can range from two, three or four but the most used are the rotors with three blades and rotation of the blades is at the towerâs top anchored at the horizontal hub (Hristov n.d.). A turning force is exerted when wind moves over the blades and the shaft located inside the necelle starts to turn as a result of the blades rotating. The shaft connects to a gearbox which connects to a generator and the gearbox through a set of gears causes an increase in speed of rotation for the generator. The generator then converts the energy of rotation into electrical energy by employing magnetic fields. The output power produced is transferred to the transformer, which then converts the generatorâs electricity from700 Volts (V) to the required distribution system voltage of between 11kV and 132kV. This electricity is then transmitted into businesses and home throughout the nation by the National Grid or the Regional Electricity Distribution networks (The British Wind Energy Association 2005).
In 1926 Albert Betz came to the conclusion that no wind turbine had a conversion rate of more than 59.3 percent of the windâs kinetic energy that is converting into mechanical energy by rotating a rotor using wind(Hristov n.d.).
The relationship between the length of the turbine and the tower follows the rule that they are directly related in that the longer the length of the wind turbine the higher the distance from the ground the tower is. The tower of the turbine needs to be high enough for two main reasons. One is the ground drag that is the friction between the earth and the masses of moving air reduces with increasing distance above the surface of the earth. Two is that the turbulence resulting from the earthâs obstacles such as buildings and trees decreases with height on top of such obstacles (Sagrillo, Power & Light 2005).
Two forces are produced when air moves over a stationary airfoil (rotor blades), where a drag force parallel to the air flow direction is produced and a lift force that is perpendicular to the direction of air flow. Both the drag and lift forces are proportional to the wind speed square, the density of air, and the airfoil (rotor blade) area (Hristov n.d.).
Lift is also referred to as downforce and refers to the force produced that is perpendicular to an objectâs travel direction that moves through a fluid (liquid or gas). When a fluid travels on top of an object that is stationary like the rotor blades of a wind turbine, this same effect happens (Symscape 2007). The occurrence of this force is highly dependent on laminar flow over the rotor blades and if turbulent flow occurs instead of laminar flow then little or no force of lift occurs. The flow of air over the top of the blade has to speed up since it has a bigger traveling distance and the rise in speed causes a small pressure reduction. The difference in pressure along the blades causes the lift force which is normally perpendicular to the air flow direction (Johnson 2001).
This is an unavoidable force resulting when an object moves through a fluid (liquid or gas) and is normally opposite and parallel to the direction of flow of the object traveling through a fluid (Hristov n.d.) . The components of drag force include: Pressure/ Form drag and this force depends on the moving objectâs shape through the fluid; and Skin friction which depends on the viscous friction when an object or moving surface travels through a fluid. This force is derivation of wall shear stress (Symscape 2007).
Nature of Drag and Lift Forces
The drag and lift forces result from difference in pressure that results when a fluid (gas or liquid) flows around a stationary object. The drag force results from the fluid friction and never amounts to zero. The values of drag and lift can be derived by integrating the values of pressure along the object surface (i.e. along the section perimeter parallel to the fluid flow) (Hristov n.d.)
Â Â Â Â Â Â Â Â
The coefficients of lift and drag are defined as (Symscape 2007):
L – Lift force
D – drag force
CL – dimensionless lift coefficient
CD – dimensionless drag coefficient
A – reference area of an rotor blade
qinf – Bernoulli’s equation free stream fluid dynamic pressure
The Bernoulli’s equation is given by:
rhoinf – density of the free stream fluid
Vinf â speed of the free stream fluid
The total force on the rotor blade is given by (Symscape 2007):
pi – pressure at the elementâs center
taui – wall shear stress at the elementâs center
Ai – element area
ni – element normal direction
i – ith element
The torque coefficient formula is given as below (Smulders 2004)
V –free stream fluid speed
Ï – air density
R â rotor radius
Q â shaft torque power
The maximum population of the region where the turbine farm is destined to be set up is about 1000 people. The number of buildings in the regions is 340 buildings and this is inclusive of houses, government offices, school, police station and middle size clinic. Most demand for electricity will be during the summer when itâs very hot and less demand during the winter. During this period that is summer time the demand per individual person could be 1 kwh. The estimated production of one wind turbine is 1.25 Mwh and this could be enough to supply the population of 1000 people, with a surplus of 0.25 Mwh. However, an extra wind turbine with the same production rate will be required for backup purposes.
This is a turbine where the axis rotation of the rotor is normally parallel to the ground and wind stream. The major occurring types of HAWT are the two or three blade but we also have some with more than or less. The main types of HAWT are the downwind and upwind types of wind turbines (Bajaro n.d.). The working mechanism of the HAWT is that wind moves over the bottom and top surface of rotor blade but the upper blade side experiences more rapid flow of air current than the down side. This creates low pressure on the upper side and thus causes an aerodynamic lift due to a difference in pressure between the two sides. The wind turbine blades are aligned to travel in a plane with a center hub therefore revolving about the hub occurs as a result of the lift force while drag force prevents the rotation of the rotor (Julia 2011). The different kinds of HAWT include:
This turbine has its rotor facing the wind and its main significance is the fact that, behind the tower it avoids the wind shade. On the contrary the major disadvantage of this is that the rotor requires to be inflexible and fixed far from the tower at a distance. This turbine requires a yaw mechanism to ensure the rotor faces the wind (Darling 2011).
This turbine has its rotor on the leeward or downwind side of the tower. Its main advantage is that it does not need a yaw mechanism since their nacelles and rotors have suitable designs that direct the nacelle to flow passively with the wind. Its rotor can also be built to be more flexible. Its major disadvantage is the wind power fluctuation resulting from rotor passing through the towerâs wind shade (Darling 2011).
The VAWT rotors rotate vertically instead of horizontally around its axis (Bajaro n.d.). It is however not as efficient as the HAWT but provides an advantage of working smoothly in low situations of wind whereas the HAWT operate in difficulty during low winds. It is also safer and easier to construct and can be placed near the ground making it better at handling turbulences than the HAWT. The drawback to this turbine is that it is normally used for private purposes as the maximum efficiency is 30% (NTNU. NTNU. 2011). The different types of HAWT include:
This turbine consists of several blades that are vertically oriented and a vertical rotor. As this rotor is not self-starting, it is started by a little powered motor. After gathering momentum, the wind moving through the blades/ airfoils creates torque therefore driving the rotor. The lift forces then powers the turbine and this forces are generated by the airfoils. Higher speeds are reached by the turbine when necessitated by the blades and this speeds are higher than the normal wind speed which makes this turbines suitable during turbulent winds for generation of electricity (Julia 2011).
These are special types of turbines discussed above that is Darrieus wind turbine. It employs a similar mechanism as the previously discussed turbine to capture energy but uses two to three blades that are straight separately connected to the vertical axis as opposed to the blades that are curved. Helical blades connected to the vertical axis can also be used and this help to reduce pulsating torque (REUK. 2007).
Source: (Bajaro n.d.) for both figures 7 and 8
This turbine is the simplest and it consists of 2-3 scoops as it is a type of drag device. Due to the curved nature of the scoop, the drag is more when traveling with the wind than when traveling against it. The drag difference forces the rotating of the Savonius turbine. These turbines produce less wind power than previous turbine types as they are drag-type turbines (REUK 2008).
These costs are the main sources of costs and are extremely vital towards proper functioning of wind turbines. The costs of operation include the wind turbine insurance costs, land rental costs, remote and on-site operations and taxes while the costs of maintenance may include components of periodic testing, routine checks, blade cleaning,changing of filters and oil, inspecting and torqueing of bolts and nuts, costs of unscheduled maintenance, periodic maintenance and electrical equipment maintenance. The costs of O&M may be classified into two main groups thatare variable and fixed costs. O&M associated variable costs include yearly costs directly associated with quantity of operation of plant activities. The O&M related fixed costs refer to the costs that have no association with the plant operation activities amount (Manwell, McGowan & Rogers 2009).
The main infrastructures required in the construction of a wind turbine farm are civil mechanical and electrical works. These are related to the engineering factors, which need to be considered when such a project is conducted, and as follows:
The wind turbine foundations should have high strength properties to support effectively the turbine under extreme loading conditions. In most cases, the design loading conditions for the foundation structure is all-out once in 55 years wind speed. In Europe and parts of Asia, this wind speed is described by the three-second gust. For this wind turbine site, the optimum wind speed is estimated to range between 50 and 65 m/s. The turbine supplier usually provides the foundation loads. A typical foundation takes a hexagonal shape, 2 meters deep and 13 meters across. To enhance its ability to withstand extreme loading conditions, reinforced concrete casts are attached to the base.
The foundation for the tower sections will be constructed using concrete. On completion, the tower sections are set in relation to the design plan (Rohatgi, AraÃºjo & Primo 2013). The rotor is then assembled before being fitted on the tower sections with the help of cranes. To increase the output voltage of the generator, a gear drive will be fitted in the generator shaft (Rohatgi, AraÃºjo & Primo 2013). Additionally, a mechanical emergency brake will be fitted to ensure that the turbine can break in time in the event of an emergency (Rohatgi, AraÃºjo & Primo 2013). The user can physically lock the rotor preventing it from turning. The brake system will be hydraulic, an improvement of the GTB hydraulic brake kit (Rohatgi, AraÃºjo & Primo 2013). To enhance the tip deflections and structural quality of the rotor, the lengths of the chords will be increased along the root and the span.
The wind turbines in the farm will be interconnected by a medium voltage electrical network whose operating range is 10-35 kV. Underground cables are often applied as they not only create great visual influence but are also cheaper (Rohatgi, AraÃºjo & Primo 2013). The use of overhead restricts the utilization of crazes during maintenance and service operations. The voltages in turbine generators usually range between 1000 and 690 V. Thus, it is essential for each turbine to have a step up transformer to increase the generated voltage before transmission.
Wind farm sites are chosen because of their potential for good and strong winds and this might act as a limitation for the operation of cranes during installation and assembly for safety reasons. Installation concepts were introduced to decrease the operation duration of installation and which were based on transporting the already assembled components (pre-assembled parts) to the site. A wind turbine includes 6 major components that is non-inclusive of transition piece and foundation, and the six parts include nacelle, three blades, tower and hub (Uraz 2011).According to Wind Endurance Power Team (2015), the stagesemployed in the assembly and installation of wind turbines include:
Step 1: Gearbox assembly building â this involves nacelle assembly which holds the blades and sits on the tower. The gearbox which is positioned at the center of the nacelle is installed through placing on the main shaft, the bearings which is then mounted on the gearbox.
Step 2: Turbine base attaching to the shipping frame âafter mounting the shaft and gearbox in position, then the turbine base is attached to the shipping frame which is made of steel which connects the nacelle during the final installation phase to the tower. Yaw system is then mounted to the mainstream and the two components are then installed to the turbine base
Step 3: Generator and gearbox mounting – the two components are then mounted to the mainframe which form the turbineâs Power Trainwhich isinstalled into the nacelle.
Step 4: Electrical controls wiring âthis stage involves the wiring of the electrical controls of the turbine. Wiring of the control cabinet of the nacelle is also done and this component is responsible for controlling the turbine.
Step 5: Dynamometer Testing âthe turbine is then tested for several hours conducting analysis in form of Dynamometer Testing. This acts as a simulation of actual conditions of operations to make sure the turbine performs correctly and in this stage 151 checks are carried out.
Step 6: Attaching the rotor hub âthis is connected to the main shaft which acts as a supporting system to the blades and nacelle. At this stage a lightning protection system is attached to the holder of the blade which protects the turbine during stormy and lightning weather.
Step 7: Nacelle cover addition âthe nacelle is then fitted with an outer cover and final touches of cleaning and polishing are done.
Step 8: Blade preparation â blade inspection is then done and after they are set for assembly and this are connected to the nacelle at the turbine installation site
Step 9: Final assembly and installation â the parts that is blades, nacelle and tower are transported to the site of installation and using cranes this components are pieced together with tower being mounted with a foundation. All parts are connected together and after installation of all parts, testing of turbine is done to ensure all parts work well is done.
- Interim report Submission
- Carry out further literature review research
- Study the swept area
- Understand further the aerodynamic thus enhance the shape blade
- Design a simple wind farmâs module
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