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Note for Power Plant Engineering - PPE By UPTU Risers

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Ccccc POWER PLANT ENGINEERING (REE-401) UNIT-I Unit-I: Hydro-electric power plants- selection of site, elements of power plant, classification, water turbines, governor action, hydro-electric generator, plant layout, pumped storage plants. 1.1INTRODUCTION: Hydro-electric power plants uses the kinetic or potential energy of water to produce electrical energy by electromechanical energy conversion phenomenon. The motion of water provides it kinetic energy while potential energy is there due to the different levels of water between two points, called head. In both the cases water is collection is necessary which is to be done by collecting it in lakes and reservoirs at high altitudes which may be natural or manmade constructions like artificial lake, ponds or dams. A hydro power station may be solve several problems like, power generation, comprising flood control, irrigation etc. A hydroelectric power station cannot be located anywhere. The requirments to stablish it is more specific. Fristly there must be ample quantity of water available at sufficient head and secondly a suitable site must be there. It requires an effective civil engineering work, a hudge construction and a big capital cost. 1.2 WATER POWER: Water storage has potential energy. When water drops through a height, its energy is able to rotate turbines which are coupled with alternators. By electromechanical conversion action this energy is converted into electrical energy. From Bernoulli’s equation, the electrical power , P is given 0.736 Pο€½ Qwh kW by: 75 where: Q = discharge in m3/sec w = density of water = 1000 kg/m3 h = head in meters. Another way is to represent this power is as: 0.736 Pο€½ Qwh  kW; 75 (πœ‚=overall efficiency of turbine alternator set). 1.3 SITE SELECTION: Following factors should be considered while selecting the site of a hydro power plant: (i) Availability of Water: The river run-off data pertaining to many previous years should be analyzed to estimate of the power potential of the project can be done. It decides the capacity of the plant. Also useful to setting up of peak load and avoid adequate spillways relief during the flood periods. (ii) Water Storage: Water storage is necessary to maintain the availability of water throughout the year which may affected by the wide variation in rainfall during the year. (iii) Head of Water: In order to generate power, proper head of water is very important. An increase in head of water reduces the capital cost of the plant by reducing the storage of water, handled by penstock, screens and turbines. (iv) Distance from the load centre: The site should not locate far away from the load centre because this may increase the cost of transmission line and the losses By: DEEPAK PANDEY associated with it. (v) Access to site: The site should be easily accessible and it should have transportation facilities. (vi) Geological investigations: Geological survey is very important to see the foundation rock for the dam and other structures. It is an important factor to understand that the land where we are going to construct hydro plant is capable to withstand the stress of such mega structures. 1.4 ADVANTAGES: (i) No fuel is required, therefore operating cost is low. (ii) Large life span (about 50+ years). (iii) No standby losses. (iv) These plants are more robust as compared to others. (v) Maintenance cost is low as compared to steam and nuclear power plants. (vi) Efficiency does not depend on its age. (vii) Its use helps in conservation of fossil fuels. (viii) Few skilled workers are required to run the plant. (ix) In addition to power generation, multiple projects like irrigation, flood control, navigation etc. are also served at same time. (x) Free from air pollution. 1.5 DISADVANTAGES: (i) High capital cost. (ii) These plants are dependent on water availability, so in a dry year, the power generation is very small. (iii) Required large time to build. (iv) Proper supervision of dam is required. 1.6 CLASSIFICATION OF HYDRO-ELECTRIC POWER PLANT: The classification of hydro-electric power plant is based on: (1) Quantity of water available (2) Available load (3) Nature of the load (1) Quantity of water available: According to this the plants may be divided into: (a) Run-off River plants without pondage (b) Run-off River plants with pondage (c) Reservoir plants. (a) Run-off River Plants Without Pondage: οƒ˜ The plant uses water as it comes, there is no storage or pondage. οƒ˜ There is no control on flow of water. So during periods of high flows or low loads, water is wasted while during lean flow periods, the plant capacity is very low. οƒ˜ Such sites are mainly used for irrigation or navigation whereas the plant is only identical. (b) Run-off River Plants With Pondage: οƒ˜ In such sites pondage are used for storing the water email: d.pandey2906@gmail.com Page 1

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which permits storage of water during the peak-off periods and use it during peak-off load. οƒ˜ The firm capacity of the plant increases. οƒ˜ This type of plant is more reliable and its generating capacity is less dependent on available rate of flow of water. DAM HEAD RACE SURGE TANK POWER HOUSE C O ST N PE (c) Reservoir plants: οƒ˜ These plants have a reservoir of such size as to permit water storage from wet season to the next dry season. οƒ˜ Water is stored behind the dam and is available to the plant with control as required. οƒ˜ These plants having better capacity and works efficiently throughout the year. οƒ˜ Most of the hydro power plants belong to this category. (c) High Head Plants: οƒ˜ Head is above 300 mtrs. οƒ˜ In such plants, all water is carried from the main reservoir by a tunnel upto a surge tank and then to the power house in penstock. οƒ˜ For lower head Francis turbine is common but heads above 500 meters. Pelton turbines are used. HEAD RACE DAM POWER HOUSE TAIL RACE A Low Head Plant (b) Medium Head Plants: οƒ˜ In medium head plants, the water head is between 30 to 300 mtrs. οƒ˜ Water is generally carried in open canals from main reservoir to the fore-bay and then to the power house through the penstock. οƒ˜ Generally Francis, Propeller and Kaplan turbines are used. HEAD RACE TAIL RACE FOREBAY A High Head Plant (3) Nature Of The Load: On basis of nature of the load, plants may be divided as: (a) Base-load Plants, (b) Peak-load Plants, (c) Pumped storage plants for peak-loads. (a) Base Load Plants: οƒ˜ They are used to provide base load to the system. οƒ˜ Generally of high efficiency. οƒ˜ Supplies almost constant load throughout. οƒ˜ Operate on a high load factor. οƒ˜ Run-off river plants without pondage and reservoir plants can be used as base load plants. (b) Peak-load Plants: οƒ˜ They are use to supply peak loads to the system. οƒ˜ Run-off river plants with pondage can be used as peakload plants. οƒ˜ Reservoir plants with enough storage can be used either as base-load plants or as peak-load plants as required. (c) Pumped Storage Plants For Peak-loads: HEAD RACE D A M PENSTOCK HEAD (a) Low Head Plants: οƒ˜ In such plants the water head is less than 30 mtrs. οƒ˜ Small dam is built across the river to provide the necessary load. οƒ˜ In such plants no surge tank is needed. οƒ˜ The excess water is allowed to flow over the dam itself. οƒ˜ Francis of Kaplan turbines are used. TAIL RACE K (2) Available Head: Hydro power plants may be classified as: (a) Low Head Plants, (b) Medium Head Plants, (c) High Head Plants. POWER HOUSE WITH PUMPS TAIL RACE PENSTOCK POWER HOUSE A Medium Head Plant Pumped Storage Hydro Electric Plant By: DEEPAK PANDEY email: d.pandey2906@gmail.com Page 2

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οƒ˜ They are used when the availability of water quantity is insufficient for generation. οƒ˜ A storage pond is built to store water at head and tail race. οƒ˜ Head race water is fed to the turbine to generate electrical energy and this water is stored in tail race which may be again pumped up to the head race when required through a centrifugal pump. οƒ˜ The pumping back of water is done during off-peak period. οƒ˜ Such plants can only be operated in interconnected systems where other generating plants are also available. 1.7 LAYOUT OF A HYDRO-ELECTRIC POWER STATION: Figure shows a general layout of a hydro electric power plant with an artificial storage reservoir formed by constructing dam across a river. Water from the storage reservoir is carried through penstocks or canals to the power house. This water is used to rotate the turbine and after passing through the turbines this water is discharged to the tail race. The tail race is the channel which carries water away from the power house after it has passed through the turbine. ENERGY LINE GROSS HEAD DAM PENSTOCK GENERATOR REACTION TUBE TAIL RACE DRAFT TUBE (a) DAM GROSS HEAD IMPULSE TURBINE PENSTOCK NOZZLE TAIL RACE (b) General layout of a hydro-electric power plant. 1.8DIFFERENT COMPONENTS IN HYDROELECTRIC PLANT: The following are the main components/stages of a hydroelectric plant: (a) RESERVOIR: Its purpose is to store water which may be utilized to run the prime mover of the turbine to produce electrical energy. A reservoir stores water during rainy season and delivers it during the dry season. (b) DAM: It provides a head to the water to be utilized in the water turbine, which can be used throughout the By: DEEPAK PANDEY year by proper controls. (c) TRASH RACK: It prevents the entries of debris which might damage the wicket gates and turbine runners of mean choking of nozzles of the turbine. It is made of steel bars and is placed across the intake. (d) FOREBAY: It works as a regulating reservoir storing water temporarily when load on the plant is reduced and providing water for increasing load situation. It is and enlarged body of water at the intake to store water temporarily to meet the hourly load fluctuations. It may email: d.pandey2906@gmail.com Page 3

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be enlarged section of the canal or a pond. (e) SURGE TANK: This is an additional storage space near the turbine, generally used in high head and medium head plants when there is a considerable distance between the water source and turbine which necessitates a long penstock. When the load on the turbine decreases the surge tank provides space for holding water. Similarly when load on the turbine increases it furnished additional water. (f) PENSTOCK: It provides a path for taking water from the intake work and fore-bay to the turbines. Penstocks may be classified as, the low pressure and high pressure. (g) SPILLWAY: Spillway is an arrangement to discharge excess water during floods. These should be so designed as to discharge the major flood water without damage to the dam but the same time maintain a predetermined head. (h) POWER HOUSE: Power house is generally located at the foot of the dam and near the storage reservoir and responsible for power generation. (i) PRIME MOVER: They are used to convert the kinetic energy of the water into mechanical energy. Commonly used prime movers are Pelton wheel, Francis/Kaplan/Propeller turbines. (j) TAIL RACE: It is required to discharge the water, leaving the turbine, into the river. an impulse turbine are usually bucket-shaped so they catch the fluid and direct it off at an angle or sometimes even back the way it came (because that gives the most efficient transfer of energy from the fluid to the turbine). In an impulse turbine, the fluid is forced to hit the turbine at high speed. (b) REACTION TURBINES: In a reaction turbine, the blades sit in a much larger volume of fluid and turn around as the fluid flows past them. A reaction turbine doesn't change the direction of the fluid flow as drastically as an impulse turbine: it simply spins as the fluid pushes through and past its blades. Wind turbines are perhaps the most familiar examples of reaction turbines. (i) PELTON TURBINE: HO R CASING T BU E CK IZ SH ONT AF AL T GRADIENT SPEAR RESERVOIR DAM SURGE TANK TUN N POWER HOUSE EL PENSTOCK Surge Tank & Pen Stock 1.8 HYDRAULIC TURBINES: According to their action, the hydraulic turbines may be divided into two categories: (a) Impulse turbines; (b) Reaction turbines. (a) Impulse Turbine (b) Reaction Turbine (a) IMPULSE TURBINES: In an impulse turbine, a fast-moving fluid is fired through a narrow nozzle at the turbine blades to make them spin around. The blades of By: DEEPAK PANDEY WATER JET TAIL RACE WATER FROM PENSTOCK Pelton Turbine οƒ˜ This turbine work under large head and low quantity of water. οƒ˜ It is tangential flow impulse turbine. οƒ˜ The pressure inside is atmospheric pressure, in which the potential energy of water in the penstock is converted into kinetic energy in a jet of water issuing from nozzle. οƒ˜ From the nozzle, water comes out in the form of jet and strikes the buckets of the runner and causes the motion of the rotor. οƒ˜ After performing work, water discharges into tail race. οƒ˜ The rate of flow of water can be controlled by the movement of spear. οƒ˜ The rotor (or runner) is made of cast steel. οƒ˜ The buckets are bolted on the runner and made of cast iron, bronze or stainless steel. οƒ˜ For low head of water, Pelton wheel required a large diameter for the same output so it is not suitable for heads below 200 m. email: d.pandey2906@gmail.com Page 4

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