Wind Turbine Feasibility Report

University of Glasgow Faculty Engineering Feasibility Report for Wind Turbine on the Isle of Cumbrae Integrated System Design Project

Team Members • • • • • • • • •

Project Manager: Ikenna Ejiofor Engineering Manager: Ali Mohammed Adil Planning Manager: Yadan Rao Financial Manager: Qing Peng Quality Manager: Saeed Al Amri Construction Manager: Sundeep Kumar Operation and Maintenance Manager: Sajal Thakur Environmental Manager: Arinze Health and Safety Manager: Gao Submitted By: Team 2 Supervised By: Professor Ross Wilson

University of Glasgow 2010 Faculty of Engineering

ABSTRACT

This paper describes a feasibility study for wind turbine project on the Isle of Cumbrae, discusses its system designs and evaluates the possibility for undertaking such a large scale project which may be capable of offering long term benefits to the company, the denizens of the Island and also the environment. Based on the presently available published literature, the feasibility study performed in the report takes into account environmental, ecological and financial aspects and an extensive amount of  subjective evaluation that leads to the recommendations and a potential design for the wind turbine which. The health and safety and environmental considerations were produced as a part of the design process. Also, the Construction plan, Quality Assurance plan and the Cost and Income estimations are produced. Systems Engineering principles and methodologies along with some management principles have been used to arrive at a design and to complete the feasibility study for this project. This project concludes that building this wind turbine will be useful for the environment, feasible financially and can be further evaluated based on public opinion. The project assesses different aspects involved qualitatively and quantitatively.

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TABLE OF CONTENTS Section

1.

2.

3.

4.

5.

Description List of Figures List of Tables INTRODUCTION

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1.1. History of Wind Energy 1.2. U.K. Wind Energy 1.3. Power from the Wind 1.4. Isle of Great Cumbrae PROJECT OVERVIEW 2.1. Purpose and Scope 2.2. Report Organization SITE SELECTION 3.1. Wind Speed 3.2. Noise 3.3. Environmental Impact 3.3. 1. Wildlife Impacts 3.3. 2. Impacts on Historical, Archaeological & Cultural 3.3. 3. Visual & Aesthetic Impacts 3.3. 4. Environmental Interference 3.3. 5. Sore conclusion 3.4. Accessibility 3.5. Smart Analysis TURBINE STRUCTURE SELECTION 4.1. Cost-benefit Tradeoffs 4.2. Design Standard 4.3. Demand on the Isle of Great Cumbrae 4.4. Access to Transmission Lines & National Grid 4.5. Decision Point TURBINE SYSTEM DESIGN 5.1. AERODYNAMIC SYSTEM 5.1. 1. Wind Use & Wind 5.1. 2. Rotor Design 5.2. MECHANICAL SUBSYSTEM 5.2. 1. Yaw System 5.2.1.1. Yaw Bearings 5.2. 2. Pitch System 5.2.2.1. Pitch Control 5.2.3. Operating conditions and bearing dimensions 5.2.3.1 .Bearing Load 5.2.3.2. Brake System 5.2.4. Gearbox for wind turbine 5.2.4.1 . Types of Gearbox 5.2.4.2 . Advantage of Planetary Gearbox 5.2.4.3 .Materials Used 5.2.4.4. Gear box specifications 5.2. 5. Shaft

6 6 7 7 8 8 8 10 10 11 11 11 12 12 12 12 12 13 14 14 14 15 15 15 17 17 17 18 19 19 19 21 21 22 22 22 23 23 23 24 24 25 2

5.3.

ELECTRICAL SUBSYSTEM 5.3. 1. Realistic Calculation 5.3. 2. Grid Connectivity 5.3. 3. Connectivity Scheme 5.3. 4. Technical Specification 5.3. 5. Protective equipment 5.4. CONTROL SUBSYSTEM 5.4. 1. Control System Definition 5.4. 2. Cut-in & Cut-out Wind Speed 5.4. 3. Summary 5.4. 4. SCADA System 5.4.4.1. Communication Media 5.4. FOUNDATION SUBSYSTEM 5.5. 1. Construction of Foundation 5.5. 2. Foundation Design 5.6. TOWER LAYOUT 6. ENVIROMENTAL IMPLICATIONS 6.1. Proposed Development 6.2. Environmental Impact Assessment 6.3. Lifecycle Assessment 6.4. Energy Balance 6.5. Sustainability 6.6. Wind turbine Disposal & Cost 7. HEALTH & SAFETY PLAN 7.1. Accident and fatality rates 7.2. Community safety assessment 7.2.1. Wind turbine system protection 8. QUALITY ASSESSMENT PLAN 9. CONSTRUCTION PLAN 9.1. Site clearance 9.2. Access routes 9.3. Construction scheme 10. FINANCIAL FEASIBILITY OF WIND TURBINE 10.1. Cost estimation 10.1.1 Initial Capital Cost 10.2. Net Income 11. ECONOMIC ANALYSIS 11.1. Simple payback 11.2. Life cycle cost 11.3. Cash flow 11.4. Conclusion 12. SUMMARY AND RECOMMENDATION Annexure References

25 27 28 29 31 32 32 33 33 33 33 33 34 34 35 36 37 37 37 40 40 41 42 44 44 44 44 48 50 50 51 51 53 53 53 56 58 58 58 58 59 60 61-75 76-79

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LIST OF FIGURES: A typical spread footing foundation Annual wind speed at 80meters height at Isle of Cumbrae Braking system Connection point distance and position from site location Construction plan flowchart aerial view of site location Control mechanism for wind turbine Control schematic Delivery point view Final location Force components Gearbox Generator Global wind energy council 2007 press release on world resource use Inverter Low speed end and high speed end shaft Mechanical pressure vs. RPM standards Pitch system being required Power rectifier Primary locations based on high wind speeds Rectifier Report structure/flow chart Risk assessment due to icing conditions SCADA control Self serving portable toilet Sound power vs rated power The wind turbine control subsystem block diagram Tower schematic Turbine design schematic Turbine site across the road Wind rose for western Scotland Wind speed vs. power generated Yaw bearing being mounted Yaw bearing of typical 5MW turbine Yaw drive Yaw system mechanism LIST OF TABLES: Balance of station cost Cash flow over the life of the turbine Designing Labour cost Details of gearbox being used Electrical parts Existing rotor diameter from leading companies HP and gearbox ratio relationship rel ationship 4

Initial capital cost of wind turbine Maintenance scheduling (tentative) Net present value of net annual income Power and extractable energy values Removal scenario for materials SMART analysis: rating each site location Smart analysis: weighted analysis of site location Speed, RPM and shaft diameter relationship Summary of global values for renewable sources Turbine system cost V82- 1.65MW Wind speed and power Yaw bearing dimensions and materials properties Yaw bearing duty cycle

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1. INTRODUCTION 1.1. History of Wind Energy

The use of wind as a resource dates back to Persia in the 500 A.D. when it was used for grain grinding and water pumping (Early history through 1875, 2001). Since then its development and the investment in its research and procurement has been exponential. However, most of this technological advancement in the field took place after a period of stunted growth in the 1960’s due to availability of  cheap petroleum. The depleting non-renewable sources brought wind back to the centre stage of  research and its development was rapid (Early history through 1875, 2001). 1.2 UK Wind Energy

The Global Status Report in 2009 on Renewable Energies by Renewable energy policy network takes an optimistic stance towards growth in this sector when it is guided through policy driven, stable and predictable governmental strategies in spite of the recent global financial crisis (Global status report, 2009) and the Global Wind Energy Council purports this optimism by stating a 32% increase in the market of wind energy itself in the year 2006 in spite of supply chain difficulties (GWEC, 2007). Figure 1 shows capabilities of different nations.

With European counterparts making their presence felt in the wind industry, UK seemed to be lagging behind in 2007. However, the rise of wind energy acquisition drive via the 2010 target of 10% electricity generation from renewable by the government saw UK wind industry surpassing Denmark  as reported by BWEA in its 2008 Annual Review. In 2008, UK was reportedly generating 3240MW worth grid connected wind energy (BWEA Annual report, 2008). 1.3. Power from the Wind

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Wind energy ranks second to solar energy in terms of extractable power per year as shown in Table 1. However, even with a high extractable energy value, wind energy is not without its share of  disadvantages like the creation of drag or wind shear, turbulence it creates and most importantly its variability. As of now, the research positively stands capable of overcoming these hurdles and the technological know-how available is more than sufficient for dealing with extraction process. 1.4 Isles of Cumbrae

Regarded as Scotland’s most accessible Island (Cumbrea Tourist Association, 2009). Isles of  Cumbrae (55° 45′ 7.2″ N, 4° 55′ 48″ W) is Island just 10 minutes by ferry to the west of Scotland’s Ayrshire coast. Millport is the only town situated to the south of the Island. The Island itself is 3.9 kilometres (2.4 mi) long by 2 kilometres (1.2 mi) wide, rising to a height of 127 metres (417 ft) above sea level at "The Glaidstone" - a large, naturally occurring rock perched on the highest summit on the island. The population on the Island according to 1991 census is 1434. However, for this report a population of 1830 is being assumed considering a 0.276% population growth (The world fact book, 2009). This report will demonstrate the value of building a wind turbine in the Isle of Cumbrae and show its significant benefits for the environment, and people. This project will also show that the wind turbine is financially feasible. There are four main parts; the first part is dealing about assessments of  the wind speed and choosing the place and calculating the power requirements for the Island. The second part shows the chosen system and subsystem design. The third one is providing the construction and others project plan. Finally, cost and income estimations are considered to find the financial feasibility.

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2. PROJECT OVERVIEW 2.1 Purpose and Scope

Our team has been commissioned with the purpose of reporting the feasibility for a wind turbine on the Isles of Cumbrae. This exercise involves an investigation into a number of technical and non-technical issues which will be dealt with in detail here forth. This feasibility report has been intended with certain aims that the team unanimously agrees upon in order to obtain maximum benefits from the project. Following is a description of these aims:  

Report is intended to keep the interest of the denizens of the Isles of Cumbrae as top priority. Considering the ecological welfare for Isles of Cumbrae, the turbine will have to follow certain standards in quality, environmental protection and health and safety when recommending the feasibility of the project.  The report will undertake a discussion and analysis of the planning, construction, operation and decommissioning stages to establish the economy of the wind turbine while keeping the environmental and ecological protection of the Island and the interests of its people at heart. In order to have a considerably correct measure of decisions and their implications, a set of  assumptions are being considered. These help the team to establish an approximate measure of  feasibility and make it easier to arrive at a logical decision in view of the dearth of literature regarding minute details that need essential consideration. A list of these assumptions is as follows: 



  

All calculations involved are all intended to provide a rough idea of the power obtainable and extractable. The measurements in the actual stages will reveal precise values of the entities being dealt with. The equipments and their specifications are kept as close as they can be to those that will actually be employed in the procurement and construction stages. No such compromise in costs will be considered and a more prudent approach will be taken for almost all costing. Present acceptable standards of environment and health and safety, following as much published guidelines available will be considered. All financial analysis will be kept down to the basics assuming a constancy of inflation. In addition to these explicit assumptions, certain detailed assumptions will be implicitly mentioned wherever they are being made in the report.

All in all, a prudent approach in all aspects involving decision making will be taken in the best interests of the company. 2.2 Report Organisation

In this section, a general idea of what is to follow is given. The structure is kept as simple as possible and is such that the approach to the final decision becomes clear implicitly. The team has followed the flow chart below in arriving at the decision and hence the report is structured accordingly. The project aims were translated into a set of criterion which helped us arrive at the final decision on site of the turbine, primary design analysis including initial calculations dealing with available and procurable energy and costs involved in such a design. The design choice was made 8

considering the cost and benefits of at least three design choices that will be explained further, and the particular reason for the final selection.

This has been followed up by further analysis of the energy calculations. Thereafter, design of  each subsystem suitable and compatible to the calculated energy values in the secondary analysis is done with as much references that could be made to available literature. This particular analysis is supposed to be prudent and is to provide a logical but not accurate idea of how much energy will be produced. Each member on the team has made an analysis in the different aspects of the design system including the current costs sourced from the internet. Each system has been integrated to form the final layout  design of the turbine including the site layout prior to construction phase (that includes transport and logistical specifics and costs) and that which will be included in the  planning permission along with support statement and other related documents. Incorporated in the construction plan will be the quality, environment, health and safety directives and related costs incurred as a result. Thereafter, gross investments will be compared with gross revenue figures obtained from the follow-up or secondary revenue analysis to arrive at the   financial feasibility in light of other important factors effecting feasibility of the wind turbine like   public acceptance, environmental and health and safety impacts etc. A follow-through of the decision will be made in form of recommendations to the board of  directors. The report is intended to be simple in its construct so that its discourse is easily understood by anyone irrespective of knowledge of wind turbines. The annexure contains the analysis and calculations dealt by the team for the report. The decisions made and the difficulties faced during the project are mentioned along with the necessary information for understanding the decisions made.

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3. SITE SELECTION In consideration of site, there are certain essential points that require to be ascertained before any logically supported statement can be made. Out of the most important points that need consideration is the wind statistics at the potential site. However, for any site, much of the metrological data from met stations is of little use in predicting the actual power in the wind (Nelson, V., 2009). Even when certain measurements methods like ‘wind atlas method’ may come handy; these predications cannot obviate on-site measurements that can only happen after approval of the planning permission (Garrad Hassan). A brief description regarding the various site selection considerations follows before the final decision analysis is presented: 3.1. Wind speeds

As mentioned earlier, wind is the fuel for the wind turbine which generates electricity. Its abundance is positive sign but the form (gusts or gales) in which this abundance prevails needs to be essentially known. Wind prediction strategies usually involve wind maps or atlases or sophisticated prediction software like Geographic Information System (GIS) like Digital Elevation Model (DEM) analyses terrains with relevance to wind energy prospecting (Nelson, V., 2009). In the present case regarding the site selection on Isles of Cumbrae, a total of five site locations were selected by inference from the Meteorological office (Met Office, 2010) and using the UK wind speed database (Renewable UK, 2010[2]). A list of all selected locations follows: 1. 2. 3. 4. 5.

N1656 N1657 N1655(denoted 2 in figure 3) NS 1555 (denoted 3 in the figure 3) N1756 (denoted as 4 in the figure 3)

Figure 3: Primary locations based on high wind speeds

Figure 3 shows the choices made with an intention to investigate the locations on the Island that have high average wind speeds. As indicated, location 1 N1656 is the best place as it has high average values of wind speed for different heights. A set of rough calculations for estimation of extractable wind energy at each of the above locations is included in Annex 1. It briefly considers the acceptability of each particular location along with energy values.

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3.2. Noise

According to BWEA, a wind turbine farm at a distance of  350m away generates as much noise as noise from a flowing stream about 50-100 metres away(BWEA, 2009). However, this is not to say that measurements would not be done in the site assessment phase prior to construction as it would be a non compliance of the aims of the project. Figure 4 (Klug, H., 2002) shows the extent of noise in dB that is produced from different power rated turbines. This plot can help in making crucial trade-offs when power vs. noise is being considered as the relation of power and noise arises from the operating conditions and hence, the choice of  a wind turbine’s blade pitch setting and its rotational speed is a compromise between noise radiation and energy production (Klug, (Klug, H., 2002). In other studies from a number number of different countries like Sweden, Netherlands apart from UK, the recommendations that followed were to include cumulative noise impact evaluations within 35-45 Db for high frequency and 10dB for low frequency components in addition to potential shadow flicker and turbine visibility impacts (Minnesota department of health, 2009). The reduction in noise from the turbine is one of the ways of countering the problem. The extent of technological sophistication achieved in insulating the hub and shaping the blades has been of  great aid in assuming the reduction of noise by similar appropriate measures like active noise reduction   for gearboxes (Illgen, A., et al, 2007) and acoustically absorbing tiles usually secured to the walls of  the hub (European patent EP0657647). In the SMART based decision making approach each site has been given a numerical measure to establish its position amongst others. 3.3. Environmental Impact

Impact of wind turbines on the environment in itself spans a number of topics. A verification program undertaken by U.S Department of Energy in association with EPRI discussed a number of  environment related issues like wildlife impacts, and impacts on areas of historical, archaeological and cultural heritage, visual and aesthetic impacts (Green Mountain Project, 1997). Discussion of some relevant issues will now be in order: 3.3.1. Wildlife Impacts: The prediction is that these are limited or not at all. The locations chosen are far away from large animal habitation areas and also away from forests and hence the elimination of need to heavily de-forest will not have an indirect impact on the wildlife on the Island.

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3.3.2. Impacts on Historical, Archaeological and Cultural heritage: In view of avoiding conflicts with historical conservation societies, the sites at N1555 and N1756 are least appropriate on account of a war memorial in the vicinity of the former and the famous Glaidstone near the latter. Similarly, N1656 is located in the Golf course and hence unsuitable. Location N1655 isn’t suitable either as it is too close to the town of Millport that is bound to have adverse affects on the community including, noise and visual impact related health issues. 3.3.3. Visual and Aesthetic impacts: The analysis of these impacts is to some extent subjective and is therefore prone to variable assessments. In order to obtain a better insight, simulation mechanisms exist but face the problem of accurate representation of impacts of significant vertical structures. Colour photomontage and video photomontage are useful techniques and are likely to be used in the pre-planning phase of the project, in spite of both being limited by some problem in representation and public acceptance of results. Nevertheless, these are the extensively used techniques (Thomas, G.W., 1996). 3.3.4. Electromagnetic Introduction: A wind turbine can act as both transmitter and receiver of  electromagnetic interference. Hence, its protection from its own radiation and from other forms that may be rare or limited in locations 1, 2 and 3 but not 4 and 5 must be considered. Critical elements that come under EM influence are the control systems under the hub and nacelle and the best way to protect these devices is by electromagnetic shielding. In order to ascertain the shielding effectiveness required, a sense of EMI strength needs to be calculated. One of the ways in which EMI may be minimised to avoid its effects on communication signals between hub and the base station is by using a GSM transmitter placed at the entrance, inside the cast iron hub. This is following a documented study of  EMI on large wind turbines (Krug, F., et al) This is predicted to be more effective at locations where ambient EMI is minimal and under limits that don’t affect communication signals. si gnals. 3.3.5. Soil Conditions: This impact is one that is effected by and also affects the site selection. A strong foundation is prerequisite of a large turbine intended for generating power to be sufficient for an island the size of Cumbrae. Preliminary research has resulted in selected locations being situated in differently typed soils or ground conditions. The overall quality of soil on the Island is stable with mainly rocky costal platforms. Each location is marked according to its suitability to sustain a weighty turbine and hence extend to its life and performance throughout lifetime (See Annex 2) 3.4. Accessibility

For a project of this magnitude, cost saving becomes a decisive factor during feasibility study. The locations rate differently based on their accessibility at the very first inference such that locations 4 and 1 gain a preferentially favourable rate while location 5 gains the least rated value. The transport and availability of on-site space for a aesthetic and well structured site layout not only impacts the working conditions but also helps in environmental and ecological conservation such that the openness allows environmentally responsive changes that are highly limited by cramped site layouts. The former openness can be achieved at locations 1 and 2 but not at 3, 4 and 5. A numerical rating for each of the above issues is done by assessment for each site location and used in the SMART based decision making. Although a logical conclusion may be arrived at, further detailed pre-assessments are required in the pre-planning phase including a public survey that establishes no objection to eventually selected final location. 12

3.5. SMART Analysis

When using this tool, weighing of parameters actually is prioritising and is intended to be in-line with the aims of the project. It is evident from table 2b, that for the reporting team, environmental issue was most important and was weighed at 34% of  overall importance. Then, the power providing capability through wind speeds was rated second most important at 31% and Accessibility at 19% was followed by Noise impacts at 16%. The weighing is in accordance with standards and reflects the team’s preferences of important issues for the project. So, from the table above it can be seen that location NS 1657 is the best place for building a turbine. The document related to the above analysis can be found in Annex 3. Figure 2 give some primary information of the site selected.

Note: in both the above tables *includes impacts on wildlife, historical, archaeological and cultural heritage, soil; visual and aesthetic impacts; soil conditions and EMI.

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4. TURBINE STRUCTURE SELECTION After the selection of site, a thorough investigation of wind speeds was performed and the variation of wind on a monthly cycle in year was tabulated. This revealed higher speed winds during the winter months and relatively lower speeds in summer months. Based on these wind speeds (UKwind forecasts, 2010), a value of energy for every month was determined which helped in finding the power generation for that month. Table 3 gives average monthly values of wind speeds at N1657. For analysis in this report, these monthly values will be taken as absolute measure of wind speeds and is assumed to provide with approximately correct values. Power in kW and energy production in each month is also listed. In Annex 4, detailed calculations are described for three individual heights at 60m, 80m and 100m. This choice of heights was based on majority of design types having diameters in this range. For each height, two diameters were considered and calculations yielded. In this document, the value of Cp is taken as 0.37 just for the sake of evaluating the maximum (even though unattainable) power and energy values. The efficiencies of generator and gearbox were 80% and 95% respectively. This yielded in overall efficiency of 28%. Each combination of height and diameter gave a different value of power and energy generation for a year. Please note that the recommendations of Annex 4 are without costbenefit trade-offs. The next step was to consider a single design with a particular height at a particular rotor diameter. A number of issues affected the design choice and some of them were:  

Costs to be incurred against income gained Conformation of design with stipulated standards  Power values that should produce energy values that should be optimised against demand on the Island  Access to transmission lines of the National Grid Each of these will give rise to trade-offs that will help in deciding the design that conforms to standards, provides acceptable energy values to cover demand and to save costs by optimising design. 4.1. Cost-Benefit Trade-offs To build a successful wind turbine, the most essential factor is to consider whether the wind turbine is economic or not (Nelson, V., 2009). Because machine cost increasing quicker than energy production, the unit costs of energy production which calculated from energy production divide machine cost shows a slowly rising trend with size increasing (Harrison, R., et al, 2000). 4.2. Design Standards Some of the important guidelines that the company will have to follow are the Grid Codes. The Grid Code covers all material and technical aspects relating to connections to, and the operation and use of, the GB electricity transmission system (Grid Code documents, 2010). Apart from these are the environmental protection standards to be followed during the construction, operation and decommissioning stages. A collection of various codes to be accepted will be enlisted as and when their need arises within different subsystem analysis later in the report. Some general requirements that the design needs to conform to are: 

Energy supply needs to lie within specified limits so as protect the grid from undue failures due to malfunction at the turbine’s end 14

 

The power needs to be supplied at a connection point at 400kV, 275kV or 132kV lines. The equipment at the connection point needs to be supplied by the users (i.e. the company) and needs to follow power quality, level and variation specifications from the National Grid.

4.3. Demand on the Island of Cumbrae Since the aim of the present feasibility study was to provide on the electricity needs of the Island, the demand on it needs to be known. According to sub nationals electricity demand 2009 (Subnational consumption statistics, 2009) the annual domestic energy consumption in the North Ayrshire area is 4MWh/year/person and this value is cannot be assumed to apply to the Isle of Cumbrae because of the fact that it forms a rather small part of North Ayrshire region. Hence, the demand is assumed to be 3.3MWh/year/person to counter the lack of information in published literature. Even then this gives a clear picture of demand in the region. In order to be able to calculate demand, the population on the Island has been estimated to grow from 1434 to 1830 as per the UK population growth rate of 0.276% as estimated by CIA (The world fact book). In this way, the value of demand will be 3.3x1830=6039MWh/year. Isles of Cumbrae do not have any industrial settings and enterprises and majority of its demand for electricity arises for domestic purposes. In order account for the electricity required for sub domestic purposes like electricity for streetlights and basic public amenities, the team proposes a thorough investigation. However, in lieu of absence of any data on this extra demand an assumption that this demand will equal 30 person’s demand is made. Such that number of people on the Island will become 1860 and the demand rise to 6138 MWh. Therefore, the capacity factor stands at 6138: (8760x1.7) =0.412=41.2%. 4.4. Access to transmission lines of the National Grid Under norms of the National Grid code documents, the users (i.e. the company) will be required to make the power available to the grid by means of  their own transmission lines if  necessary. In the present case, the nearest point from the British Grid is 870m away and the path is almost manageable. The point of connection is shown in figure 7. 4.5. Decision Point Based on the above trade-offs, a design that was cost effective, could lend to easy standardisation in compliance with current rules, could satisfy demand on the Island and also was easily connectable at reasonable costs was to be selected by the team. Since a number of factors were being considered, it was easy to lose sight of the aim and so each design was analysed and based on their performance on these parameters, the design with 80m height of tower with 80m diameter of   rotor was zeroed in on. The decision analysis was subjective and was made keeping in mind the fact that the power generated was going to be sourced to the grid with a collateral agreement requiring the demand on the Island to be satisfied with reduced costs or ample benefits. This collateral agreement is 15

then again subject to a number of variables but this is what the team has proposed to forge easiness of  obtaining the permission to construct in case the turbine is built anyway. Turbine design that has eventually been chosen is a horizontal axis, up wind and pitch controlled type of wind turbine. Figure 8 shows a very basic schematic of the chosen design. The team intends to review the performance of this design in pre-planning and measurement stages before actual construction when more values for calculation and more information will be available. However, it is predicted that many changes are unlikely to occur and the design will only be reviewed and minimally modified.

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5. TURBINE SYSTEM DESIGN Until now in the project, the decisions on where to build the turbine and what design of turbine to build were were investigated and presented. The subsequent sections to follow hereafter will contain preliminary information on the turbine’s subsystems each discussed by correspondingly relevant members of the team. Following is the list of the subsystems that will be further discussed:      

Aerodynamic subsystem Mechanical subsystem Electrical subsystem Control subsystem Foundation subsystem Tower Layout

5.1.

AERODYNAMIC SYSTEM

The following has been studied under the aerodynamic system of the turbine for deciding the location, design and also the design of rotor essentially used for conversion of wind energy into rotational energy of the rotor and thereafter mechanical energy of the shaft. 5.1.1. Wind Rose and Wind Distribution To determine the exact design of the wind turbine and choose the location, the particular wind condition in Cumbrae Island should be considered firstly. From this point, the wind rose data from the nearest wind station and annual wind speed distribution could be helpful. The wind rose data in Prestwick, which wind station, is quite near Cumbrae, between 1996 and 2005 shows that the majority wind in Western Scotland came from Southwest. And the wind speed between 11knots (5.66m/s) and 27knots (13.9m/s) could be seen as the most normal wind speed in this area. Meanwhile, depending on the average wind speed (7.8m/s) in Cumbrae at 45 meter (Energy statistics: wind speeds 2010), the wind speed at different height could been converted with the formula 2 3 Power=0.5xetaxPixradius xaverage velocity xrho Then referring to average wind speed (8.2m/s) and wind distribution for every month in Western Scotland (Energy statistics: wind speeds, 2010), the wind speed for every month in Cumbrae at 80 meters high has been draw as follow and wind rose has been cited as well.

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From the figure above it could been seen that the lowest wind speed occurred in July and August which was accounted for 5.9 m/s, while the highest wind speed occurred in January which was accounted for 10.7 m/s. Overall, from the data above it could be concluded that the annual wind speed in Western Scotland is between 5.66m/s to 13.9m/s and the direction is from southwest. However, more accurate data shows that the rated speed could only reach into 10.7m/s, so the turbine rate power generation should relate to wind speed at 10.7m/s. 5.1.2. Rotor Design

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Considering the wind turbine diameter (80m) and rated wind speed (10.7m/s), 5 types of wind turbine rotor was chosen from the top ten large wind turbine manufacture. Meanwhile, the location of  the company was considered as well in order to reduce the transport cost. The detail information was constructed in the following table 3. Please refer the cost assessment in Annex 9. Taking into aspects like available data, suitability to wind speeds and costs, in conclusion, V82 wind turbine rotor which is manufactured by Vestas is chosen. 5.2.

MECHANICAL SUBSYSTEM

Under this subsystem, an investigation of the yaw and pitch mechanisms are discussed. It gives a general overview of how these mechanisms work and how the team intends to approach them. 5.2.1. YAW SYSTEM The yaw arrangement of wind turbines is the element responsible for the directing of the wind turbine rotor face into the wind as the wind direction changes. 5.2.1.1.

Yaw bearing

One of the key mechanism of the yaw system is the yaw bearing. It is made up of either roller or gliding type and it acts moveable connection between the tower and the nacelle of the wind turbine. The yaw bearing is done to withstand high loads, excluding the weight of the nacelle and rotor, comprise the kinetic energy of the wind. It is mostly made up of hard stainless steel. The thickness is dependent on the weight of the nacelle and the forces of wind.

5.2.1.2.

Yaw drives

The yaw drives is a means of rotating of the wind turbine nacelle. Each yaw drive comprises of powerful electric motor and a great gearbox, which enhances the torque. This is used to drive the nacelle. The yaw drive diagram above is made up of three parts

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•

The mechanical pump (Bonfiglioli, 2009) which is located at the top. It is used to generate Figure 12: Pump system for yaw gears the rotation which is required to cause the movement of  the gear teeth. We can use the calculation below to calculate the torque and mechanical power. Torque is defined as T= r x F

is the torque vector r is the displacement vector =0.2m (assumed) F is the force = mass x acceleration Τ

Mass = 125 000 kg (estimated mass of the nacelle) Acceleration= 9.81m/s T= 0.2 x (125000 x 9.81) T= 245250 Nm Power (KW) = torque x 2П x rotational speed Rotational speed = 8m/s (assure due to the fact the it will have to be monitored so that the nacelle will be position properly) Power (KW) = 245250 x 2 x 3.142 x 8 Power = 12329.208 KW Power =16527HP This is use to calculate the power required to turn the nacelle round and it is the mechanical power of the motor. The motor is four in number so the power calculated is divided into four and the reason is that is to reduce the stress load on the motor. It is also designed in such a way that three of the four motor will be able to turn the nacelle and the one left is use for safety reason in case of damage to any of the drive or increase in speed of the wind. •

Gearbox system is also part of the yaw drive. The gear system is used to reduce the amount of mechanical power to be applied. Power on one of the motor = 16527/4 = 4132HP

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So to reduce the mechanical pump capacity we can say that we need a pump of about 40-45 HP The mechanical power varies but the lager the power the smaller the gear box. •

Gear teeth: the gear teeth are attached to the yaw bearing teeth which has to fit with the teeth. It is most made up of hard steel to make it hard enough to carry the weight.

Figure 13: Yaw system mechanism 5.2.2. PITCH SYSTEM The pitch system is similar to the yaw system only with a smaller radius n taking in considerations the weight and diameter of the blades. 5.2.2.1. Pitch Control •

•

• • • •

Working way electromotor pitch adjust, independently blades adjust Pitch –controlled 4-points double row angular contact ball slewing ring with inner ring gear bearing Pitch adjusted rate 7.5 /s-12.5 /s Pitch adjusted angle range -94 Battery lead acid, 250-300VDC Slip ring 29 rows

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5.2.3. OPERATING CONDITIONS AND BEARING DIMENSIONS 5.2.3.1. Bearing Loading The yaw bearing is mounted in a tubular tower is required to endure for 20 years considering 50% operating time so considering a bearing of this capacity. Also take into consideration that the wind turbine might be turned once or twice a month. The tables above shows the bearing size and an experiment carried out. If the same bearing is to be used we will consider condition 1-5 when determining the bearing limited load. 5.2.3.2. Brake system The mechanical brakes are applied as a support system for the aerodynamic braking system, and as a stopping brake, once the turbine is stopped in the case of a halt controlling the turbine. The disk brake involves a flat spherical brake disk and plurality of brake callipers with hydraulic pistons and brake pads (Gasch, R., Twele, J., 1993). The hydraulic brakes (pump, valves, and pistons) are able to fix the shaft and nacelle in a fixed position .The highest speed of the rotating shaft is used to calculate the force that the blade needs to apply. The drum brake will have the same diameter as the low speed shaft while the disc brake will have the same diameter of  the high speed shaft. Parts of a brake system are Conveyors, flywheel brakes, mining vehicle brakes, railroad maintenance equipment, tension brakes. Since we have a generator with a maximum revolution of 1500rpm from the graph above we will apply a mechanical pressure of 5HP to hold the shaft in to position at the high speed region. Using the graph we can also calculate the pressure to be applied on the brakes on the low speed shaft, yaw bearing and pitch bearing. This can be done be using the revolution at which the gears are rotation and applying the force required.

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5.2.4. GEARBOX FOR WIND TURBINES A wind turbine is a machine that translates the kinetic energy in wind into mechanical energy. Wind turbines utilize a gearbox (Gears and Gearbox, 2010 ),   jointly with a generator to convert mechanical power into electricity. A range of gears and gearboxes are employed in wind turbines for connecting low-speed shaft to the high-speed shaft and increasing the rotational speeds. These gearboxes increase the RPM in the wind turbines to a level that is required to produce electricity (Eaton Corporation, 1997 ). Figure 17: Mechanical Pressure vs. RPM standards 5.2.4.1. • • •

TYPES OF GEARBOX USED

Planetary Gearbox Helical Gearbox Worm Gearbox

Planetary gearboxes are mostly used in modern turbines because of the following reasons. 5.2.4.2.

ADVANTAGES OF USING A PLANETARY GEARBOX

This gearbox offers many advantages as compared to other types of gearbox. Some of them are: • • • • • • • • • • • • •

The gearbox drive increases the efficiency and provides extremely low speeds. These gearboxes deliver high reduction ratios and transmit a higher torque. These gearboxes are compact and lightweight, requiring little installation space High reliability due to proper distribution of stress among different load-bearing components. Higher torque to weight ratio Low backlash Compact size Less weight High cyclic and radial load carrying capacity Improved efficiency Modular construction allowing assembly in several stages Greater resistance to shock  Improved lubrication

Planetary gear Planetary gear is an outer gear that revolves around a central sun gear. Planetary gears can produce different gear ratios depending on which gear is used as the input, which one is used as the output 23

5.2.4.3.

MATERIALS USED

Materials used for constructing them including: • • • •

Stainless steel Hardened steel Cast iron Aluminium 5.2.4.4.

GEARBOX SPECIFICATIONS

There are a number of performance specifications which must be considered while choosing a gearbox for different industrial applications. Some of the important specifications (Leech, 2009) are: 1. Gear ratio: The ratio may be specified as x : 1, where x is an integer. The circular speed v {m/s} = 2π r n Where r is the radius {m} n is the revolution per second {RPS) n = v / 2π r To convert RPS in to RPM, multiply RPS by 60.

Therefore, Gear ratio: 52:1

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