Design of a small Hydro-power plant.....pdf

20 1 5 Designing a Small Hydro Power Plant Capable Of Producing 10 MW of Electricity at Webuye along River Nzoia Final Year Project University of Nairobi 14/4/2015 Declaration This work and material produced in this report is our original work and it has not been presented or published elsewhere for academic purposes. Chol Dhieu Gabriel F18/34749/2010 Signed……………………………………………………………. Paul Odhiambo F18/29902/2009 Signed…………………………………………………………… John Odhach F18/29942/2009 Signed……………………………………………………………… I Dedication We dedicate this project to our Almighty God who has been supporting us throughout the duration of the project. We have also dedicated this work to our parent and sponsors. II for his support. friends and sponsors for their tireless support throughout our studies at the university. In addition to this. Prof. Mutai who drove us from Nairobi all the way to Webuye and also the many short trips within Webuye safely. He was invaluable when we were conducting site evaluation. We would like to give our gratitude to Mr. we would also like to appreciate the Kenya Power staff at Webuye for providing us with the power consumption data for the area and reliable future demand trends of the area. Munyasi for his wise guidance. Sayi of KTDA who provided us with a lot of information and reference material on the planning.Ogola. We would also like to thank Eng. He has been very supportive and essential in us achieving our objectives. This data was very essential for the professional work that we conducted. We would also like to give appreciation to Nzoia Water services Company (NZOWASCO) for their invaluable advice regarding the River Nzoia. We would also like to thank the Regional manager of WARMA and their entire staff for giving us volumes of data on the River Nzoia. lecturers. design and guidelines on small hydropower power plants. We owe our success in this project to all the above mentioned people. Last but not the least.Acknowledgement We want to thank God almighty for His guidance and protection throughout this project. We also want to thank Prof. We appreciate Eng. III . we would like to thanks the staff of the CDF offices in the constituency of Webuye for designating one of their staff to guide us around the river. We also want to appreciate our able supervisor Eng. Also. Oduori for his support and his introducing us to Eng. Aduol for their constant support especially in facilitating our transportation to Webuye. relatives. He was also gracious enough to accompany us to Kakamega to the regional WRMA headquarters. Ndulu and Eng. Sayi even went as far as helping us locate hydrologist who came up with a practical flow duration curve. We would also like to thank our chairman. Eng. Sayi of KTDA power. In addition to them. He coordinated with the university’s transport department to facilitate our travel to Webuye East County. we would like to thanks our parents. the station location has to be selected as well as parameters like head and discharge from the river has to be determined before any design analysis starts. The entire Bungoma County is suffering from power shortage. In addition to this. In the data collection we used a hand held global positioning and ranging system (GPRS) to determine the gross head by taking some points upstream and downstream and getting the differences as our gross head. we had to visit Water Resource and management Authority (WRMA) at their regional office in Kakamega to obtain the data pertaining river Nzoia and more particularly the point around Nabuyole falls. These industries have been suffering from regular power outages and high cost of grid electricity. Thus. The head losses were subtracted from the gross head to get the net head that was used to calculate the power output from generator or the power to be injected to the grid. Current flow data is not sufficient the design of small hydropower plant. To achieve a good design.5 M) and design discharge are the two most important parameters used for design analysis and selection of hydropower components. the additional power from the hydropower plant will attract investors to the area. Our skills as Mechanical engineering were out of place in the flow data analysis hence we needed to consultant a Hydrologist who later came up with FDC. the net head (Hn= 54. On the other hand the flow rate was obtained from a flow duration curve (FDC). we calculated the head losses due to bends and friction in penstock which affect the final power output. This is because the power from the national grid is not sufficient to cater for the demand of the area. IV . Their responses and readiness to give up their ancestral land especially those living around the river. At the same time in analysis. We carried out research by using questionnaires to get feedback from the local around the site regarding the project. From the analyzed data (plotted FDC) we selected our design discharge to be Q = 21 m3/s which was used for all our calculations. The hydropower plant will have an immediate effect on the industries already set up. They were very friendly and they gave us a lot of information regarding the River and the ownership of land and their thoughts on the project if at all it is going to be implemented. motive us to proceed with the project.Abstract The objective of this project is to come up with the design of small hydropower plant capable of generating 10 MW at river Nzoia passing through Webuye East constituency. Therefore. The estimated cost for this project is KSHS 212. settling basin. the selection of electromechanical equipment i. The design analysis was done based on the economic viability and the site configuration.000. The cost also depend on other economic factors e. The next step was the design of civil structures e. control system was critical. power house foundation and power house building. the Dollar exchange rate affects the price of hydropower components thus make the cost of project to go up or down. speed increaser. Though hydropower is a renewable. There is another environmental concern which is going to affect people living around the plant i.e. weir. The summary of dimensions and quantity of the hydropower components are tabulated under summary section. This needs to be strictly controlled in order to reduce noise pollution to aquatics and people living around the site during construction and operations V . This is because it is the critical determining factor in the planning of small hydropower plant. in the case of this project.e.00. In addition to this. The selection of this turbine was based on specific speed. The other important section was the cost of project. the exact cost of this project can be determined during the implementation though large deviations from the estimate are unlikely. power output and discharge from river. green energy source it has some draw back which can be analyzed for sake of animal life in the river and around the river. headrace.g. This project can be funded by private organizations. Therefore. The Francis turbine selected using the selection criteria discussed in chapter 2 of electro mechanical equipment. intake. The dimensions were calculated using net head and design discharge discussed above. head-tank (fore-bay). The dimensions of the civil structures and electromechanical equipment were calculated using empirical formulae and other formulae from reference materials.g. generator. penstock. the sound levels from the power house are at times very high. we got the cost estimate of civil structures and their work and the estimate cost electromechanical equipment in the market. turbine. net head. Hence. This is because most of the components are imported into the country from specialized manufacturers. banks and the government Return on investment is very high since this plant is most likely to generate revenue in the millions of shillings per day if the surplus electrical energy is channeled into the national grid at the feed in tariff (FIT) rates. The generator type selected for this design was the synchronous type and the rest of specifications of generator are in the conclusion part.524. There are tables and charts used for the selection of Francis turbine above other turbine types which is discussed in the literature review. rotational speed. Therefore. However. we recommended that the other specialist in other fields to be involved. the project is capable of producing more than 10 MW of electrical energy. we recommended the implementation of this Project for it will greatly benefit the Webuye residents’. Therefore. during the implementation of the project. If this project is implemented then the community and country at large can benefit. Lastly. industries and the country as a whole in meeting the desired electrical energy output. This project will create employment for the locals and skilled Kenyans’. pursuing this will be out of our small hydropower bracket. VI . in conclusion. Net head (m) HG Gross Head (m) I. Constant k. Rotational speed rpm p. depth of water in channel (m) HN. Diameter m D. Absolute velocity (m / s) d. Power W Q. conduction factor L. Height of shroud C. Reynolds number V. Width of channel (m) b. Acceleration of gravity (m/s2) H. Force N g. Area (m2) B. Flow rate (m3 /s) r Radius m Re. Specific hydraulic energy (J/kg) F. Difference between inlet and outlet radius of runner (m) A. Pressure Pa P.Notation Nomenclature a. Length m m. Second area moment of inertia (m4) K. velocity (m / s) U Peripheral velocity (m/s) W Relative velocity (m/s) VII . Diameter m E. Mass (kg) N Number of measurements m n. Z Number of items m WRMA: Water resource management authority FDC: Flow duration curve BEP: Best efficiency point FIT: Feed in Tariff VIII . .......5...........4 Advantages of a Small Hydro Power Plant: ................................................ 7 2..................................5........................................................................................................................................6.......4..... 2 CHAPTER 2...................3 Transient flow .......IV CHAPTER 1.................................................................................................. 7 2.............3 Stream Flow Characteristics .................... 2 1................................................................Table of Contents DECLARATION ...............................................................2.. 1 1...5....................................................... 6 2...........1 Run-of-river schemes .................1 Head losses due to friction ..... II ABSTRACT ....4............ 8 2......................................................6...6 Penstock .............. 4 2..................1 Introduction ... 3 2.................................................1 Location of Intake ...2.....................................................................5..................................4....................... 8 2.............................2..................................................6 Loss of head through valves ...2 Side intake.......................... 5 2................................................................. 7 2...........................5 Disadvantages of a Small Hydro Power Plant .............................. 5 2............7 Tailrace .................1 Spillway at the head-tank .............................................................................................................................................................................6........3 Settling Basin .............................2........................................................................ 3 2..............1 Introduction .........................5................... 6 2.................................................5............4..................... 6 2................................ 8 2...............5...................................................5.................. 5 2..............7 SITE EVALUATION METHODOLOGIES ......................................................................................................... 1 1........ 5 2............ I DEDICATION .................................. 7 2..........................................1 Intake Weir..4 Headrace (channel) ..................3 Reasons for the Project ..........5 Head tank (fore-bay) ................................2 Objective of Project ....................................................1 Introduction ............................................................ 7 2..................... 4 2..0 INTRODUCTION .................4 Fundamentals of hydraulic engineering .............................4..........................2..............1 Penstock Material................................ 3 2......................6 Project Area ...............................6.................................................. 4 2................ 8 2........................................................................6.............................2.........................6................................1 Schemes can also be defined as:........5 Loss of head in bends ................................................................................. 4 2.........................2 Stream flow records ...........................................................................................................................4 Flow Duration Curves (FDC) ..................................5.............................6 EVALUATING STREAMFLOW ..2...........................................................................5 Evaluation of gross head ...............0: LITERATURE REVIEW ...5............................................................................................................................................................................................................. 7 2........................................4......... 1 1................. 1 1.6.................................................................................... 3 2.................................................. 8 2............................................................ 7 2....3 Trash rack (or screen) losses .......1 Definition and classification of small hydropower .....................................................4.....................................................4...........................................2 Loss of head due to turbulence ........... 1 1............................................... 4 2.............1.................5........... 7 2......................5 HYDRAULIC STRUCTURES (CIVIL STRUCTURES) ................... 3 2.6 Estimation of net head ...................4 Loss of head by sudden contraction or expansion .....2 Site Configurations .................................... 8 IX ...........................2...................................... 4 2.................. 7 2..2..............................................................................................................6.......................................................................................................................... ............................4....................................1 Net head .1 Powerhouse ................... 14 2............................... 17 3.......................................8................ 24 3... 13 2..................................................................................................... 19 3.................................9...............2 Rotational speed. 10 2...........................5..................................................9.......... 9 2.................. 12 2....................................1 Type of Generator .8................................................8............................................1 Determination of power output ........................................8...... 16 2.....................................................9.........................................2 Trash-rack material ..............................9.....................................1 Types and configuration ........7...........................................................................8.........................................................9....................................4..................................................................................... 5 Biological impacts ............................. N ......... 9 2.........................1 Inlet diameter Di......................................... 16 2.2 Exciters ................................... 16 3..8.............................................................8.....9...........................2 DC control power supply ...2 Landscape impact........1 Design of electromechanical equipment ............................................. 23 3........5 Runaway speed ........................... 23 Knowing the specific speed..2 Impacts in the construction phase ......8.........7.......................3 Specific speed ... NS .. .8........................... the required NPSH can be calculated as............... ELECTROMECHANICAL EQUIPMENT ................. 17 3............................... 11 2..................6..... 12 2...8...9......................................3............... 12 2.............................1.......................................................1 In the reservoir ........................................................4 Turbine selection criteria ....4 Switchgear equipment .............2 Discharge .. 9 2...............................1 Specific speed....8....................9........ 2.........8...................8............................................. 11 2............................................ 18 3....... 15 2................8........................... 10 2...................................8.............................................................8......3 Dimensions of Francis turbine ........................................................................8............6................................................................................ open canals.. 14 2................................................2.............................8.....................2 Design of Francis turbines ... 12 2............... 11 2........................................................... tailraces...................7........4...................................................9 ENVIRONMENTAL IMPACT AND ITS MITIGATION .......................................................................................................................9.................2 Health impact ..................9.....1 Burdens and impacts identification ..7 Generators ........................................................2..6 Turbine efficiency ................................2...........................................8 Automatic control .....................2.....5......................................7.................................................................4 Impacts arising from the operation of the scheme ......... 14 2.........................................................................6 Impacts from transmission lines ........... 15 2.........1 Visual impact ......8..7.....8................................................................................... 9 2............................ penstocks..........................................3 Cavitation ...........4 Rotational speed .............. 16 2.................... 16 2................................................2..........................................................8........................ 15 2..........................1 Introduction ....... 8 2.........................................................................4..........9................1 Sonic impacts ........7 Speed increasers ............................................................ 14 2........8..................................................................2 Hydraulic turbines .........4...1 Plant service transformer ........3 Speed Governors .4.................... 14 2................3 Water intakes........6..................................9.................................................... 13 2... 15 2...............4 Cavitation design .....................8........ 12 2... 20 3....8............................3 Design analysis of the draft tube ......3 Headwater and tail-water recorders ................................................. 13 2........................................................................................ 24 X ............ 16 2........ 19 3.....8............. 12 2...................................... 13 2................. 11 2.................. ............3 Head loss due to friction.............1........................................................ 26 3....8 Head tank .... 3. 36 4................................... hb ......................................................7 Penstock pipes ........2 INDIRECT COST OF CONTRACTOR ................... 36 4..........................................................7.............. 37 4...............3....... 39 5...........7........12 Transmission line ..........8 Canal ...4 Generator Design ...........................3 Administration ............................5 Spillway .......................................................................................................................2 Speed of generator ...........................................................................2...........9 Power house ............... 27 3........................................................1.........................4Generator type ................................3 Head loss in the penstock .................................................1....................................6 Side intake.......................................................... 37 4.............. 37 4..............................1.. 37 4..... .......................7.......... 29 3........... 28 3................................................................................... 31 3.....1 Speed governor .............3 Tail race water level.........................7..........................................................7............................................6 Control facility of the turbine and generator..............................................1................................................... 38 CHAPTER 5........ 26 3.............................................................. 36 4.......................................1.............2 Exit diameter of draft tube............ 38 4....................... 35 CHAPTER 4: PROJECT COST ESTIMATION ......... 31 3....1 Head loss due to entry and exit..........1............... 38 4..............1.....................7.................................7.......................1........................ 31 3.................6...........................................................1 DIRECT COST ......1......................................................................................... 33 3................................................................................................. 34 3................................................................................................................................................................................................... CONCLUSIONS AND RECOMMENDATIONS .........................................................0: DISCUSSION..................4........10 Francis turbine ....................... 38 4..... 37 4...................................................................... 31 3...3.................3 Exciter of generator.....................7................1 Number of poles ......................................... 36 4..........................................1 DISCUSSION .... 36 4.................................7 Settling basin design ........ 28 3.................................4 Fore-bay ................................................................................................................... hV ...........................................................................................................3........................ 26 3....1.....................2 Determination of the penstock thickness.......1 Head tank capacity ........................................ 33 3.............................................. 36 4......................1 Weir height calculations .....1 Engineering cost.............7......................7 DESIGN OF CIVIL STRUCTURES.........................................................................5 Power transmission facility (speed increaser)................................................................................................................................ 29 3.................. 28 3.........................7..7. 36 4...............................................................................................................................................4.........13 Construction supervision .........................................7..... T .......................3 Settling basin ................2 Contingencies ........ 28 3.........................................................................1......................................................................................................................2 Head loss due to bend..... 29 3......................................................................................................11 Synchronous generator.............................................................................................4..........................................................................................5Generator output .. 38 4....... 36 4. 36 4..........................................................2 Intake weir .........3..................................................2.................. tp .....................................................4........5 Intake Weir (Dam) .......... 27 3...........................7......................... 33 3...................... 27 3............2...........1 Preliminaries (for civil structure work).....................3...... 39 XI ................................................. 25 3......8............6 Penstock civil work .....................5.................................... hf .......4 Design of head race (open channel) ...........................................4...... 34 3......................1........1 Penstock hydraulic calculations ......... 32 3................................... .................................................................. Photos of Nabuyole Falls ................................................................ 47 Flow duration curve .................................................... 43 5.. Moody Chart ............... 18 XII .............................................................................................................10: Typical efficiencies of small turbines ...........................6: Range of heads ..................................................................................3 CONCLUSION ................................................................................ 5........................................................................................................................................................ 44 REFERENCES: ...................... Satellite image of webuye ..................................................... 18 Table 2..........................................................................4 RECOMMENDATIONS .......... 45 APPENDICES ................ List of tables Table 2................................................................................................................................................................................................................................................................... 3. ii. 1 . civil works. such as head. Its mature technology and small investment risk. Its low operating costs. The obvious social benefit to a developing local economy and improvements in the material and spiritual life of local residents. easy maintenance and reliable power supply. The desire to harness the existing hydro potential in remote areas of our country. Its suitability for decentralized development. with some positive impact on the environment. This involves the selection of the most efficient and economical turbines as well as an optimum selection of other plant components (e. SHP is the scheme with installed capacity up to 10 MW 1. SHP capacity may vary at different times and in different countries but it has no strict definition. Little environmental impact during construction. SHP stations are classified in terms of their capacity. The need to hasten the pace of rural electrification programs by providing additional electrical energy.Putting into consideration the environmental impact and its mitigation and economic analysis 1. 1. iii. 2.2 Objective of Project To design a small hydro power plant capable of producing 10 MW of electricity under a water head of 57 m along River Nzoia in Bungoma County. water resource potential and electromechanical equipment). v.1 Definition and classification of small hydropower Small hydro power (SHP) may be classified according to different criteria. powerhouse layout and installed capacity of SHP. Generally.0 INTRODUCTION 1.CHAPTER 1. iv.3 Reasons for the Project Before picking on this project we were motivated by the following factors: 1.g.4 Advantages of a Small Hydro Power Plant: i. The need to provide a clean and cheap source of energy for the rural areas to supplement the expensive fossil fuel sources of energy currently in use. fully using local materials and appropriate technology with the participation of the local people. The Latitude is 0.6 Project Area Webuye is an industrial town in Bungoma East District. ii.6166667°. Developing tourism in rural areas. Statistics Webuye has a tropical climate. as well as a number of heavy-chemical and sugar manufacturers. Naming In the pre-independence times. Longitude 34. the largest paper factory in the region. and the land around it is used mainly for subsistence agriculture. vi. Milo.Elevation = 1523m 2 . it is bound to interfere with the river flow and ecosystem. Maraka and Misikhu. Bungoma county in the Western Province of Kenya. vii. after the first white man to visit the nearby Nabuyole falls on River Nzoia. average annual Temperature of 24°C / 75. Villages near Webuye include Lugulu. The area around the town is inhabited by both the Bukusu and the Tachoni. Webuye was known as Broderick Falls.Nabuyole.7666667°. Because its installation involves some site work. Creating more jobs and reducing the migration of rural people into cities. viii. Located on the main road to Uganda.2°F. 1. Relatively high initial capital cost which might make it expensive for individual institutions to afford.5 Disadvantages of a Small Hydro Power Plant i. Must be sited where there is a water fall for example Nabuyole falls which in most cases is accompanied by poor accessibility.[1] Railways The town is located on the main railway from Mombasa to Uganda. iii. This may lead to objection by the local people who might be affected by such interferences. who used to repair shoes for railway workers. Webuye municipality covers 69 square kilometers. Increasing revenue for the local government and income for local people. Webuye is home to Broderick Falls of the river Nzoia. 1. the town is home to the Pan African Paper Mills. Itwaslater renamed after a cobbler. 1 Schemes can also be defined as:- 2. stream flow.3 Planning a small hydropower scheme at river Nzoia The most important parameters in planning small hydropower plant are design flow rate and the net head. where the powerhouse is located. It is going to provide review of site configuration. River Nzoia has water fall which give us the head available for production of electricity.30 m These ranges are not rigid but are merely means of categorizing sites.0: LITERATURE REVIEW 2.CHAPTER 2.2. fore bay and finally to penstock. civil structures and design. electromechanical selection and environmental impact and mitigation. This chapter is very important because it give technical background of the design used in this project. The power output from the scheme is proportional to the flow and to the head.2 Site Configurations The objective of a hydropower scheme is to convert the potential energy of a mass of water.1.2. generation ceases. The two parameters determine the power to be produced and the success of the project. 2.100 m  Low head: 2 . all the data pertaining to the river Nzoia were provided 3 . into electric energy at the lower end of the scheme. Hence. flowing in a stream with a certain fall to the turbine. settling basin. the scheme is run-of-scheme with weir built across the river to divert water to intake. site evaluation.1 Introduction This chapter is going to give the over view of small hydropower and its components. The river Nzoia has enough water and it has water fall. For this design. channel. The river itself is gauged by water resource and management authority. When the river dries up and the flow falls below some predetermined amount or the minimum technical flow for the turbine. 2. Schemes are generally classified according to the “Head”:-  High head: 100-m and above  Medium head: 30 . 2.1 Run-of-river schemes Run-of-river schemes are where the turbine generates electricity as and when the water is available and provided by the river. and to the Roman Empire’s builders of the aqueducts. China. The flow of water through the rack also gives rise to a head loss. The loss was related to length of penstock. sudden contraction and enlargements of pipes. valves and other accessories experiences. 2.4. 4 .4. bends.1 Head losses due to friction The head loss due to friction was calculated in penstock.4.2. Based on the large amount of accumulated experience.by WRMA and from the data we got design flow rate. 2. in addition to the friction loss. when a massive irrigation system.3 Trash rack (or screen) losses A screen or grill is always required at the entrance of a pressure pipe. with entrances. Though usually small. The detailed of design are dealt with under chapter three. racks. The other part of planning was Environmental impact assessment and mitigation measures and Economic evaluation of the project and financing potential. and probably never will. certainly there are particular solutions to specific problems. We used handheld global positioning system (GPS) to get gross head (57m) and coordinates of location of intake and the power house.4 Loss of head by sudden contraction or expansion When the pipe has a sudden contraction there is a loss of head due to the increase in velocity of the water flow and to the turbulence. a loss due to the inner viscosity. was built in Sichuan. 2.2. although many empirical relationships are applied to achieve practical engineering solutions.4. Losses in penstock reduced the power output. friction factor and velocity as the main parameter.2.2 Loss of head due to turbulence Water flowing through a pipe system. a general methodology for the mathematical analysis of the movement of fluids.4 Fundamentals of hydraulic engineering 2. Until now there does not exist. Experience that goes back as far as 2500 years ago.4.1 Introduction Hydraulic engineering is based on the principles of fluid mechanics. that is still operative.2. the planning went ahead to select the plant components with their dimensions and other specifications. This loss also depends of the velocity and is expressed by an experimental coefficient K multiplying the kinetic energy v2/2g. 2. 2. After having all those data in place. This pressure unbalance causes a secondary current. the sudden change in the water velocity can cause dangerous high and low pressures. As for this project such losses were considered. Flow regulation is assigned to the distributor vanes or to the needle valves of the turbine. This pressure wave is known as water hammer and its effects can be dramatic: the penstock can burst from overpressure or collapse if the pressures are reduced below ambient. open or close the gates too rapidly.2. The head loss produced in these circumstances depends on the radius of the bend and on the diameter of the pipe.5 HYDRAULIC STRUCTURES (CIVIL STRUCTURES) A hydropower development includes a number of structures.5 Loss of head in bends Pipe flow in a bend experiences an increase in pressure along the outer wall. the design of which will depend on the type of scheme.6 Loss of head through valves Valves or gates are used in small hydro scheme to isolate a component from the rest. local conditions. or the governor system.4. and a decrease of pressure along the inner wall.4. for instance when the plant operator.  Water conveyance system 5 . where discharge is assumed to remain constant with time. The loss of head produced by the water flowing through an open valve depends on the type and manufacture of the valve. The following structures are common in a hydro scheme:  Diversion structure  Dam or Weir  Spillway  Energy dissipation arrangement  Fish pass  Residual flow arrangement.2. 2. 2. Such losses were calculated and subtracted from gross head. so they are either entirely closed or entirely open. 2. access to construction material and also local building traditions in the region.2. the operating pressure at any point along a penstock is equivalent to the head of water above that point. If a sudden change of flow occurs.3 Transient flow In steady flows.4. For purpose of this project wet masonry dam was adapted. The full design is undertaken under design analysis. 6 .5.5.  Intake  Canal/channel  Tunnels  Penstock  Power house Design aspects and common solutions for these structures are presented below: 2.1 Location of Intake The location of the intake is selected considering the following conditions: Extreme care must be taken in this selection for the development of small-scale hydropower as the cost of the intake facilities significantly determines the development project economy.1 Intake Weir The diversion weir or intake weir is a barrier built across the river used to divert water through an opening in the riverside (the ‘Intake’ opening) into a settling basin.2. Sufficient consideration should. the height of the weir depends on the river slope. (2) Stability of Hillside Slope The presence of a landslide or unsteady slope near an intake weir site causes concerns for possible obstruction at the water intake by sediments from the landslide or erosion. therefore.2 Side intake The side intake is used to draw water from the river to the conveyance hence it is the type of intake chosen for this design due to its simplicity.5. 2. 2. (1) River Channel Alignment For run-of-river types of hydropower plant. Therefore. be given to the stability of nearby hillsides as part of the intake location selection process. the appropriate section within the river channel to construct the intake structure is where the channel is as straight as possible in order to ensure steady and smooth flow of water to the intake and also to prevent scouring of the river banks downstream of the intake site. 6 EVALUATING STREAMFLOW 2.5.5. 2.5.5. It may be built at the intake or at the fore-bay (head tank). The details design of the same is cover in chapter three of this project. the spillway will be installed at the head-tank in order to release excess water and discharged it to the river safely when the turbine stopped it.7 Tailrace It is the conveyance that return the water back in to the river after passing through the turbine.1 Penstock Material The pipe materials chosen for this project is commercial steel for the penstock due to its strength to withstand the harsh conditions.5. 2. Hence. rectangular type of headrace was adapted with masonry type.5. 2.6. 2.6.1 Introduction 7 .1 Spillway at the head-tank Generally. For the purpose of this design it is built at the intake It must have a structure that is capable of settling and removing sediment with a minimum size that could have an adverse effect on the turbine and also have a spillway to prevent inflow of excess water into the headrace. provides submergence of penstock inlet and accommodation of trash rack and overflow/spillway arrangement.4 Headrace (channel) Headrace is channel leading water to a fore-bay or turbine.5 Head tank (fore-bay) Pond at the top of a penstock or pipeline. 2.3 Settling Basin The settling basin is used to trap sand or suspended silt from the water before entering the penstock.2.6 Penstock A penstock is a close conduit or pressure pipe for supplying water under pressure to a turbine from fore-bay or head-tank. 2.5. The headrace follows the contour of the hillside so as to preserve the elevation of the diverted water. 2.5. serves as final settling basin. 6.6.4 Flow Duration Curves (FDC) Way of organizing discharge data is by plotting flow duration curve (FDC). The plotted curved is put at the appendix. Also the topographic conditions of the site must allow for the gradual descent of the river in a river stretch be concentrated to one point giving sufficient head for power generation. An FDC shows for a particular point on a river. stream flow records can be obtained from Water Resource and Management Authority (WRMA). The net head was obtained after subtracting those losses. intake. bends and valves.6. from trash racks.6. 2. it is necessary to calculate the losses.7 SITE EVALUATION METHODOLOGIES 2. Consequently site selection is conditioned by the existence of both requirements.6. the losses for this project were calculated under design analysis. at a particular site over a period of years. 2. The flows over the years of river Nzoia were obtained from WRMA and the FDC of those values was plotted. From FDC the design discharge was read from the curve.5 Evaluation of gross head The gross head is the vertical distance that the water falls through in giving up its potential energy.1 Introduction Adequate head and flow are necessary requirements for hydro generation. 2. This makes hydropower extremely site dependent.6. will provide a table of discharges that can be organized into a usable form. The site evaluation was done to get the exact place to install power house and where to construct things like intake weir. handheld Global positioning system was employed to get gross head of this project at river Nzoia water fall. Hence.7.6. the proportion of time during which the discharge there equals or exceeds certain values. Sufficient and dependable stream flow is required. pipe friction. 2. WRMA has gauged river Nzoia and they take reading everyday throughout the years.All hydroelectric generation depends on falling water. 2. Hence. 8 . 2.6 Estimation of net head Having established the gross head available.3 Stream Flow Characteristics A program of stream gauging.2 Stream flow records In Kenya. Turbines that operate in this way are called reaction turbines. which provide a series of formulae by analyzing the characteristics of installed turbines. Photograph 2.8. some preliminary design rules and some selection criterion. They are usually used for head ranges from 25 to 350 m. fore-bay settling basin. ELECTROMECHANICAL EQUIPMENT This chapter gives the main description of the electromechanical equipment. tailrace and powerhouse. 2.8.8. Lugaresi and Massa14 15. used for medium heads.and channel. Belhaj18. Based on the formulae given by the authors above Francis turbine was chosen for this project. penstock. must be strong enough to withstand the operating pressure. 2. The details about Francis turbine are given below. 2. Francis turbines Francis turbines are reaction turbines.2 Hydraulic turbines Hydraulic turbines transform the water potential energy to mechanical rotational energy.8. Gordon19 20. Formulae are based on work undertaken by Siervo and Lugaresi11.8 shows a horizontal axis Francis turbine. All the formulae of this chapter use SI units and refer to IEC standards (IEC 60193 and 60041). The turbine casing.1 Types and configuration The potential energy in water is converted into mechanical energy in the turbine by: The water pressure can apply a force on the face of the runner blades.1 Powerhouse The role of the powerhouse is to protect the electromechanical equipment that convert the potential energy of water into electricity. 2. The topographic of the site was considered and geological area of the site dealt with to give easier for construction. spillways. Austerre and Verdehan16. 9 . which decreases as it proceeds through the turbine. In this turbine water entry is radial but exits axially. Siervo and Leva12 13. Schweiger and Gregori21 22 and others. Francis turbines belong to this category. with the runner fully immersed in water. Giraud and Beslin17. with fixed runner blades and adjustable guide vanes.2. Photo 2.8. 2. An efficient draft tube would have a conical section but the angle cannot be too large. 2. The kinetic energy is proportional to the square of the velocity. The optimum angle is 7º but to reduce the draft tube length. sometimes angles are increased up to 15º. Hence. without any doubt more precise than the conventional enveloping curves. and therefore its cost.8: Horizontal axis Francis turbine The draft tube of a reaction turbine aims to recover the kinetic energy still remaining in the water leaving the runner. a draft tube is required to reduce the turbine outlet velocity.4 Turbine selection criteria The type. just mentioned. otherwise flow separation will occur.3 Specific speed The specific speed constitutes a reliable criterion for the selection of the turbine.8. geometry and dimensions of the turbine will be fundamentally conditioned by the following criteria:  Net head  Range of discharges through the turbine 10 . It is necessary to know the flow regime. The net head is the ratio of the specific hydraulic energy of machine by the acceleration due to gravity. as the remaining kinetic energy in low head schemes cannot be neglected.8.3 Cavitation When the hydrodynamic pressure in a liquid flow falls below the vapor pressure of the liquid. 2.4.4.8.8. The cavitation calculation is dealt with under design analysis.1 Net head The gross head is well defined.4.8. as the vertical distance between the upstream water surface level at the intake and the downstream water level for reaction turbines or the nozzle axis level for impulse turbines. there is a formation of the vapor phase. commonly represented by the Flow Duration Curve (FDC) as explain earlier under stream flow evaluation.2 Discharge A single value of the flow has no significance. 2. This definition is particularly important.  Specific speed  Rotational speed  Cavitation problems  Cost 2. 2.4 Rotational speed The rotational speed of a turbine was calculated to be 354 rpm but that speed was very low for generator to do direct coupling hence the speed increaser was used to step off the speed of generator 11 .4. The first criterion to take into account in the turbine's selection is the net head. The formation of these bubbles and their subsequent collapse gives rise to what is called cavitation. This phenomenon induces the formation of small individual bubbles that are carried out of the low-pressure region by the flow and collapse in regions of higher pressure. 8. an exciter is necessary for supplying field current to generator and keeping the output voltage constant even if the load fluctuates.8. Table 2. 12 .8.7. cavitation. 2. that can strongly reduce the yearly production and damage the turbine.9 shows this ratio for miscellaneous turbines.1 Type of Generator Synchronous generator was selected due to its advantages compare to asynchronous.g. 2. 2. it can attain 2 or 3 times the nominal speed. which the unit can theoretically attain in case of load rejection when the hydraulic power is at its maximum. 2.8.7 Generators 2. belt speed increaser was selected.2 Exciters In case of synchronous generator. Depending on the type of turbine. The turbine efficiency was chosen from the best practice of Francis turbine. vibration.7. the speed increaser was adapted to increase the speed of generator to the required speed without directly coupling the two.8. since they must be designed to withstand it.6 Turbine efficiency The efficiency characterizes not only the ability of a turbine to exploit a site in an optimal manner but also its hydrodynamic behavior. But only manufacturers can provide the most reliable efficiency for the turbine. Average efficiency means that the hydraulic design is not optimum and that some important problems may occur e. etc. It must be remembered that the cost of both generator and eventual speed increaser may be increased when the runaway speed is higher.5 Runaway speed Each runner profile is characterized by a maximum runaway speed. Independent exciter of rotor is provided for each unit Applicable for both independent and existing power network. Hence. This is the speed.7 Speed increasers Due to low rotational speed of Francis turbine for this design.2.8. Thus.8 Automatic control Small hydro schemes are normally unattended and operated through an automatic control system.8. Because not all power plants are alike.8.8. regulating the voltage. According to this project the plant is going to operate in such a way that the safety is first priority during operation.Synchronous generators The synchronous generator is started before connecting it to the mains by the turbine rotation.7. If 13 . it is almost impossible to determine the extent of automation that should be included in a given system. switchgear must be installed to control the generators and to interface them with the grid or with an isolated load. independent of the load. frequency. controller and operation. 2.1 Plant service transformer Electrical consumption including lighting and station mechanical auxiliaries may require from 1 to 3 percent of the plant capacity. 2. the voltage controller maintains a predefined constant voltage. In the case of an isolated or off grid operation. the controller maintains the predefined power factor.8. 2.3 Speed Governors It is adopted to keep the turbine speed constant because the speed fluctuates. Also metering equipment must be installed at the point of supply to record measurements according to the requirements of the electric utility. 2. water head and flow. the higher percentage applies to micro hydro (less than 500 kW). When all these values are controlled correctly. the generator can be switched to the grid. By gradually accelerating the turbine. Hence Dummy load type was adapted.4 Switchgear equipment In many countries the electricity supply regulations place a statutory obligation on the electric utilities to maintain the safety and quality of electricity supply within defined limits. Kenya is not exception in this obligation. changes in load.8. In case of the mains supply. phase angle and rotating sense. the generator must be synchronized with the mains. The governor consists of speed detector. The change of generator rotational speed results in the fluctuation of frequency.7. The service transformer must be designed to take these intermittent loads into account. possible.8. In powerhouses provided with automatic control the best solution is to use transducers connected to the computer via the data acquisition equipment.8.8. a board marked with meters and centimeters in the style of a leveling staff. however someone must physically observe and record the measurements.2 DC control power supply It is generally recommended that remotely controlled plants are equipped with an emergency 24 V DC back-up power supply from a battery in order to allow plant control for shutdown after a grid failure and communication with the system at any time.9 ENVIRONMENTAL IMPACT AND ITS MITIGATION 2. inserted on an irrigation canal or built into a water supply system produce very different impacts from one another. 2. from both a quantitative and qualitative viewpoint. full control is ensured for as long as it may be required to take corrective action. provisions should be made to record both the headwater and tail-water.9. securely in the stream. should be used to ensure service in an unattended plant. 14 . with automatic changeover. Even the location of the powerhouse will be at the base and shall not alter the ecological system. The ampere-hour capacity must be such that.2 Impacts in the construction phase Schemes of the diversion type. multipurpose reservoir. A high mountain diversion scheme situated in a highly sensitive area is more likely to generate an impact than an integral low-head scheme in a valley.8. The simplest way is to fix.3 Headwater and tail-water recorders In a hydro plant. 2. 2. two alternative supplies.1 Burdens and impacts identification Impacts of hydropower schemes are location and technology specific.9. on loss of charging current. 2. 4 Impacts arising from the operation of the scheme 2. from the speed increasers. color or textures. open canals. the high noise level and other minor burdens contribute to damaging the environment when the scheme is located in sensitive areas. In view of its protective role against riverside erosion it is wise to restore and reinforce the riverbank vegetation that may have been damaged during construction of the hydraulic structures. intake. even the largest. To mitigate such impacts it is strongly recommended that the excavation work should be undertaken in the low water season and the disturbed ground restored faster. 2. penstocks. tailrace. Most of these components.powerhouse. danger of erosion due to the loss of vegetation through excavation work. with the intake.3 Water intakes. 2. The design. and tailrace and transmission lines must be skillfully inserted into the landscape. tailraces The impacts produced by the construction of these structures are.4. if necessary.2 Landscape impact Each of the components that comprise a hydro scheme .1 Sonic impacts The allowable level of noise depends on the local population or isolated houses near to the powerhouse. the penstock. may be screened from view using landscaping and vegetation. almost imperceptible when outside. etc. penstock. lines. weir. The noise comes mainly from the turbines and. when used. To mitigate the above impacts the traffic operation must be carefully planned to eliminate unnecessary movements and to keep all traffic to a minimum. location. best adapted to the local conditions. and appearance of any one feature may well determine the level of public acceptance for the entire scheme. spillway. The ground should be repopulated with indigenous species.9. to levels in the order of 70 dB. and substation and transmission lines .9.9. excavation dust. Nowadays noise inside the powerhouse can be reduced.4. turbidity of the water and downstream sediment deposition.has potential to create a change in the visual impact of the site by introducing contrasting forms. noise affecting the life of animals. The powerhouse. 15 . Vehicle emissions.9.2. or in extreme cases burying it.9.5. The lower flow can result in stranding newly deposited fish eggs in spawning areas.9. 2. 5 Biological impacts 2.6.2 Health impact In addition to the visual intrusion. which removes material from water in order to avoid it entering plant waterways and damaging electromechanical equipment or reducing hydraulic performance. 2. These impacts can be mitigated by adapting the line to the landscape.5.9. peaking can result in unsatisfactory conditions for fish downstream because the flow decreases when the generation is reduced.2.1 Visual impact Above ground transmission lines and transmission line corridors can have a negative impact on the landscape. some people may dislike walking under transmission lines because of the perceived risks of health effects from electromagnetic fields.9. 2.9.2 Trash-rack material Almost all small hydropower schemes have a trash rack cleaning machine.6.9. The eggs apparently can survive periods of de-watering greater than those occurring in normal peaking operation but small fish can be stranded particularly is the level fall is rapid. 16 .6 Impacts from transmission lines 2.1 In the reservoir In integral low head schemes. 94 (Francis turbine) Transmission efficiency. t= 0.992.89 * 1000 P = 9.5 m and design discharge = 21m3/s 3.81 * 21 * 54.1 Determination of power output P=g*Q*H* o * ρW Where P = power developed g = gravitational acceleration Q = design flow rate H = head o = overall efficiency ρW= density of water In our case. g = 0. The analysis is done using some empirical formulae from reference materials cited under references.CHAPTER 3.5 * 0. power developed by generator is given by.89 Thus. The design analysis is based on net head and design flow obtained earlier on in previous chapter.97 * 0. Turbine efficiency. Hence. m= 0.1 Design of electromechanical equipment 3.97 (synchronous generator) Hence o= t* m * g o= 0.1.98 (Belt type) Generator efficiency.515 W P = 9.992MW P ≈ 10 MW 17 . the net head = 54.98 o= 0. P=g*Q*H* o * ρW P = 9.94 * 0.0: DESIGN ANALYSIS In this chapter we are going to carry out analysis on the small hydropower components. rotational speed.2 Design of Francis turbines After the analysis. Turbine type Best efficiency Kaplan single regulated 0. power output and cost. flow rate.85 Table 2.93 Francis 0.94 Pelton n nozzles 0.89 Turgo 0. The selection was arrived at using charts and tables as shown below.3.6: Range of heads 18 . specific speed.10: Typical efficiencies of small turbines Turbine type Head range in metres Kaplan and Propeller 2 < H < 40 n Francis 25 < H < 350 n Pelton 50 < H < 1'300 n Crossflow 5 < H < 200 n Turgo 50 < H < 250 n Table 2.90 Pelton 1 nozzle 0.91 Kaplan double regulated 0. the Francis turbine was selected using net head. 6 Q = 21m3/s 19 .5 m E = g * Hn= 9. 3.2484 For Francis turbine the range of specific speeds is: 0. NS NS = 1. N N =NS* E3/4 / √Q But Hn= 54.924 / (54.5 = 534.2.924 / Since Hn= 50m = 1.33 Hence the specific speed is within the range thus acceptable.1 Specific speed.0η ≤ NS ≥ 0.5)0.81 * 54.512 = 0.These calculations are based on Lugaresi and Massa equations. 3.2.2 Rotational speed. 026 t/s Where t/s is turn per second.3 Dimensions of Francis turbine Outlet diameter D3 is given by.2484)) * √η4.5 * (0.η/ (θ0 * θ.488 * 0. Therefore in RPM is given below.601 m 20 . D2 = D3/ (0.75 / √21 N = 6.5 * (0.095/ Ns) * D3 The inlet diameter D2 is given by. But N is always given in RPM. N = 6.31 + (2.6) 0.164. D3 = 84.4 + 0.2.488 * NS)) * √Hn/ (60 * N) Inlet diameter D1 is given by.3781 * Ns) For NS<0.96 + 0. D1 = D2 Using the above equations the diameters of the runner of Francis turbine are: D3 = 84. D1= (0.026 RPS * 60 seconds / minute N = 361.56 RPM 3.31 + (2.Hence N = 0.02θ) D3 = 1.2484 * (534. 4 + 0.15 to 0.1 to 0.45 Flow ratio. Speed ratio. all these dimensions of diameters are given in figure of Francis turbine runner under literature review above. n = B2 / D2 Where the value of n varies from 0.2484) D2 = 1.3781 * 0.601 / (0. Ku = u / (√ (2gH)) The value of Ku ranges from 0.253 m D2 = 1. (B/D) n = B1 / D1.601 D1 = 1. Ratio of width to diameter.2484) * 1. Kf= Vf1 / √ (2gH) The value of Kf varies from 0. D1 = (0.30 Speed ratio Ku The speed ratio is the ratio of peripheral speed at the inlet to the theoretical velocity.6 to 0.96 + 0.519 m Hence. Thus. Flow ratio. Kf The flow ratio is the ration of the velocity of flow at the inlet to the theoretical jet velocity.095/0.9 Using above equations yield: 21 . Thus. 3 * √ (2 * 9.58 – 30.81 / (16.ηθ / 60 u1 = 30.58 m/s Guide vane angle (α) and the runner vane angle ( ) Tan α = Vf1 / Vw1 = 9.31)) = -35.94 Therefore Vw1 = 0.81 * 54.81 / (16.81 * η4.η) Vf1 = 9.31) Tan-1(9.7205 m Flow velocity.31 m/s Velocity of whirl at inlet Vw1 L= Vw1 * u1 / (g * h) Vw1 = L * (g * h) / u1 Since the best efficiency of the Francis turbine is L= 0.5 / 30.45 * 1.31 Vw1 = 16.θ01 * 3θ1. u1 u1 = π * D1 * N / 60 u1 = π * 1.45 22 . Tan = 9.Width B1 B1 = 0.81 m/s Rim velocity (tangential).601 m B1 = 0.58 – 30.58 Tan-1(9.5° Width at outlet n =B2 /D2 where n = 0.94 * 9. Vf1 Vf1 = Kf√ (2gH) Vf1 = 0.81 / 16.58) α = 30.81 / 16.θ° But Tan = Vf1 / (Vw1 – u1) So. 8° 3.94 / 28.ηθ / 60 u2 = 28.47 m/s Guide vane angle (ϕ2) and the runner vane angle at the outlet (β2) = 90° Tan ϕ = Vf2 / u2 Tan-1 (9.5 * 0.2484 Knowing the specific speed. The specific speed is a non-dimensional expression for rotational speed at a given head at best efficiency point. the required NPSH can be calculated as.76 m/s Velocity of whirl at outlet (Vw2) Vw2 = g * H * h/ u2 Vw2 = 9.45 * 1. u2 = π * D2 * N/60 u2 = π * 1. 23 .76 Vw2 = 17.η19* 3θ1.6836 m Hence u2 is given by.81 /28.2. the turbine can be submerged.81 * 54. The required level of submergence. The impact of gas cavities collapsing close to the wall surface causes cavitation erosion. expressed as Net Positive Suction Head (NPSH) depends on the main dimensions and the speed number of the runner.So B2 = 0.45 * D2 B2 = 0. From previous calculation: NS =0.519 B2 = 0.76) ϕ = 18. cavitation may occur. In order to avoid the water pressure to drop below the vapor pressure.4 Cavitation design If the water pressure in the runner is lower than the vapor pressure. A negative value of Hs implies that the turbine is set below tail Water level.055 * (17.03625 bar 1 atm = 1.35 NPSH has to fulfill the following requirement to avoid cavitation NPSHrequired < hatm − hva − Hs hva from the steam table at a temperature of 24°c = 0.81) + 0.01325 bar hva= 0.03578 atm = 0. and. dependent on the speed number.3 .3685) 6.03625 bar / 1.Where the parameters a and b are empirical constants.931 thus no cavitation occurs. according to Brekke.81)2 / (2 * 9. NS<0.12 and b=0.1· NS Cm2 = Vf2 = flow velocity at outlet = 9. 1 atm = 10.0.601 m 24 .12 and b=0.1 Inlet diameter Di Di = 1. From the above calculation. Flare angle of 6° 3.35 < 9.3 Design analysis of the draft tube Conical Draft tube was selected for this design due to its advantages over other type.12 * (9.35 < (10.55 gives a=1.3.3 mWc hva= vapor pressure Hs= submerging of the turbine.3685 mWc 6.81) NPSHrequired = 6.81 m/s U2 = Vw2 = whirl velocity at outlet =17. 3. Where hatm= atmospherically pressure.55 gives a=1.47)2 / (2 * 9.01325 bar * 1 atm hva= 0.47 m/s NPSHrequired = 1. Thus submerging the turbine below the tailrace water level is not necessary to avoid cavitation. the turbine is not subject to cavitation even without being submerged.055 NS>0. 9256 m D0 = 0.Vertical height of draft tube y = 2.4628 m Total increment = 0. Consider the triangle below.75 * Di y = 2. Tan 6° = x / y but y = 4.9256 m + 1.601 m D0 = 2.3.2 Exit diameter of draft tube.5266 m 25 .601 m y = 4.403 x = 4.403 m Tan 6° = x / 4.75 * 1.4628 m * 2 = 0.403 m 3.403 * tan 6° x = 0. 3.3.3 Tail race water level, T T = 0.8 * Di T = 0.8 * 1.601 m T = 1.2808 m 3.4 Generator Design 3.4.1 Number of poles Np= 120 * f / N Where Np= number of poles F = frequency of supply i.e. 50 Hz in Kenya N = rotational speed (RPM) Np= 120 * 50 / 361.56 Np= 16.59 ≈ 17 poles Table of Standard Rotational Speed of Generator Referring to the original turbine speed and the rated generator speed, either direct coupling or indirect coupling with power transmission facility (gear or belt) is selected so that the suitable ratio of speed between turbine and generator can be matched. The total cost of turbine, transmitter and generator shall also be taken into consideration. For small hydropower plant, 4 – 8 poles are selected to save the cost. Hence, 17 poles are not economically. Therefore, the speed 26 increaser is used to raise the speed of turbine to the standard speed of generator without directly coupling the two. Since the speed of the turbine was calculated as 362 RPM, it is seen that this speed is low and hence needs to be increased. The ideal speed can be achieved by increasing the rotational speed of turbine by a factor of four. 3.4.2 Speed of generator Ideal speed = 4.1 * 362 = 1484.2 RPM ≈ 148η RPM Hence Np= 120 * f / N Np= 120 *50 / 1485 Np= 4.04 poles ≈ 4 poles For small hydropower plants, 4 – 8 pole generators are selected to reduce the cost of the generator. The size and cost of high speed generators is less in comparison to low speed generators. Hence, 4 poles fall within acceptable limit and results to a cheaper generator. The type of coupling to be used is the flexible coupling of belt drive to increase the speed of turbine to acceptable speed of generator. 3.4.3 Exciter of generator In the case of a synchronous generator, an exciter is necessary to supply the field current to the generator and keep the output voltage constant even when the load fluctuates. Type of exciters i. Brush type ii. Brushless type For small hydropower plants the brushless type of exciter is recommended due to its low maintenance costs. The best efficiency of this type of generator is 97%. 3.4.4Generator type A synchronous generator with three phases is selected because it is economical and most reliable. 27 3.4.5Generator output The output of the generator is shown in KVA and calculated as follows; Pg (KVA) = 9.81 * H * Q * o* ρ / Pf Where Pg = required power output H = net head Q = design discharge (m3/s) o=overall efficiency i.e. turbine efficiency, t*transmission efficiency, m * generator efficiency, g ρ = density of water Pf= power factor = 0.8 Hence Pg (KVA) = 9.81 * 54.5 * 21 * 1000* 0.89/ 0.8 Pg (KVA) = 12,490 KVA Pg (KVA) ≈ 12,η00 KVA 3.5 Power transmission facility (speed increaser) The speed increaser is always used to reduce the set-up cost especially when the turbine speed is very low. Hence, the speed of the turbine is stepped up by a factor to a certain convenient value. For this design a factor of 4.1 is adopted to increase the rotation speed. This saves on cost since low speed generators are big and expensive. In addition to this, in the case of small- hydropower plants, V- belts or flat belts coupling are usually adopted to reduce overall costs since gear type transmissions are very expensive. The efficiency of the belt type transmitter for this design is 98%. 3.6 Control facility of the turbine and generator. 3.6.1 Speed governor The speed governor is adopted to keep the rotation speed of the turbine constant. The change in the speed of rotation of the turbine is due to changes in load, water head and water flow rate. 28 For this design.2 Determination of the penstock thickness.7.7 DESIGN OF CIVIL STRUCTURES 3.F = safety factor according to the cooling method being employed (1.5 m/s This is from common practice that flow velocity in small hydropower plant penstocks’ range from 2 m/s to 5 m/s.2 – 1.2 Making D the subject D = 2* √ (A / π) D = 2* √ (4.7.θθ7 / π) = 2. Pd= Pg * Pf * S. Q = 21 m3/s Net Head = 54.5 MVA * 0. A= Q / V A = 21/ 4.4 m 3.4 Pd= 14 MW 3. tp tp = P * r / σ 29 .5 m Penstock flow velocity = 4.F Where Pd= capacity of the dummy load Pg = rated output of the generator Pf = rated power factor of the generator S.437 m Thus D ≈ 2.4) Pd(KW) = 12. a dummy load type governor is recommended since it is cheap. Find internal diameter.5 = 4. The capacity of the dummy load is calculated as follows.8 * 1.667 m2 But area of a circle Or A = πD2/4.1 Penstock hydraulic calculations In our case. P =Ph + Ps Where P = total pressure Ph = pressure due to water hammer Ps = static water pressure σ = stress P h = ρw * Cp * V For water under ordinary conditions.5 Ph= 5. Cp= 1120 So. Ps Ps = ρw* g * H Ps = 1000 * 9.81 * 57 Ps = 0.5572 MPa Factor of safety. n = 4 σyp= 957MPa But P =Ph + Ps P = 5.4 / 2) / (239.157 * 106 * (2.25 MPa Hence = P * r / σallowable = 6. Ph= 1000 * 1120 * 4.04 MPa Static pressure.6 + 0.5572 P = 6.25 * 106) 30 .157 MPa σallowable = σyp / n = 957 * 106 / 4 σallowable = 239. 81) hV= 0.9 / 2.2064 m hVT≈ 0.5 m Hence.093 m + 0.7.42 m + 0.7.com/moody.88 mm ≈ 31 mm 3.θ7θ m Total head losses in the.3 Head loss in the penstock 3.7.2 * (4.25 / (2 * 9. The head losses were calculated from above.311 m hT = 2.4) * (20.3 Head loss due to friction.1 Head loss due to entry and exit.7.php This enabled us to get the value of ‘f’ from the Moody’s chart more accurately.42 m 3.09 hb= 0.5 m.03088 m = 30.093m 3.2 Head loss due to bend.009 hf= f * (LP / DP) * (V2 / (2 * g)) hf= 0.3. tp= 0. the gross head from the site was 57 m and the net head is found by subtracting the head losses.09 * 20.5 = 54.2 hV= 0.2064 m But two valves lie at the entry and exit.5)2 / (2 * 9.lmnoeng. hf hf= f * (LP / DP) * (V2 / (2 * g)) N/B: For the purpose of accuracy we used the program from the website www. Net head is 57 – 2. hV hV= K * V2 / (2 * g) But K = 0. hT hT = 1.81)) hf ≈ 1. f = 0. hVT= 2 * 0.3.25 / (2 * 9.009 * (432.676 m + 0. 31 .3. hb hb= C * V2 / (2 * g) For a deflection angle of 45° C = 0.81) hb= 0. hL ≤ 0.0η * η7 m 2. For rectangular channel section.015 The most economical channel shape is rectangular.5/0.8η m From the above rule the head loss comply with it hence the design is safe.015 h = 2. 3.7.5 ≤ 2. h = b / 2 and R = h / 2 Hence A=b*h But h = b / 2 or b = 2 * h Thus A = 2h2 Therefore Q = A * R2/3 * /n 21 = 2h2 * (h/2)2/3 * (1/1500)0.1314 m 32 . The rectangular channel cross section is most economical when.5 ≤ 0.4 Design of head race (open channel) Q = A * R2/3 * /n Where Q = design discharge of head race = 21 m3/s A = area of the cross section = b * h b = width of the channel h = depth of the channel R=A/P P = wetted perimeter = b + 2h SL= longitudinal slope of the head race ≈ 1/1η00 n = coefficient of roughness = 0.From the design rule.0η Hgross 2. 3.1 Weir height calculations Under normal conditions.Hence b=2*h b = 2 * 2.5 Intake Weir (Dam) 3.0 m/s) Qd= A * V But Qd= 21 m3/s V = 1 m/s A = 21m3/s / 1 m/s = 21 m2 A = b * hi = 21 m2 We choose b = 5 m Where b = width of the side intake hi= height of the side intake hi= 21 / 5 hi= 4.7. the weir height should be planned to exceed the calculated value by the following method to ensure the smooth removal of sediment from the upstream of the weir and the settling basin.1314 m b = 4.5 – 1.7. d1 = height of the bed of the scour gate to the bed of the inlet (usually 0. 3.0 m) hi= water depth of the inlet ( usually determined to make the inflow velocity approximately (0. D1 = d1 + hi Where.5 – 1. determined in relation to the bed elevation of the scour gate of the intake weir.6 Side intake Weir height.2 m 33 .5. D1.2628 m The length of the channel will be measured at the site to get accurate one.7. 1 m/s for a target grain size of 0. V = 0. Ls.8 Head tank Function of the head tank.θ / 0. L ≥ (V / υ) * hs Ls = 2 * L Where L = minimum length of the settling basin (m) Ls = length of the settling basin hs= water depth of the settling basin (m) υ = marginal settling speed for sediments to be settled (m/s). flow velocity. is usually determined so as to incorporate a margin to double the calculated by the formulae below.1) * 5 Ls= 30 m * 2 = 60 m 3.6 m/s is tolerated in the case where the width of the settling basin is restricted. It is usually around 0. etc. The minimum length (L) is calculated by the following formulae based on the relation between the settling speed. The length of the settling basin.η – 1 mm).6 m/s b * hs= 21 / 0. L ≥ (V / υ) * hs L ≥ (0. and the water depth.  Finally remove litter (sand. Qd= design discharge (m3/s) b = width of the settling basin (m) but Qd= 21 m3/s .7 Settling basin design The settling section’s function is to settle sediments / grain size of (0. drift wood. 34 .7. V = mean flow velocity in the settling basin (m/s). V = Qd / (b * hs) Where.0 mm. υ.7. hs.3. V.3 m/s but up to 0.5 to 1.6 = 35 m2 We choose b = 7m and hs= 5 m.) in the flowing water. it is usually around0.  Control the difference of discharge in the penstock and the head race because of the load fluctuations. Vsc= As *dsc= B * L *dsc Where.8.7 m2 dsc= ho / 2 Where.05 m Therefore L = 48.837 m2 / 1.3 = 8.3. Vsc= B * L *dsc= 420 m3/s B = 2 * 4.5 m The dimensions of the head tank were chosen as a matter of convenience. ho= height of the head race = 2.7.6 = 48.05 m = 46.6 m L * dsc= 420 / 8. 35 .1 / 2 = 1.1 m Hence dsc= 2. In the case where only the load is controlled Vsc= 20 * Qd Vsc= 20 * 21 Vsc= 420 m3/s The head tank capacity should be secured only to absorb the pulsation from the head race that is about 10 times to 20 times the design discharge (Qd). Vsc=head tank capacity dsc=water depth from uniform flow depth of a head race when using maximum discharge (ho) to critical depth from top of a dike for sand trap in a head tank (hc). B = width of the head tank L = length of the head tank Determine the head tank capacity.1 Head tank capacity Definition of the head tank capacity The head tank capacity is defined as the water depth from hc to ho in the head tank of length L as shown in the diagram.5 m L = 46. 1.000. the preliminaries for civil works cost was approximated to be KSHS 4.031 M 36 .4 Fore-bay From cost analysis of projects of similar size.00 = 1. the penstock civil works cost was approximated to be KSHS 700.00 4.1 Preliminaries (for civil structure work) From cost analysis of projects of similar size.3 Settling basin From cost analysis of projects of similar size.1.000.500.00 4.00 4.500.000.1.1 DIRECT COST 4.000.5 metres was approximated to be KSHS 2.1.4 M Length of penstock (LP) = 432.9 M Thickness (tp) = 31 mm = 0.200.00 4.000.000. the fore-bay cost of length 46.1.000.1.000. the intake weir construction cost was approximated to be KSHS 5.00 Kshs 1. the settling basin cost of length 60 metres was approximated to be KSHS 3.000.7 Penstock pipes Internal Diameter (Di) = 2.1.000.CHAPTER 4: PROJECT COST ESTIMATION This chapter is dealing mainly on the estimate cost of the project if the implementation is going to take place.6 Penstock civil work From cost analysis of projects of similar size.2 Intake weir From cost analysis of projects of similar size.500. 4.00 4.5 Spillway Length of spill way = 15 M Cost per metre = KSHS 100.00 4.00 Total cost = 15 * 100.500. the low slope canal of length 503.698.000.000.1.000.000.500.000.12 Transmission line From cost analysis of projects of similar size.298.925 =KSHS 12.00 4. The total cost was thus KSHS 35.875.00 Total civil works The total cost of the civil works was the sum of the above mentioned nine components.1. the power house construction cost was approximated to be KSHS 4.5 kilometres was approximated to be KSHS 18.4 + 0.00 4.Density of steel = 8000 kg / M3 Price of steel = Kshs 15 per kg Volume of steel = Π * Lp * (((Di + 2 * tp)/2)2 – (Di / 2)2) = Π * (((2.10 Francis turbine This price was found directly from one of the turbine manufacturers called Saimpro hydraulics.1.1. the transmission line of 1.925 kg Cost = (price / kg) * mass =15 * 819.1.5 M cost was approximated to be KSHS 2. Turbine cost = KSHS 94.11 Synchronous generator The price was found from Siemens alternator manufacturer.9 Volume of steel = 102.000.031 * 2)/2)2 – (2. The exchange rate used was 1pound = kshs 147 4.00 4.000.00.5 M3 Mass = density * volume = 8000 * 102.750.8 Canal From cost analysis of projects of similar size.4 / 2)2) * 432.00 37 .5 = 819.000.000.9 Power house From cost analysis of projects of similar size. Hydropower generator unit cost = kshs 23.00 4. 000.2 Contingencies Approximately 10% of direct cost = 10% * Kshs 174.3 Administration Approximately 7% of direct cost = 7% * Kshs 174. This produces a sum total of KSHS 212.2.00 4.200. the construction supervision cost was approximated to be KSHS 3.4.00 Total of indirect cost The total indirect cost of the above elements was found to be Kshs 38.000.000.000.00 = KSHS 8.1 Engineering cost Approximately 5% of direct cost = 5% * Kshs 174.324.13 Construction supervision From cost analysis of projects of similar size.524.00 38 .000.00 = KSHS 12.00 Total direct cost The total direct cost of the above components was found to be Kshs 174.00 4.000.00 4.2.000.200.2 INDIRECT COST OF CONTRACTOR 4.000.00 = KSHS 17.000.200.200.000.710.2.1.420.194.000.00 Total cost of project The total cost of the project is the sum of direct and indirect costs. the area has many industries working there and it host pan Africa paper mill which was supplying books in the region. Conclusions and Recommendations 5. After we got the FDC we read the design flow rate from the curve and it became our design flow rate of the river. We took the measurement of head at difference point upstream where to locate the intake and downstream where to put powerhouse which will house electromechanical equipment. As we know when the river level goes down to predetermine level.1 DISCUSSION The object of this project was to carry out design of small hydropower at River Nzoia at Webuye East constituency in Bungoma county western Kenya. we got the data pertaining river Nzoia and we have to take them for analysis in form of flow duration curve (FDC). Besides. Being the current problem to be tackle. the choice of the flow rate of 39 . we got the gross head as the difference of head upstream above sea level and downstream above sea level. Webuye has market and commercial centers and lodges and hotel around. Also the river was having gauging station done by water resource management Authority which takes reading on daily basis to yearly. that is the purpose of this project to address the challenge and provide the sustainable and most reliable power. The measurement of the head and the coordinates of the location were found by using GPRS. The area is very fertile as the local people around the river grow a lot of crops for subsistence and for commercial purpose. the flow of river will drop and the design flow become less than what was meant to drive turbine hence. The major challenge facing the local population around that area is lack of enough power and hence. The river itself has enough water to be used to generate enough electricity for use in the area and the surplus can be injected in to the national grid for sale. Thus. Therefore. we therefore went to the site to assess the potential site for installation of hydropower plant. Hydropower is the most clean renewable source of energy compare to other source of power. River Nzoia has water fall near the station of Nzoia Water Company the only water plant in Bungoma supplying clean water to many areas in Bungoma County and beyond.0: Discussion. This is a curve generated by plotting the flow of the river recorded daily for duration of many years. the turbine will not work and the plant will be shut down with immediate effect. However. Our aim was to get the location that will give us the maximum head and to be economical too in term of construction cost.CHAPTER 5. The generator type was synchronous type of three phase.the river plays a very critical role in the plan of the small hydropower to eliminate the shutdown of the plant. generator and its accessories. The turbine was chosen among the other variety of turbines using certain criterion e. However.g. The design was divided in to two major parts i. Again the cost of generator goes hand in hand with the high speed of generator. specific speed. the specifications of generator are given above. are supposed to be within a range of 4-8 poles. penstock. flow rate. net head. The cost of the project was estimated under the chapter of cost estimate. intake. powerhouse foundation and power house building) and electromechanical equipment (turbines and its accessories. channel. After getting flow rate and the net head (which was found after subtracting all the losses along the components) then the actual plan went ahead and the power output was calculated safely. The specifications of each after design are listed under summary section of chapter 5. control system and transmission line).e. settling basin. rotation speed. And at the same time the number of poles for small hydropower of generator. power output and above all the cost. speed increase to top up the speed to the speed of generator in the market. the site is economical viable for the generation of electricity of more than what is given in this project if other points on the site where to be chosen for installation of power house and the intake point. the design of civil structures (intake weir. After using all those criteria with the help of chart and table in the section of electromechanical above the Francis turbine met almost all the criteria for selection and hence for this project it is the recommended turbine. At the same time the speed of turbine was 362 RPM which was very low for generator. therefore we have to choose belt drive.1 to step up the speed of turbine to1485 RPM which is good enough for generator speed. spillway. head-tank /fore-bay. The project if implemented will generate enough revenue to the local around the area and local authority that can be enough for their development 40 . The number of poles of generator was calculated using the step up speed and frequency of 50 Hz for case of Kenya and we got the number of poles that fall within that range hence the design was safe. The turbine chosen was Francis turbine and again its specifications are list in summary section. The selection of dimensions and other specifications was not accidental it was after analysis and due to economical consideration. To achieve that we had to choose a factor of 4. But for contractor to get most reliable cost it will be in order to get the real cost at the site especially the civil structures location. It can provide electricity for local around the plant and beyond can enjoy the clean power for their daily up keep. It can always generate revenue to the central government.2m 1 3 Side intake Velocity = 1m/s 1 Width.2m 4 Settling basin Velocity.9 m 2 weir Height = 5. h = 4.1314 m 41 .6m/s 1 Width= 7m Height = 5m Length = 60 m 5 Channel: Length. b = 5m Height. Width. L= 503. 5.2628 m Masonry concrete. Depth. Number 1 Penstock( commercial steel) Internal diameter 2000 mm 1 Thickness 30. B = 4.8 mm Length 432.2m 1 Rectangular. etc. v = 0. agricultures.2 SUMMARY OF DESIGN The following is the summary of the design analysis no component Dimensions/ specifications. It can attract investor who can invest in the area and provide employment and cheap commodities to civil population around the area. H = 2.for things like more schools. roads. 54417 m Height = 4.05m Length.6 Head tank Head-tank capacity.28976 m 9 Generator (synchronous) Phase = 3 1 Pole = 4 42 .2596 Runner outer diameter D3 = 1. L = 46. t = 94% 8 Draft tube Flare angle = 6° 1 Inlet diameter.6 MW 1 Rotational speed = 354 RPM Specific speed = 0. Dsc= 1. T = 1.6122 m Runner Inner diameter D1 = 1. Vs= 420 m3/s 1 Depth.2 m Design flow = 21m3/s Guide vane inlet angle α = 31° Guide vane outlet angle ϕ = 22° Runner inlet width B1 = 0.43355 m Tail race water level. Di = 1.7 m Runner outlet width B2 = 0.55557 m Turbine efficiency.6122 m Outlet diameter. D0 = 2.5m Width. B= 8.6m 7 Turbine (Francis turbine) Shaft power= 9. 2 MW Frequency = 50Hz Generator efficiency. g = 97% Brushless type exciter Power factor Pf = 0. Hg = 57 m Net head. The site is capable of producing far more than 10 MW in our design criteria.3 MW) that can be injected in to the National grid to generate income for the local authority in the area. Hn = 54.7 MW) is less than the estimated output hence there is surplus power (5.3 CONCLUSION The objective of this project was to design for construction a small hydropower plant capable of producing 10 MW along river Nzoia at Webuye.8 10 Speed increaser Belt type 1 Speed increaser efficiency = 98% Ratio = 4.1 11 controllers Dummy load type 1 Dummy load capacity.5 m Total head loss Hl = 2. Rotational speed = 1400 RPM Rated power = 11. The revenue can be utilized for the 43 . Qd = 21 m3/s Gross head. The power consumption of Webuye (4.5 m 5. Pd= 12.88 KW Site configuration Design discharge.5 MVA Power output = 9. 5. The project when completed will be capable of generating a lot of revenue.The further detailed design needed is on civil structures preferably by civil engineers and surveyors as these structures are beyond the scope of this project. Thus.There is need creating a power distribution network beyond the powerhouse and this need further research on this project.This project is site specific hence we would encourage its fast implementation. 3. 44 . the objective of project was achieved. The summary of the design components of hydropower with their specifications are listed in the table under the summary section of this chapter. anything left out in this project is due to time constraints.The local government or any other agency should look for funding to implement the project since it is economically feasible.The river is capable of producing more than10 MW hence we recommend the changing of focus from small hydropower a medium hydropower plant.This project needed more time for a more detailed report to be created. It will also improve the living standards of the local people. 6. 4.benefit of the local community. 2. 5. Hence. All the specifications are provided above including the cost estimate of project. Also the scheme for this design will be run-of-river scheme as discuss above under literature review because it is cheaper to install and the nature of the river is capable of providing water.4 RECOMMENDATIONS The following are the recommendation we suggested: 1. 6. USBR. NRECA International Foundation.2011pp 867-946. “Hydraulic Engineering Systems”. “Guidelines for the Design of Intakes for Hydroelectric Plants”. 19θ4. (1998) European Small Hydropower Association (ESHA). 8. ASCE. Kenya Bureau of Standard. T. Actas de HIDROENERGIA 93. “Proceedings of the Symposium on the Design and Operation of Siphon Spillways”. “TLC for small hydro: good design means fewer headaches”. 12. “Hydraulic Design of Spillways and Energy Dissipaters”. Allen R. Inversin. manual guide 5. Munich. Denver Colorado. April 1988. H. Munet y J. K.REFERENCES: 1.E. ESHA 2004 4. Moore. Washington DC. 7. pp 1052-1171 2.. 2010. DEPARTMENT OF ENERGY UTILIZATION MANAGEMENT BUREAU Manuals and Guidelines for Micro-hydropower Development in Rural Electrification Volume I June 2009 3.C. Committee on Intakes. “Evaluation of Alternative Intake Configuration for Small Hydro”. HydroReview. Japan international corporation Agency. New Jersey 1987. 11. Rajput (2011). 10. Munich. 45 . G.P. 1978a. “Micro-Hydropower Sourcebook”. London 197η. Hita. Fluid mechanics and Hydraulic Machines4th edition. “Design of Small Canal Structure”. D. Guide on How to Develop a Small Hydropower Plant.C. Tung y otros. Prentice Hall Inc. British Hydrodynamic Research Association. Compas. 13. USBR. 199η. CelsoPenche. T. R.M. Actas de HIDROENERGIA 93. Huang and C. Washington. 9. Englewood Cliffs. “PCH de recuperation d’energie au barrage de “Le Pouzin””. Water Power & Dam Construction. June 1983 22. Gregory. 1989. “Applied Hydraulic Transients”. 1984.Gordon "A new approach to turbine speed". J. November 1987 46 . 1979. “Constructions Hydrauliques”. New York. F. August 1990 21.) “Manual de MinicentraisHidrelétricas. "Developments in the design of water turbines". Canadian Journal Of Civil Engineering. 24. "Designing Francis turbines: trends in the last decade".Gordon "Powerhouse concrete quantity estimates". H. G.Hidroenergia 1991. Water Power & Dam Construction September 1998. “Waterhammer Analyses”. de Siervo& F. May1989 23. “How to select your low head turbine”. J. 19θ3. Dover Publications. Bouvard. Lausanne. August 1976 25. 17. Inc. Water Power & Dam Construction. AA Balkema. Water Power & Dam Construction. M. Electrobras (CentraisEléctricasBrasileiras S. 20. 16. Parmakian. “Rubber seals for steel hydraulic gates”.L. 15. "Modern trends in selecting and designing Francis turbines".A.L. PPUR. 19. Massa. A Lugaresi& A. Chaudry. Hartl. de Leva. F. Schmausser& G. “Mobile barrages and intakes on sediment transporting rivers” IAHR Monograph.14. J. Van Nostrand Reinhold Company. Fonkenell.” 18. Sinniger& Hager. Water Power & Dam Construction. Schweiger& J. APPENDICES Photos of Nabuyole Falls 47 . 48 .