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Impulse turbine
- 1. IMPULSE TURBINE • MadeBy:-Amrit Raj(sg14907) • Anil Kumar(sg14908) • Ankit Dev singh(sg14909) • Ankit Sherawat(sg14910)
- 2. DEFINITION OF TURBINE A Turbine is a Form of Engine Requires a suitable working fluid in order to function- a source of High Grade Energy and a Sink for Low Grade energy. When a Fluid Flows through the Turbine ,Part of Energy Content is Continuously Extracted andConverted in to Useful mechanical Work. • A turbine converts energy in the form of falling water into rotating shaft power. The selection of the best turbine for any particular hydro site depends on the site characteristics, the dominant ones being the head and flow available. Selection also depends on the desired running speed of the generator or other device loading the turbine. Other considerations such as whether the turbine is expected to produce power under part-flow conditions, also play an important role in the selection. All turbines have a power-speed characteristic. They will tend to run most efficiently at a particular speed, head and flow combination.
- 3. WORKING PRINCIPLE OF IMPULSETURBINE The steam is made to fall in its pressure by expanding in a nozzle. Due to this fall in pressure, a certain amount of heat energy is converted into kinetic energy, which sets the steam to flow with a greater velocity. The rapidly moving particles of the steam enter the rotating part of the turbine, where it undergoes a change in the direction of motion, which gives rise to a change of momentum and therefore force. This constitutes the driving force of the turbine.
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- 5. PELTON TURBINES • Theonly type of impulse turbine that is in use these days is Pelton turbine. It is also called a free jet turbine as it uses a free jet of water under atmospheric pressure. • It works under high head and uses less quantity of water. Water from the reservoir is brought to the turbine through penstocks, at the end of which a nozzle is fitted. The nozzle converts whole of the available head into the kinetic head in the form of a high velocity jet.
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- 7. PELTON TURBINES • Thejet strikes the buckets mounted on the rim of a wheel called runner. • A shaft passes through the runner. The force of jet causes the runner to rotate and mechanical power is produced. • In the end water goes into the tail race. • Number of nozzles depends upon specific speed. However, maximum number of nozzles can be 6.
- 8. COMPONENTS OF APELTON TURBINE Runner with Buckets • The runner of a Pelton turbine consists of a number of double cupped buckets fixed to the periphery of the wheel. • Each bucket has a sharp edge at the center called the splitter • The jet strikes each bucket at this splitter and is divided into two sides, thus avoiding any unbalanced thrust on the shaft. • As the splitter takes the full impact of the jet, so it has to be quite strong.
- 9. COMPONENTS OF APELTON TURBINE Runner with Buckets
- 10. COMPONENTS OF APELTON TURBINE Nozzle with guide mechanism • The function of the nozzle of a Pelton wheel is to convert the available pressure energy into high velocity energy in the form of jet. • The quantity of water required is proportional to the load on the turbine. Therefore, to control the flow through the nozzle, some sort of a regulating or a governing mechanism is necessary. This is generally done by using a spear inside the nozzle. The movement of spear inside the nozzle changes the area of flow through it, thus varying the discharge.
- 11. COMPONENTS OF APELTON TURBINE Nozzle with guide mechanism • The nozzle is usually made of either cast iron or cast steel. • Sometimes, a small brake nozzle is also used in case of large turbine When the wheel is to stopped, besides cutting off the supply of wate through the main nozzle, the brake nozzle also directs the water on to th back of buckets to bring the wheel quickly to rest.
- 12. COMPONENTS OF APELTON TURBINE Casing • The casing is not to perform any hydraulic function. • However, a casing is necessary to avoid accidents, splashing of water, to lead the water to the tailrace and to support the hosing for the bearing and the nozzle. • Material for the casing is usually cast iron.
- 13. DIMENSIONS OF BUCKET Theminimum possible width B of the bucket is approximately 2d, where d is the diameter of jet. This dimension is usually taken as 2.8 to 3.2d to avoid losses. Some prefer to take it as 3 to 4d. The depth of the bucket (T) usually lies between 0.8 to 1.2d. The height (H) of the bucket is 2.4 to 2.8d. Other dimensions of the bucket are taken as below: E = 1.2d F = 0.4d G = 0.9 to 1.0d βi = 3 – 6 degrees βo = 10 - 20 degrees
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- 15. NUMBER OF BUCKETS Thenumber of buckets is decided such that the frictional loss is minimum and the path of the jet is not disturbed and the jet must be fully utilised, i.e. all the water particles strike the buckets and impart kinetic energy to the wheel. Taygun gave the following relation for the calculation of number of buckets. where m = D/d = Jet Ratio D=dia. of runner, d=least dia. of the jet 155.015 2 1 +=+= m d D bn
- 16. DIAMETER OF JET •The velocity of jet out of a nozzle is given by, where, Vi = Velocity of jet Cv = Coefficient of velocity for the nozzle; value lies between 0.96 – 0.99 d = diameter of the jet Discharge through the nozzle, gHCV vi 2= gHCdVdQ vi 2. 4 . 4 22 ππ == gHC Q d v 2 4 π =
- 17. SPEED RATIO Speed ratio(Ku) of a Pelton turbine is defined as the ratio of the tangential ve of wheel u to the theoretical velocity of the jet. where in which N is the speed in rpm gH u Ku 2 = 60 DN u π =
- 18. JET RATIO • Jetratio is defined as the ratio of the diameter of runner to the least diameter of jet, d D m =
- 19. NUMBER OF JETS •Number of jets may be increased, usually upto 4, but never more than 6 because higher number of jets makes the governing complicated.
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