HS presentation .doc
- 1. University of Gondar Institute of Technology Design and construction of Water work assignment Section 2 Prepared by 1. birtukan zeleke 2. eden bekele 3. kidst agegn 4. Kibir molla 5. mahlet asefa 6. Mekdelawit merso 7. Wintana Getahun Submission date 27/11/2014 E. Submitted to:
- 2. Acknowledgement We would like to thank our teacher Instructor. who gave us this opportunity to work on this project. We have got to learn a lot from this project . We would also like to extend our heartfelt thanks to our seniors because without their help this project would not have been successful. Finally, we would like to thank our dear friends who have been with us all the time.
- 3. Definition of hydropower The hydropower plant or hydroelectric power plant is used to convert the kinetic energy of water into electric energy. The kinetic energy developed in the water flow due to the gravity of falling water from higher to lower head. The kinetic energy is used to rotate the turbine and the turbine is connected with an alternator to generate electrical energy. A hydroelectric power plant is a non- convention power plant and widely used to generate electricity from a renewable source of energy. To achieve kinetic energy from water, the reservoir or dam is constructed at a high head from the ground level. The initial cost of a hydroelectric power plant is very high. But the running cost is very low. In the world, 16% of total power is generated from the hydroelectric power plant. Components of hydropower plant The major components of the hydroelectric power plant are listed below. Dam Forebay Intake structure Penstock Surge tank Turbines Powerhouse Draft tube Tailrace
- 4. Dam The dam is the most important component of hydroelectric power plant. The dam is built on a large river that has abundant quantity of water through out the year. I should be built at a location where the height of the river is sufficient to get the maximum possible potential energy from water. Forebay The forebay is used to store water temporarily before passes to the intake structure. The forebay is an optional component of a hydroelectric power plant. The reservoir is used to store water across the river. In some hydroelectric power plants, the reservoir behaves as a forebay. And the water from the reservoir leads to the turbine. The amount of water stored in the forebay is decided based on the demand of required water and load in that area. Intake Structure The intake structure is a chain between the penstock and forebay. It collects water from the forebay and passes to the penstock. It plays an important role in power plants. The water comes in reservoir or forebay from the river. Therefore, the water contains much trash like trees and debris. The intake structure contains trash racks and placed trash racks at the entrance of the penstock. The trash racks are made of steel rods. It prevents severe damage to the turbine blades and nozzle. In trash racks, steel rods are placed with a gap of 10 to 30 cm apart.
- 5. Trash racks are heated in cols season to avoid ice rocks collision with turbine blade. Due to heat in trash racks, the ice rocks melted at the entrance of the penstock. The trash racks must be clean after a regular time period. And racks and trolly arrangements are used to clean the trash racks. Penstock Penstocks are used to increase the velocity of the water. It is large pipes laid on the slope. It carries water from the reservoir or intake structure to the turbine. The penstocks are open and close with the gate. So, at the time of opening and closing of gates, the pressure of water is very high. Therefore, the penstocks are designed to sustain the hammer of water. Short length penstock has heavy wall and long length penstock has surge tank is used to overcome the pressure of water. The penstock is made of steel and reinforced concrete. If the length of penstock is small, separate penstock is used for the turbine. If the length of penstock is large, a single penstock is used and at the end, it divides into branches. Surge tank A surge tank is a cylindrical tank or chamber placed near the powerhouse and it is connected with the penstock. The surge tank is also known as the surge chamber. It is used to control the pressure of water in the penstock. The water level of the surge tank increases when the powerhouse rejects the water due to low power demand. So, the surge tank controls the pressure in the penstock. When the power demand is high, a surge tank is used to accelerate the water flow. And in this condition, the water level of the surge tank is reduced. During steady load conditions, the water level becomes constant. Turbine
- 6. The turbine is used to convert the kinetic energy of water into mechanical energy. When the high-pressure water coming from the penstock strikes the turbine blade, the turbine starts rotating. The shaft is placed at the center of the turbine. And a generator is also connected with the same shaft and it further converts the mechanical energy into electrical energy. There are mail two types of the turbine; Impulse turbine Reaction turbine The impulse turbine is also known as a velocity turbine and the reaction turbine is also known as a pressure turbine. Powerhouse The powerhouse is used to provide support and housing to the hydraulic and electrical equipment. It is divided into two parts; substructure and superstructure. The substructure can be an integral part of the hydraulic system or it can be placed away from the hydraulic system. It is used to provide support to the equipment and provide necessary ways to the water. The superstructure contains the main unit and electrical accessories. The generators are placed on the ground floor with the turbine. Generally, for better visibility, the control room is placed on the first or second floor. Draft tube A draft tube connects the turbine outlet (turbine discharge) to the tailrace. To decrease the velocity of water, the width of the draft tube is gradually increased. The gates are provided at the end of a draft tube which is closed at the time of
- 7. maintenance. In the case of the reaction turbine, the draft tube is a necessary component. Tailrace The tailrace is a flow of water from the draft tube or turbine outlet. The powerhouse must be located near to the stream. If the powerhouse is placed far from the stream, it is compulsory to build a way or channel to flow the water into a stream. It will decrease the efficiency, cavitation, damage the turbine by silting caused unnecessary flow of water. Therefore, while designing a hydroelectric power plant, place the powerhouse near the stream. Sources of Energy Energy can be described as potential for work, which may be withdrawn if needed. The three most important and common sources, known as CONVENTIONAL are: Thermal power, Hydropower , and Nuclear power. The other sources of energy are also valuable, but in comparison to the main three sources, their contribution is limited – UNCONVENTIONAL : Tidal power Solar power Geothermal power Wind power , and Depression power.
- 8. Advantages and Disadvantages of Hydropower Hydropower has the following inherent advantages over other sources of energy Hydropower has a ‘perpetual’ source of energy, while thermal power has a depletable fossil fuel source Hydropower does not consume water;Running cost of hydropower plant is very low compared to thermal and nuclear plants Hydropower plants can be brought into operation in few minutes while thermal and nuclear power plants lack this capability. Thus, hydropower plants are particularlyuseful in taking up short period peak loads in a power grid system Efficiency of hydropower system is very high (80 – 90%), while thermal powe plants have low efficiency, as low as 40%; Hydropower development also provides secondary benefits such as recreation,fishing, flood control, etc, where storage is contemplated. Some of the disadvantages of hydropower development are: It is capital intensive and therefore rate of return is low; The gestation period (about 10 to 15 years between initial idea and final project inauguration) is long. This period is low for thermal power plants;
- 9. Hydropower is dependent on natural flow of streams. Since this is very variable the dependable or firm power is considerably low compared to total capacity Classification of hydropower Types of Hydropower Plant The hydroelectric power plants are classified into different types as follows. Based on the availability of water head Low head plant Medium head plant High head plant Based on the nature of the load Base load plant Peak load plant Based on the quantity of water available Run-off river plants without pondage Run-off river plant with pondage Storage type plant Pumped storage peak load plant Mini and micro hydel plant Based on the Availability of Water Head According to the available water head, the power plants classifies into three types, Low head plants
- 10. In this type of hydroelectric power plant, the available water head is less than 30m. In this type of plant, by constructing a dam, the water is stored. And the power plant is constructed at the base of the dam. If the excess water is available in the dam, it will flow over the dam itself. In this type of plant, Francis, propellor, or Kaplan type turbines are used in most of the cases. Medium head plant The hydroelectric power plant which has an available water head of 30m to 100m is considered a medium head plant. In most cases, the Francis turbine is used in this type of power plant. High head plant The hydroelectric plant having an available water head is more than 100m consider a high head plant. In this type of plant, a bulk amount of water is available in the dam from the rain or melting of snow. These plants are constructed in hilly areas to achieve high water head. In most cases, these plants are constructed on big rives in which the water is available throughout the year. The high head plant uses Francis turbine up to the head of 300m and Pelton turbine uses if the available water head is more than 300m. Based on the Nature of the Load Two types of load can be connected with the power plant. The plant running continuously throughout the day is said to be a base load plant. And the plant which is used to meet the peak demand is known as peak load plants. According to the type of load connected with the plant, the hydroelectric plants are classified into two types;
- 11. Base load plant These plants are used to take a load on the base portion of the load curve of the power system network. The base load plants are large capacity plants as it is built to meet the demand of the base load. The load factor of these plants is very high. In most cases, these plants are runoff river or storage type plants Peak load plant The hydroelectric power plant that was built only to meet the peak portion of the load curve is known as the peak load hydropower plant. The capacity of this plant is less than base load plants and these plants are turned ON only while the peak demand of load and after this plant turned OFF. Therefore, these plants are used to run for a short duration of time. In most cases, these plants are runoff river plants with pondage or storage type of hydel plant Based on the Quantity of Water Available According to the quantity of water available to generate electric power, the hydroelectric power plants are classified into five types; Run-off river plants without pondage This type of hydropower plant does not store water. It uses the water directly from the river. The power output of these plants is not constant. Because there is no control over the availability of water. Hence, the power output fluctuates and the utility of this plant is very less compared to other plants. Run-off river plants with pondage
- 12. In this type of plant, a pond is constructed behind the dam and near the plant. This pond increases the utility of the power plant. To meet fluctuating loads, the capacity of the pond decides based on the 24 hours fluctuation in load demand. This plant can be used as a base load as well as a peak load plant. Storage type plant This type of plant uses a reservoir to store water. In some areas where the water is available in rainy seasons only. In this area, the storage type of plants is used to store water in bulk amounts and use in dry seasons.The storage type of plant can be used as base load and peak load plant. The capacity of the plant decides by the water storage capacity of the reservoir. Pumped storage peak load plant This type of plant is used to meet the peak load demand. It has a reservoir to store the water. When the load demand is high, it used the water of the reservoir. And when the load demand is reduced, this plant is designed with a pump that is used to supply water from tailrace to head race. The pumped storage plants are used to run along with the steam (thermal) power plant to improve the overall efficiency of a combined power plant. The pump of this plant is energized from the secondary power plant like run-off river plant or nuclear plant. In this plant, the required water is very less compared to other hydropower plants. Mini and micro hydel plant Mini and micro hydropower plants are used to meet the power crises. Mini power plants work in the range of 5 to 20 m head and micro power plants work in the range of fewer than 5 m available water head.
- 13. This plant is a small capacity plant. and the time required and cost to build this plant are less compared to other hydroelectric plants. The mini-Hydropower Plant uses a special type of turbine known as bulb type turbine. Estimating Power Potential Technique of estimating hydropower potential Before any power plant is contemplated, it is essential to assess the inherent power available from the d is char ge of the river and the head available at the site. The gross head of any proposed scheme can be assessed by simple surveying techniques, whereas Hydrological data on rainfall and runoff are essential in order to assess the quantity of water available. The hydrological data necessary for potential assessment are: The daily, weekly, or monthly flow over a period of several years, to determine the plant capacity and estimate output, Low flows, to assess the primary, firm or dependable power. The potential or theoretical power in any river stretch with a difference in elevation H is computed from Pp = γ*Q*H Where Pp = Potential (theoretical) power of the stream in Kw H = head in m Q = stream discharge in m3/s = unit weight of water, 9.81 KN/m3 The hydraulic power P is given by P= η*γ*Q*H(KW) Where η = the total efficiency The actual use of the equation for estimating the potential, Pp, however, is made difficult due to the fact that the discharge of any river varies over a wide range. High discharges are available only for short durations in a year. The corresponding available power would be of short duration.
- 14. If the discharge rate and the percentage duration of time for which it is available are plotted, a flow duration curve results. Power duration curve can also be plotted since power is directly proportional to the discharge and available head. Dis charge/Power duration curve indicates discharge or power available in the stream for the given percentage of time. Flow duration analysis Flow duration curves A flow duration curve is a plot of flow versus the percent of time a particular flow can be expected to be exceeded A flow duration curve merely reorders the flows in order of magnitude instead of the true time ordering of flows in a flow versus time plot. The flow duration curve also allows the characterizing of the flow over long periods of time to be presented in one compact curve. Characteristics of Flow Duration Curves The flow duration curve (FDC) shows how flow is distributed over a period (usually a year). A steep flow duration curve implies a flashy catchment – one which is subject to extreme floods and droughts Factors which cause a catchment to be flashy are Rocky, shallow soil Lack of vegetation cover, Steep, short streams, Uneven rainfall (frequent storms, long dry periods). Such type of FDC (i.e. steep) is bad for hydropower development (especially run- of-river type). A flat flow duration curve is good because it means that the total annual flow will be spread more evenly over the year, giving a useful flow for longer periods, and less severe floods. Characteristics of a flat FDC are: Deep soil, Heavy vegetation (e.g. jungle), Long gently sloping streams, Bogs, marshes, Even rainfall (e.g. temperate climate).
- 15. Power Duration Curve Minimum potential power computed from the minimum flow available for 100 % of the time (365 days or 8760 hours). This is represented as Pp100; Small potential power computed from the flow available for 95 % of time (flow available for 8322 hours). This is represented as Pp95; Average potential power computed from the flow available for 50% of the time (flow available for 6 months or 4380 hours). This is represented as Pp50; Mean potential power computed from the average of mean yearly flows for a period of 10 to 30 years, which is equal to the area of the flow-duration curve corresponding to this mean year. This is known as ‘ Gross river power potential’ and is represented as Ppm. It would be more significant to find out the technically available power from the potential power;