basic mechanical engineering- hydraulic turbines

HYDRAULIC TURBINES

Prepared by,

M.S.Steve,Assistant Professor,Amal Jyothi College of EngineeringEmail: [email protected]

DEFINITION

• Hydraulic turbine – A rotary engine that converts hydraulic energy into mechanical energy.

• Mechanical energy is used in running an electric generator which is coupled to turbine shaft.

M.S.Steve/ 9745917858/[email protected]

CLASSIFICATION OF TURBINES …(1)

• According to the type of energy at inletImpulse turbineReaction turbine


IMPULSE TURBINE

• Energy available at the inlet of the turbine is only kinetic energy.

• Pressure is atmospheric from inlet to outlet.• Works on the basis of impulse momentum

principle• Eg: Pelton Wheel


PELTON WHEEL OR PELTON TURBINE ..(1)

• Named after American Engineer L.A.Pelton• Energy available at inlet is only kinetic energy.• Used for high heads.


PELTON WHEEL ..(2)

PELTON WHEEL ..(3)

• Water from reservoir flows through penstocks.• At the outlet of penstock nozzle is fitted.• Nozzle converts hydraulic energy of water into kinetic

energy.• Water striking the nozzle is controlled using a spear.• Water comes out as a jet from nozzle and strikes the

buckets (vanes) which are fixed on the periphery of a wheel.

• Casing is used to prevent splashing of water.


PELTON WHEEL ..(4)

Double cup shaped Runner buckets-Cast steel or Bronze

PELTON WHEEL ..(5)

REACTION TURBINE

• Energy of fluid partly transferred into kinetic energy before it enters the runner

• It enters the runner with excess pressure.• Pressure energy is converted into kinetic energy as

water passes through runner.• The difference in pressure between inlet and outlet

of runner (reaction pressure) is responsible for motion of runner.

• Eg: Francis turbine, Kaplan Turbine


FRANCIS TURBINE … 1

• Named after American Engineer J.B.Francis

• It is a mixed flow reaction turbine with medium head and medium specific speed

FRANCIS TURBINE COMPONENTS

• Penstock• Scroll/Spiral casing• Speed ring/Stay ring• Stay vanes• Guide vanes/Wicket vanes• Runner blades• Draft tube

FRANCIS TURBINE-WORKING

• Water from the penstock enters the scroll casing which

completely surrounds the runner.

• Involute casing provides an even distribution of

water(constant velocity) around the circumference of

the runner.

• Stay rings directs water from scroll casing to guide

vanes.M.S.Steve/ 9745917858/[email protected]


• The guide vanes -regulate the quantity of water supplied to the runner(to take care of the load variations) -direct water to the runner at an appropriate angle.

• The runner consists of a series of curved vanes evenly arranged around the circumference.

• At the entrance to the runner only a part of energy of water is converted into kinetic energy and substantial part remains in the form of pressure energy.

• As water flows through the runner the change from pressure to kinetic energy takes place gradually.



• The difference in pressure between the inlet and

outlet of the runner is called reaction pressure.

• Water enters the runner from the guide vanes

towards the centre radially and discharges out

axially- Mixed flow turbine.

• After doing work water is discharged to the tail

race through a closed tube of gradually enlarging

section called draft tube.M.S.Steve/ 9745917858/[email protected]

FRANCIS TURBINE …1

KAPLAN TURBINE …1

• Developed by Austrian Engineer V. Kaplan.• Suitable for relatively low heads and requires

large volume of water to develop large power.• Kaplan turbine is a reaction turbine in which

water enters and leaves the runner blades axially-Axial flow turbine


KAPLAN TURBINE- COMPONENTS

Scroll casingGuide VanesRunner VanesDraft tube

KAPLAN TURBINE- COMPONENTS ...2

• The shaft of an axial flow reaction turbine is vertical.

• The lower end of the shaft is made bigger and is known as hub or boss.

• The runner vanes are fixed on the hub or boss.


KAPLAN TURBINE- WORKING

• Kaplan turbine works on the reaction principle as Francis turbine.

• Only difference is that water enters and leaves the turbine axially – Axial flow turbine.

• Both the guide vane(wicket gate) angle and runner vane angle can be adjusted which gives rise to high efficiency.

KAPLAN TURBINE …1

KAPLAN TURBINE …2

Classification of Hydraulic Turbines.

• Based on action of water

• Based on the main direction of flow

• Based on the head and quantity of water

required.

• Based on the specific Speed


Classification based on direction of Flow

• Tangential flow: Pelton Turbine

• Axial Flow Turbine: Kaplan Turbine

• Radial Flow Turbine:Inward: Thomson Turbine

• Mixed Flow Turbine : Modern Francis Turbine


Classification Based on Head Available

High Head Turbine(High head & low discharge)Head ranges from several hundred to thousand meterse.g. Pelton Turbine(250 to 2000m)

Medium head Turbine(Medium head and medium discharge)Head ranging from 50m to 250me.g. Modern Francis Turbine

Low Head Turbine(low head high discharge)Head less than 50me.g. Kaplan Turbine , propeller turbine

Specific speed of Turbine

• It provides the means of comparing the speed of all type if turbine on the same basis of head and power.

• Specific speed of a turbine is defined as the speed at which turbine run developing unit power under unit head .


SPECIFIC SPEED …1

• Speed of a geometrically similar turbine that would develop 1 kW power when working under a head of 1 m. (in SI system)

• All geometrically similar turbines will have the same specific speed when operating under the same head, irrespective of its size.

• Specific speed of a turbine is obtained using

4/5HPNNS

Where Ns=Specific speed ,N = speed in rpm H=effective head in m ,P= Power output in kW

CLASSIFICATION OF TURBINE BASED ON SPECIFIC SPEED

• According to the specific speed of the turbineHigh specific speed turbineMedium specific speed turbineLow specific speed turbine

HIGH SPECIFIC SPEED TURBINE

• A turbine of higher specific speed will have a higher speed of rotation of the turbine runner

• So a small diameter runner can develop high peripheral velocity

• It allows reduction in runner diameter as well as the overall size of the runner for a given head and power output.

• It will further reduce the weight and cost of the runner.

• Hence high specific speed turbines are used for low head applications like Kaplan turbine.(255-860)

MEDIUM SPECIFIC SPEED TURBINES

• Francis turbine has medium range of specific speed

• Its value ranges from 50 to 340 in SI units for a Francis turbine


LOW SPECIFIC SPEED TURBINES

• Low specific speed turbines are used for high head turbines

• A runner of too high specific speed with high available head will increase the cost of the turbine on account of the high mechanical strength required

• Eg: Pelton turbine(8.5 to 30)


Selection of turbines

Type of turbine Range of head Specific speed in metric units

Pelton 200-2000 10-15

Francis 15-300 80-420

Propeller 5-30 310-1000

Thank You

@msstevesimon

2m.s.steve

basic mechanical engineering- hydraulic turbines

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