Definition of A Turbo Machine

1. Definition of A Turbo Machine • Turbines are energy developing machines. Turbines convert fluid energy into mechanical energy. The mechanical energy developed by the turbines is used in running an electric generator, which is directly connected, to the shaft of the electrical generator. • Earlier days method – wooden wheel • Overshot Wheel • Had very good efficiency • Could not handle large quantity of water • Undershot Wheel • Low Efficiency

2. General layout of Hydro-Power Plant a)  Reservoir Reservoirs ensure supply of water through out the year, by storing water during rainy season and supplying the same during dry season. b)  Dam The function of the dam is to increase the reservoir capacity and to increase the working head of the turbine. c) Penstock A pipe between dam and turbine is known as penstock. It will carry the water from dam to turbine. Penstock is commonly made of steel pipes covered with RCC.

3. d)  Surge tank/Forebay When the rate of water flow through the penstock is suddenly decreased, the pressure inside the penstock will increase suddenly due to water hammer and thereby damage the penstock. Surge tank/Forebay is constructed between the dam and turbine. It will act as a pressure regulator during variable loads. e)  Turbine Turbines convert the kinetic and potential energy of water into mechanical energy to produce electric power. f) Generator and Transformer Electric generator converts mechanical energy into electrical energy. A step up transformer will increase the voltage for loss free transmission.

4. General layout of Hydro-Power Plant

5. Advantages and Disadvantages of HPP • Advantages of hydraulic power plants • Operating cost is very low • Less Maintenance cost and less manpower required • Pollution free • Quick to start and easy to synchronize • Can be used for irrigation and flood control • Long plant life. • Disadvantages of Hydraulic Power Plants • Initial cost of total plant is comparatively high • Power generation depends on availability of water • Cost of transmission is high since most of the plants are in remote areas • Project duration is long.

6. Head of Hydraulic Turbines • 1) Gross Head • Difference Between the Head race level and Tail race level • Static (No water flow) / Total Head – H1 • 2) Net or Effective Head • Head available at the entrance of the turbine: H = H1 - hf • a) Net Head for a Reaction Turbine • H = {(P1/w) + (V12/2g) + Z1} – {Z2 + V22/2g)} • b) Net Head for Impulse Turbine • H = {(P1/w) + (V12/2g) + Z1} – Z2

7. Efficiencies of Hydraulic Turbines • Hydraulic Efficiency – due to hydraulic losses • Power developed by the runner • Net power supplied at the turbine entrance • SI Unit: kW • Metric Unit : Horse Power/Water Horse Power (W.H.P) • 2) Mechanical Efficiency – Due to mechanical losses ( bearing friction) • Power available at the turbine shaft (P) • Power developed by the runner

8. Cont… • 3) Volumetric Efficiency – due to amt of water slips directly to the tail race • Amount of water striking the runner • Amount of water supplied to the turbine • 4) Overall Efficiency • Power available at the turbine shaft (P) • Net power supplied at the turbine entrance

9. Classification of Turbines Turbines are classified according to several considerations as indicated below. i)   Based on working principle a)  Impulse turbine b)  Reaction turbine

10. Cont… Impulse Turbine: The pressure of liquid does not change while flowing through the rotor of the machine. In Impulse Turbines pressure change occur only in the nozzles of the machine. One such example of impulse turbine is Pelton Wheel. Reaction Turbine: The pressure of liquid changes while it flows through the rotor of the machine. The change in fluid velocity and reduction in its pressure causes a reaction on the turbine blades; this is where from the name Reaction Turbine may have been derived. Francis and Kaplan Turbines fall in the category of Reaction Turbines.

11. Cont… ii)    Based on working media a)  Hydraulic turbine b)  Steam turbine c)  Gas turbine d)  Wind Turbine iii)   Based on head Head is the elevation difference of reservoir water level and D/S water level. a)  High head turbine (Above 250 m) Pelton Turbine b)  Medium head turbine (60 – 250 m) Francis Turbine c)  Low head turbine (Below 60 m) Kaplan Turbine

12. Cont… iv)   Based on specific speed Turbines can be classified based on Specific Speed. Specific speed is defined as the speed in rpm of a geometrically similar turbine, which is identical in shape, dimensions, blade angles and gate openings with the actual turbine working under unit head and developing unit power. Specific speed is used to compare the turbines and is denoted by Ns. Specific speed  Ns =  N √P / H5/4 a)  Low specific speed (8.5 – 30) - Pelton Turbine b)  Medium specific speed (50 – 340) - Francis Turbine c)  High specific speed (255 – 860) - Kaplan Turbine

13. Cont… v)   Based on disposition of turbine main shaft a)  Horizontal shaft b)  Vertical shaft vi)  Based on flow through the runner a)  Radial flow 1. Inward 2.  Outward b)  Axial flow - Kaplan Turbine c)  Mixed flow - Francis Turbine d)  Tangential flow - Pelton Turbine

14. Pelton Wheel Turbine Design of Pelton Wheel Turbine • It has a circular disk with cup shaped blades/buckets, • Water jet emerging from a nozzle is tangential to the circumference of the wheel.

15. Working Principle of Pelton Turbine • Water jets emerging strike the buckets at splitter. • Stream flow along the inner curve of the bucket and leave it in the direction opposite to that of incoming jet. • The high pressure water can be obtained from any water body situated at some height or streams of water flowing down the hills. • The change in momentum (direction as well as speed) of water stream produces an impulse on the blades of the wheel of Pelton Turbine. This impulse generates the torque and rotation in the shaft of Pelton Turbine. • Horizontal shaft - Not more than 2 jets are used and Vertical shaft - Larger no. of jets (upto 6) are used. • Iron/Steel casing to prevent splashing of water and to lead water to the tail race.