2.1 INTRODUCTION OF HYDRO POWER PLANT Theory and working: The purpose of hydro electric plant is to provide from water flowing under pressure. Water flowing under pressure has two forms of energy kinetic and potential. Kinetic energy depends upon the mass velocity of flow while the potential energy exists as a result of difference in water level below the points of the turbine connects potential energy & kinetic energy possessed by water into mechanical power. Thus the turbine is a prime mover which can be coupled to generator producers. Details of hydro power plant are shown in Fig. 2.1. Fig 2.1 Hydro power plant Electric power: Hydro electric power can be developed when water continuously flowing under pressure is available. Dam is constructed to redirect the river water flow. Essential components of a hydro electric power plant are as follows: Storage reservoir: The water available from an attachment area is stored in a reservoir so that it can be run to utilize the turbine for producing power according to requirement. Dam with control work: Dam is a structure ejected on a suitable site to provide for the storage of the water and created head. Dam may be built to make an artificial reservoir from the valley or it may be created in a river to control the flowing water. Water ways: Water ways is a passage through the water carried from the storage reservoir to the power houses. It consists of tunnel control, force pipe and penstock. Tunnel is a water passage made by cutting to mountain to save distance for bay in an enlarged section canal spread to accommodate the required width of Intake its function is to store temporarily water rejected to plant. Penstock: It is a pipe of large diameter carrying water under pressure from storage top tank. Power house: It is a building to house the turbine penstock and others for operating the machines. Spill way: It is a safety valve for dam. Water after a certain level in the reservoir overflows through spill way without allowing the increase in water level in the reservoir particularly during rainy season. Surge tank: This helps in reducing the pressure surges developed due to sudden back flow of water as load on the turbine it reduced. Otherwise penstock will be damaged by the water hammer produced by sudden back flow. Prime mover: It converts the potential energy of water to the mechanical energy. Head race: Water surface of reservoir level is called head race. Tail race: Water passing through turbine is discharged through tail race. Fig 2.2 Turbine generator 2.2 CLASSIFICATION OF HYDRO POWER PIANT The hydro power plant can be classified according to the following four categories. 2.2.1 On the basis of availability of water and site (a) Run off river power station without pondage. (b) Reservoir power station. 2.2.2 Classification based on plant capacity (a) Micro hydel - less than 5mw (b) Medium capacity - -5 - 100mw (c) High capacity - 101 – 1000 mw (d) Super plants - more than >1000 mw 2.2.3 Depending on the load (a) Base load power plants (b) Peak load power plants 2.2.4 On the basis of available head (a) High head - more than 180 m head (b) Medium head - between 30 – 180 m head (c) Low head - less than 30 m head. 2.3 HYDRO TURBINE Hydro turbine is the machine which is used to convert the energy of water into mechanical energy, and mechanical energy developed by the turbine is used to run the electric generator which is directly coupled with the shaft of turbine. Turbine consists of wheel called runner, having the number of blades or buckets. 2.3.1 Classification of hydro turbines Hydro turbines can be classified as under: (1)On the basis of head and the quantity of water available (a) Impulse turbine - above 200 m -> high head and low flow rate (b) Francis turbine -between 30 m to 180 m head (medium head) and medium flow rate (c) Kaplan turbine -Low head and high flow rate -> head below the 30 m (2) On the basis of name of originator (a) Pelton turbine - named in honour of allen pelton (1829 - 1908) of California (USA), is an impulse type of turbine used for high head and low discharge. (b) Francis turbine: - named after James Bichens Francis (1815 - 1892) who was born is England and later went to USA, is a reaction type of turbine for medium high to medium low heads and medium small to medium large quantities of water. (c) Kaplan turbine - named in honour of Victor Kaplan( 1878 - 1934) of Bruenn (Germany) is a reaction type of turbine for low heads and large blades. (3) On the basis of direction of flow of water in the runner: In tangential flow turbine of pelton type, the water strikes the runner tangential to the path of rotation. This path is the centre line of buckets which is, sometimes, known as pitch circle diameter or mean dia. of wheel. In radial turbine, water enters radially and emerges out so that the discharge is parallel to the axis of the shaft. Modern Francis turbines have mixed flow runners. In axial flow turbine, water flows parallel to the turbine shaft. In inward flow turbine, the water flows from the periphery towards centre of the wheel. (4) On the basis of disposition of turbine shaft Turbine shaft may be either vertical or horizontal. In modern turbine practice, Pelton turbines usually have horizontal shaft whereas the rest, specially the large units, have vertical shaft. (6) On the basis of specific speed. Specific speed 10 -20 - Slow pelton runner Turbine 20 – 30 - medium pelton turbine Pelton turbine 30 – 35 - fast pelton runner 35 – 60 - Multi jet pelton runner Francis turbine 60 – 120 - Slow Francis runner 120 – 180 - Medium Francis runner 180 – 300 - Fast Francis runner Kaplan 300 – 1000 - Kaplan. 2.4 IMPULSE AND REACTION TURBINES: (a) Impulse turbine: The water is brought in through the penstock end into single nozzle. The whole pressure energy of water is converted into kinetic energy. The water coming out of the nozzle in the form of a free jet is made strike on a series of buckets mounted on the periphery of a wheel. The water delivered to the wheel on a part of its circumference filling or striking only few of the buckets at the time. The wheel revolves in open air, there is no pressure difference in water at the inlet to the runner and the discharge therefore the casing of an impulse turbine has no hydraulic function to perform. It is necessary only to prevent splashing and to load the water to the race and also acts as a safeguard against accidents. This turbine is also known as a free jet turbine. In such type of turbine P1 = P2 ; V1>>>V2 Vr1 Vr2 (Neglecting the losses in buckets) (b) Reaction turbine: The reaction turbine operates with its when submerged in water. The water before entering the turbine has pressure as well as kinetic energy. All pressure energy is not transformed into kinetic energy as in case of impulse turbine. The moment on the wheel is produced by both kinetic and pressure energies. The water leaving the turbine has still some of the pressure as well as the kinetic energy. The pressure at the inlet to the turbine is much higher than the pressure at the outlet thus there is a possibility of water flowing through some passage other than the runner and escape without doing any work. Hence a casing is absolutely essential due to the difference of pressure in reaction turbine. For this type of turbine P1>>P2 ; V1 > V2 and Vr1 <Vr2 2.5 HEADS OF A TURBINE (1) Cross head: The difference between the head race level and tail race level when no water is flowing is known as cross head It is denoted by Hg. Net head: It is also called effective head and is defined as the head available at the inlet of the turbine. When water is flowing from head race to the turbine, a loss of head due to friction between the water and penstock occurs. There are losses due to bend, pipe, fitting, loss at entrance of pen stock etc. Suppose frictional losses are hf between penstock and turbine. so Net head (H) = Gross head (Hg) + hf(friction head loss) hf is calculated by hf hf where D = dia of penstock. L =length of penstock V= velocity of water. 2.6 CONSTRUCTION DETAILS OF PELTON TURBINE: Theory: This is the only turbine that it in common use, named in the honour of Mr. L.A. Pelton (1829 - 1908) of California, U.S.A. Who contributed much to its development and got it patented m 1889. It is an efficient turbine particularly suited to high heads and therefore required a comparatively less quantity of water. Pelton turbine is an impulse turbine which is used to utilize high head for generation of power by converting it into kinetic energy by means of a spear and nozzle arrangement. The water leaves the nozzle in the form of jet, then strikes the bucket of the turbine. After striking the bucket the jet of water is deflected through an angle of 16- and 170 degree. While passing over the bucket the velocity of water is reduced and hence an impulsive force is supplied to them which is turn start rotating. The water impinging on the bucket of a Pelton turbine is shown in Fig 2.3. Fig 2.3 Construction detail The main components of a Pelton Turbine are: (a) Penstock: It is a large size conduit with conveys water from the higher level reservoir turbine, depending upon low head or the high head installations.