HYDRAULIC TURBINES GATE MASTER S ACADEMY. Hydraulic turbines

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1 8 YDRAULIC TURBIES 0. Ans : (a & d) ydraulic machine is a device which converts fluid energy into mechanical energy is called turbine. ydraulic machine is a device which converts mechanical energy into fluid energy is called pump. 0. Ans : (a) Turbine : It is machine for producing continuous power in which a wheel (or) rotor fitted with vanes (blades), is made to revolve by a flow of moving fluid (i.e. water, steam, gas, air (or) other fluid of working substance). ence a turbine is a machine that transforms rotational energy from a fluid is picked up by a rotor into usable energy (or) work. Ex : Water turbines, steam turbines, Gas turbines, wind mill etc. Water (or) hydraulic turbine 03. Ans : (c) ydraulic turbine (or) Water turbine : It is a rotary machine that converts hydraulic energy (potential and kinetic energy) of water into mechanical energy (or) work. Ex : Impulse turbines (elton wheel Turgo, Banki). Reaction turbines (Francis, Kaplan and ropeller turbine). ote : i) Electric generator : It converts mechanical energy into electrical energy. ii) ydraulic energy means potential energy ( or) kinetic energy (or) combination of both. iii) ump is also a hydraulic machine which converts mechanical energy into hydraulic energy. 06. Ans : (a) ump is a mechanical device that moves fluids (liquids (or) gases) by mechanical action. ump consume mechanical energy (by means of electric motor, heat engines, wind power ( or) manual), operates by rotary (or) reciprocating mechanism. S.o. ame of machine (or) device Function ump Mechanical energy into hydraulic energy ydraulic Turbine ydraulic energy into mechanical energy 3 Electric motor Electrical energy into mechanical energy 4 Electric generator Mechanical energy into electrical energy 8. Ans : (d) Methods of avoid cavitation in reaction turbines :. Special materials (or) coatings such as aluminium-bronze and strainless steel, which are cavitation resistant materials should be used.. Install reaction turbine below the tail race water level. 3. rovide blades with smooth surfaces 4. ressure of flowing liquid in any part of the turbine should not be allowed to fall below the vapour pressure. Ex : For water flow in turbine, absolute pressure head should not be below.5 m of water. 0. Ans : (c) enstock is the long pipe that carries the water flowing from the reservoir towards the power generation unit. The water in penstock possesses kinetic energy due to its motion and potential energy due to height. It transports water under pressure forebay to turbines.. Ans : (d) enstock is a high pressure steel pipe line that carries water from storage reservoir to the turbine. Steel material is sued for the following Reasons: Limited water hammer effect durability, easy joining / fabrication/ weld methods; pressure ( static &

2 dynamic) of passing water limitations since penstocks are required to withstand high pressure because of high heads. Steel penstock pipes withstands hydrodynamic pressure (Water hammer pressure). Steel provides more strength against bursting of pipe under dynamic pressure.. Ans : (d) Surge tank : It is a hydraulic structure used to control pressure and flow fluctuations in a penstock. Functions : It Reduces water flow transient pressures in penstock (i.e. reduces water hammer effect). 4. Ans : (c) Surge tank connected to penstock before turbine for the follows :. To reduce water hammer for penstock pipe U/S of flow control value.. acts as storage of water 3. Absorb oscillations etc. 6. Ans : (b) Surge tank in a penstock pipe should be provided to relieve the dynamic pressure due to water hammer influence. It should be located as close to the turbine. 7. Ans : (d) Tailrace : The water from penstock pass through turbine, draft tube and has to pass itno main river stream through tail race. 9. Ans : (c) Susceptible part of a water turbine to cavitation is (i) at exit of reaction turbine (ii) at inlet of the draft tube 0. Ans : (a) Gross ead : Difference in vertical height between the water intake and tailrace levels. The difference in elevation between the free water surface of dam above and tail water surface below a hydel power plant (i.e. head race and tail race). Ans : (d) Effective head (or) et head : It is the head available at the inlet of the turbine. et head Gross head ead loss due to friction. g h f 8. Ans : (c) Tangential flow elton wheel Radial flow Francis Axial fow Kaplan turbine Mixed flow Modern Francis 30. Ans : (c) Cavitation is observed in reaction turbines like Francis turbine, Kaplan turbine, propeller turbine and centrifugal pumps. Cavitation is not occur in Impulse turbine (elton wheel) and reciprocating pump. 3. Ans : (b) Avoiding cavitation in reaction turbines:. Turbine parameters should be set such that at any point of flow static pressure may not fall below the vapour pressure of the liquid.. Flow separation at exit of turbine in the draft tube entrance causes vibrations. To stabilize this, inject air in the draft tube. Draft tube is to be submerged below the level of the water in tailrace 33. Ans : (d) Impulse turbine : (Ex : elton wheel, Turgo, Banki turbines) It is classified based on type of energy of water at inlet, direction of flow, head available, specific speed range etc. i. Initially water from reservoir (.E), fully converted into kinetic energy at end of nozzle (i.e. Impulse action) ii. Flow is tangential iii. igh head of water required

3 iv. Works in open atmosphere (o pressure change according to turbine). v. During flow across the pelton wheel, there is change in velocity only. vi. It works on Impulse-momentum principle (i.e. impact of jet causes force exertion). vii.elton wheel is a tangential flow impulse turbine. viii. Turgo wheel is an axial flow impulse turbine ix. Banki turbine is a radial flow impulse turbine x. Jonval turbine is an axial flow type impulse turbine. 46. Ans : (b) Cavitation occurs when the static pressure of the liquid falls below its vapour pressure of that liquid. 47. Ans : (b) Force exerted by a water jet on a bucket of pelton wheel (or) series of vanes mounted on fixed axis wheel is determined by "Impulse-momentum" rinciple. 48. Ans : (c) Casing has no hydraulic function. In impulse turbines, it is necessary to prevent the splashing of water to lead the water towards tail race and to safeguard against any accident. It is made strong enough to resist reaction of jet. ote : To convert.e to K.E, nozzle is used. 49. Ans : (c) Cv g m Approximate answer is 'C' 50. Ans : (a) Speed ratio () of pelton wheel varies from 0.4 to 0.5 ractical range of is 0.44 to 0.46 S.o. Turbine Speed ratio Flow ratio elton wheel 0.4 to Francis 0.6 to Turbine Kaplan & 3. ropeller.8 to turbine 5. Ans : (a) U D/60 g g D 50/ D 0.95 m 53. Ans : (d) JET RATIO : It is defined as the ratio of the pitch diameter (D) of the pelton wheel to the diameter of the jet (d). It is denoted by "m" D m d The range of jet ratio: 0 to Ans : (c) o. of buckets on the periphery of a pelton wheel (or) on a runner is given by D Z 5 0.5m 5 d [Tygun's emperical formula] Gibson's formula (Z) constant m When constants are between 7 to 8 Jet ratio (m) is between 0 to 0 3

4 58. Ans : (d) m 4 Z Ans : (b) In practice, the number of nozzles provided is generally not allowed to exceed six. 60. Ans : (b) Force on the pelton wheel bucket is obtained by using impulse momentum equation 6. Ans : (b) Breaking jet in a pelton wheel : To stop the runner of a pelton wheel in a short interval of time, a small nozzle is provided, which directs the jet on the back of the buckets. This jet of water is called breaking jet. 6. Ans : (b) Breaking jet is used in pelton wheel to reduce the speed of the wheel (or) bring the runner to rest in short time. 63. Ans : (b) Dimension of Bucket : Depth of the bucket 0.8 d to. d Radial height d to 3d Axial width 3d to 5d 64. Ans : (c) Ratio of width of bucket to jet diameter is 3 to Ans : (b) ead available 37.5 m Q Discharge of water m 3 /sec ower (in watt) gq Watt kw [ kw] Ans : (c) ower obtained from the turbine shaft Frictional losses (or) Mechanical loss ydraulic loss in runner ower supplied by water at entry of turbine i.e. shaft water ydraulic losses in runner + mechanical losses 69. Ans : (a) hyd 7. Ans : (a) m 73. Ans : (a) ower from runner of turbine ydraulic power at entry of runner wheel Shaft power ower produced by turbine h ydraulic efficiency ower developed by the runner ower supplied by the water at entrance of wheel m vol ower of the runner shaft ower supplied by the water to runner Similarly other efficiencies in case of pelton wheel are volume of water actually strike the runner volume of water supplied to the runner o h m 75. Ans : (c) Shaft power Water power Overall efficiency of a pelton wheel varies from 85% to 90% 77. Ans : (b) Transmission 78. Ans : (a) ower available at the end of penstock ower supplied at entry of penstock Maximum hydraulic efficiency of a pelton wheel 4

5 W.D/sec F U h K.E of Jet/sec m w w m U m U w m m U w w From velocity diagrams of a pelton wheel bucket. Where, r w cos U w r U h U cos U U U cos U Differentiate with respect to U for maximum efficiency d h d U cos i.e. U & 0 hydmax hydmax 79. Ans : (b) 0 cos cos Condition for maximum efficiency of a pelton wheel is Where, U U Tangential velocity of wheel elocity of water jet at inlet of turbine O/ W.D/sec F U I/ K.E/sec mv m. r U r.u m U U Differentiate with respect to U for maximum hydraulic efficiency U 0 U U 0 d(u) d ote : For maximum ydraulic efficiency, wheel velocity should be half of the jet velocity. 85. Ans : (a) Francis water turbine is classified as medium head, radial inward flow, medium specific speed, medium discharge and reaction type turbine. ote : Kaplan & ropeller turbines are classified as low head, axial flow, high specific speed, high discharge and reaction type turbines.. Modern Francis turbine is mixed flow turbine i.e radial inward and axial out flow turbine.. In inward flow reaction turbine water enters at outer periphery of runner and flows out from the centre of the runner. 3. In reaction turbine (Francis turbine) part of head is converted into velocity before enters the runner 5

6 94. Ans : (d) Water enters the turbine at high pressure and low velocity is a type of reaction turbine [Ex: Francis & Kaplan, propeller type] ote : Water enters at atmosphere and high velocity is a type of impulse turbine (Ex : elton wheel). Francis turbine is radial flow type turbine. Kaplan & ropeller turbine areaxial flow type turbines. 05. Ans : (d) Euler's equation of energy transfer in hydraulic turbines gives theoretical power developed by it. ower developed by turbine F U Tangential force Tangential velocity of runner ma U m () whirl U w w m U mw U w U 06. Ans : (c) ower developed by a reaction turbine o g.q. (Watt) Watt 943 kw [ kw] Ans : (c) 4000 T kw 55 kw 08. Ans : (d) m Q 0 m 3 /s 0 k/m 3 Shaft power,? Q MW 09. Ans : (b) Reaction turbines (Francis, Kaplan, & ropeller type) are mounted vertically and coupled with electric generator in order to take advantage of head available maximum. Bottom most portion is turbine and above it is generator and both are coupled in vertical position. Impulse turbine shaft is generally horizontal arranged since flow of jet is tangential. 0. Ans : (b) Speed ratio of a Francis turbine range is 0.6 to 0.9 S.o. Speed ratio of pelton wheel range is Type of Turbine. elton wheel Francis turbine Kaplan & ropeller.8.5. Ans : (a) Given data : Flow ratio () 0.4 alue of g 00 m/s Area of flow (A f ) 6m Speed of ratio( ) U gh Discharge (Q) through turbine?(m /sec) Flow Ratio, f g 6

7 3. Ans : (b) 0.4 f 00 f 40 m/sec Q A f f m 3 /sec umber of blades on runner of a kaplan turbine 3 to 6 ote: Francis turbine runner has 6 to 4 blades 4. Ans : (b) Theoretical discharge through Francis turbine (Q) A f. f A f. f Actual discharge K.W K.A.v K.A.v f f f f Where, kdbv f K vane factor 5. Ans : (d) Discharge through Kaplan turbine is given by Q A D D 4 Where, 6. Ans : (a) f f o b f D o Outer diameter of the runner D f Diameter of hub portion of runner Low head & Low power turbine is a Kaplan turbine. 7. Ans : (c) ower generated o Q 9. Ans : (a) kw Draft tube : It is a vertical tube which connects outlet of reaction turbines (Francis, Kaplan & propeller) with the tail race crosssectional area gradually increases towards the tail race i.e. outlet of it. (maximum divergent cone angle of tube is 8 ) It is required to perform the following : (i) It allows to install the reaction turbines above the tail race without loss of head. This makes the inspection and maintenance of turbine easy (safety aspects also) (ii) Outlet of reaction K.E is converted to pressure head, there by head on turbine increases. Efficiency of draft tube : Draft tube Actual regain of pressure head elocity head at entrance h g g If h f is neglected Draft tube f ote : Draft tube is not required for an Impulse turbine (elton wheel) as this turbine works in open atmosphere. 3. Ans : (d) Draft is used for reaction turbine i.e. Francis & Kaplan turbines. 35. Ans : (d) Degree of Reaction (D.O.R) of a turbine is defined as the ratio of pressure energy change to total energy change inside the turbine runner. D.O.R r.e change inside runner T.E change inside runner For elton wheel : (U U ) D.O.R 0 0 7

8 36. Ans : (d) Governing of a turbine : The governor varies the water flow through the water turbine to control is speed according to load of electrical generator. 37. Ans : (c) Functions of governor : It can automatically adjust the rotating speed of hydroelectric generator, keeping them running with in the allowable deviation rated speed, so as to meet the requirements of power grid frequency quality. It quickly makes hydroelectric generating set automatically or manually starting to adapt to the power grid load's increase and decrease, and the needs of the normal downtime or emergency stop. When it runs in parallel with hydroelectric generating set in the power system, the governor can be automatically scheduled for the load distribution, and make each unit to achieve economic operation. 38. Ans : (d) Types of Governors : Governors are classified into : Impact governor, monotone, dual regulating. The impact governor applies to the impulse turbine (elton wheel) unit; the drab applies to the mixed-flow turbines or axial flow turbine (Reaction type); the dual governor applies to the movable propeller turbine and bulb tubular turbine with the adjustment of wheel blade. All types of water turbines use "oil pressure governor" 39. Ans : (c) The runaway sped of a water turbine is its speed at full flow, and no shaft load (Electric generator not coupled). The turbine is to be designed to survive the high mechanical forces of this speed. The manufacturer will supply the runway speed rating. 46. Ans : (a) 60f synchronous 300 p Ans : (c) Specific speed ( s ) of a turbine : It is defined as the rotational speed at which a water turbine would operate at best efficiency under unit head ( m) and which is sized to produce unit power (k W). s is given by 5/4 Where turbine runner wheel (rpm) shaft power (kw) ead on turbine (m) Classification of water turbines based on : Specific Speed range : Specific S.o. Turbine type ead (m) Speed Turgo 0 80 Cross flow 0 70 (Bank) 3 elton Wheel Francis mto 300 m 5 mto 00m 300 mto 000m 30 mto 300 m 4mto 5 Kaplan m 8

9 57. Ans : (c) 0 m (low head turbine) i.e. Kaplan turbine 64. Ans : (b) Impulse type 0 00 Reaction type Axial type 75. Ans : (a) Given data : 600 kw 360 rpm 8 m s The range is valid for "Kaplan turbine" 76. Ans : (a) kw 7463 kw 4.7 m 80 rpm s The range is valid for "Francis turbine". 77. Ans : (b) kw kw 6 m 00 rpm s The range is valid for "Francis turbine". 78. Ans : (d) 7360 kw 8 m 500 rpm s The range is valid for "Francis turbine". 79. Ans : (a) 500 kw 300 rpm 50 m s s < 30, ence elton wheel with one nozzle used. 80. Ans : (b) s The range is valid for "Kaplan turbine" 8. Ans : (b) 0 m 375 rpm 400 kw s The range is valid for "Francis turbine". 8. Ans : (d) kw 8 m 500 rpm s 56 T The range is valid for "Francis turbine". 9

10 83. Ans : (b) s 500 T 5/ Ans : (c) omologous and similar geometrical turbines should have same Specific speed. SModel m 87. Ans : (b) Srototype m p p 5/4 5/4 m p 8. s 5/ /4 s 8. 6 s Ans : (a) 9.3 s 5/ /4 5/4 8. 5/ Ans : (b) More efficiency under part load operation is observed in case of Kaplan turbine only. 9. Ans : (a) Kaplan turbine igh part load efficiency elton wheel Works in open atmosphere Axial flow machine igh Sp. Speeds Draft tube ressure head recovery 93. Ans : (b) Unit speed ( U ) : It is defined as the speed of a water turbine working under a unit head u 94. Ans : (b) Unit Discharge (Q) : It is defined as the discharge passing through a turbine, which is working under a unit head. Q Q U 96. Ans : (c) Q Q Unit ower ( u ) : It is defined as the power developed by a turbine, working under a unit head. s s Ans : (d) Kaplan turbine is to be superior to other turbines from consideration of high power generation on account of better overall efficiency. u 3 3/ 3/ 0

11 99. Ans : (c) Ans : (c) 750 kw 00 m Unit power, kw 00 u Ans : (c) 0 u 3/ 5 0. Ans : (d) 0.08 kw kw 36 u 3/ 3/ 03. Ans : (a) Q 400 m 3 /sec 0 m Q 400 Qu 36.5 m 3 /sec Ans : (a).d 3 A D D Q 05. Ans : (b) u 06. Ans : (a) u 07. Ans : (b) 600 kw, 30 m, 450 rpm u rpm u 3/ 3/ 600 3/ 3/ kw 08. Ans : (b) u n Where, 09. Ans : (d) 3 n.5 Turbine constants like u, Q u and u are used to plot performance curves. 0. Ans : (a) Curved vanes are preferred over flat vanes in hydraulic machines due to advantage of more energy transfer possible between working fluid and contact surface.. Ans : (a) Operating characteristic curves of a turbine are plotted when the speed on the turbine is constant; and are constant and variation of power () and efficiency () with respect to discharge (Q) are plotted. 3. Ans : (b) Characteristic curves of a turbine means main characteristic curves only. These curves are plotted by maintaining a constant head. Speed of the turbine varies by changing load on the turbine.

12 4. Ans : (c) In impulse turbine, water impinges on the bucket with K.E. ressure of flowing fluid remains unchanged (i.e. in open atmosphere). In reaction turbine, water glids over the moving vanes with.e. ressure of flowing fluid decreases after gliding over the vanes. 6. Ans : (a) Cavitation in a hydraulic machine like water turbine causes erosion on the surface of runner, high frequency waves produces noise & vibrations. 0. Ans : (c) Forebay tank (or) reservoir forms the connection between the power channel and the penstock. It also serve as a reservoir to store water. When hydel plant is located at base of the dam, no forebay is required because reservoir acts as forebay. Ex : agarjuna sagar project does not have fore bay. When plants are located away form the storage reservoir forebay is needed. Forebay provides steady and continuous water flow into the penstock/ turbine Fore bay ower Channel U/S River D/S enstock To River Dam ydraulic ower ouse Tail race. Ans : (a) Trash rack : Is a metal frame provide in front portion of sluice gate of penstock to keep out debris and not to allow floating and suspended materials into penstock.. Ans : (b) ondage : Small water storage behind weir of run-of-river hydel plants. It is less storage than reservoir less dams. Weir : Weir is necessary for surplus water to pass over it. Dam : Dam is necessary for build the head of water. 3. Ans : (a) umbp storage plant turbine is used during peak terms of electrical power demand and later same turbine is used as pump to lift water from tail race to reservoir with help of power from other source i.e. thermal energy generated electrical power. 4. Ans : (b & c) Base power : It is power consistently generate the electric power needed to satisfy minimum demand. This is the minimum level of demand on an electrical grid over 4 hours. For India, base power is thermal power.

13 Firm ower (or) rimary power : This power is always available and corresponds tot he minimum water stream flow and adverse hydrologic conditions in a river. Firm power can be defined as the minimum power which can be generated throughout the year. By providing storage of water the firm power can be increased considerably. Installed capacity : It is the maximum power generation can produce under available specific conditions at site. Installed capacity is the amount of electric energy that a hydel power station is able to produce under specific conditions. 5. Ans : (a) A common fault that arises in a hydraulic system is air lock. 9. Ans : (a) Load factor is the ratio of average load on the hydal plant during the period considered. 3. Ans : (b) t a 4.5 sec v 500 m/s l 3000 m t c L sec C 500 t a >t c Slow closure 33. Ans : (o answer) 0 gq kw 34. Ans : (a) d 5 m/sec a S hf g g g m 35. Ans : (a) In a pelton wheel, The component of absolute velocities, w C gh v C v 0.98 h 30 m m/s 378 cm/s 3