Hydraulic Turbines

Lecture slides by

Sachin Kansal

NATIONAL INSTITUTE OF TECHNOLOGY

KURUKSHETRA

2

Objectives

• To have an understanding of working of Hydro-Power

Plant and Hydraulic Turbines

• To have an understanding of classification of various

types of turbines

• To know about the various types of heads associated

with a hydro-power plant

• To understand the different types of efficiencies arising

due to losses at various instances

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Sardar Sarovar Dam

(Narmada River , Gujarat)

1450 MW

Nathpa Jhakri Hydroelectric power

project (Satluj, Himachal Pradesh)

1530 MW

Koyna Dam

(Koyna River,Maharashtra)

1960 MW

Giant Hydro Power Plants of India

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Introduction

Hydraulic Turbines are defined as the hydraulic machines

which convert hydraulic energy into mechanical energy

This mechanical energy is used in running an electric

generator which is directly coupled to the shaft of the

turbine.

Thus the mechanical energy is converted into electric

energy.

The electric power, which is obtained from the hydraulic

energy is known as Hydro-electric power.

At present, the generation of hydro-electric power is the

cheapest as compared to the power generation by other

sources such as oil, coal, etc.

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6

Components of Hydropower Plant

Reservoier• Natural (Lakes on Mountains) or Artificial (Dams)

Head Works

• Equipment used to control water into waterways

• e.g. Gates, Valves, Fish-traps etc.

Water Ways

• Passage to take water from reservoir to power house

• e.g. Penstock, Tunnels, Channels etc.

Forbays or Surge Tank

• To meet the load fluctuations for small period as for a day

• Situated at the end of a tunnel or open channel

Powerhouse and Tail Race

• Consist of turbine, generator etc.

• Tailrace is waterways takes the water from the turbine outlet into channel or river.

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Fig. – Layout of Hydroelectric Power Plant using an Impulse Turbine

Turbines

(a) According to the type of

energy at the inlet

(i)

Imp

uls

e T

urb

ine

(ii) R

ea

ctio

n T

urb

ine

(b) According to the direction of

flow through runner

(i)

Ta

ng

en

tia

l F

low

Tu

rbin

e

(ii) R

ad

ial F

low

Tu

rbin

e

(iii)

Axia

l F

low

Turb

ine

(iv)

Mix

ed

Flo

w T

urb

ine

(c) According to the head at the

inlet of the turbine

(i)

Hig

h H

ea

d T

urb

ine

(ii) M

ed

ium

He

ad

Tu

rbin

e

(iii)

Lo

w H

ea

d T

urb

ine

(d) According to the specific speed of the

turbine

(i)

Lo

w S

pe

cific

Sp

ee

d

Tu

rbin

e

(ii) M

ed

ium

Sp

ecific

S

pe

ed

T

urb

ine

(iii)

Hig

h S

pe

cific

Sp

ee

d

Tu

rbin

e

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Classification of Hydraulic Turbines

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(a) According to the type of energy at

the inlet (i) Impulse Turbine

All the available energy of the water is converted into

kinetic energy or velocity head by passing it through a

convergent nozzle provided at the end of the penstock.

So, at the inlet of the turbine, only kinetic energy is

available

Pressure of water flowing over the turbine blades

remains constant (i.e. atmospheric pressure)

Examples: Pelton wheel, Turgo-impulse turbine, Girard

turbine, Banki turbine, Jonval turbine, etc

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(ii) Reaction Turbine

At the entrance to the runner, only a part of the available

energy of water is converted into kinetic energy and a part

remains in the form of pressure energy.

So at the inlet of the turbine, water possesses kinetic

energy as well as pressure energy.

As the water flows through the turbine blades, the change

from pressure energy to kinetic energy takes place

gradually.

For this gradual change of pressure, the runner must be

completely enclosed in an air-tight casing and the passage

should be full of water.

The difference of pressure between the inlet and outlet of

the runner is called reaction pressure ,and hence these

turbines are known as reaction turbines.

Examples: Francis turbine, Kaplan turbine, Propeller

turbine, Thomson turbine, Fourneyron turbine etc

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Aspect Impulse Reaction

Fluid energy conversion K.E. in the nozzle K.E. in the fixed blade

Flow path Nozzle-runner Fixed blade – runner

Energy inlet to moving

blades

Only K.E. K.E. + P.E.

Changes in pressure &

velocity

Pressure =Constant P & V both changes

Entering of water Water may be admitted

over apart or whole

circumference of runner

wheel

Must admitted over whole

circumference of runner

wheel

Water fills the turbine Not required wheel run full Run full and kept full of

water

Flow regulation Possible Not

Casing Prevent splashing & guide

water to tail race

Water tight casing is

required & has to sealed

from atm.

Governing Needle valve Guide blade

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(b) According to the direction of flow

through runner(i) Tangential flow turbine

In tangential flow, the water strikes the runner in the direction

of the tangent to the path of rotation of the runner. OR

The water strikes the vane/bucket along the tangent of the

runner.

Example: Pelton wheel

(ii) Radial flow turbine

In radial flow, water flows through the turbine along the

direction normal to the axis of rotation (i.e. radial direction).

A radial flow turbine is further classified as inward or outward

flow depending upon whether the flow is inward from the

periphery to the center or outward from the center to

periphery.

Example: Old Francis turbine

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(iii) Axial flow turbine

In an axial flow turbine, water flows along the direction

parallel to the axis of rotation of the runner.

Here the water flows parallel to the turbine shaft.

Examples: Kaplan turbine, Propeller turbine

(iv) Mixed flow turbine

In mixed flow, water enters the runner in the radial direction

and leaves in the direction parallel to the axis of rotation

(i.e. axial direction)

Example: Modern Francis turbine

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(c) According to the head at the inlet of

the turbine(i) High head turbine

High head turbines which operate under high head (above

250m) and require relatively less quantity of water

Example: Pelton wheel turbine

(ii) Medium head turbine

Medium head turbines which operate under medium head

(60m to 250m) and require medium flow rate.

Example: Modern Francis turbine

(iii) Low head turbine

Low head turbines that operate under head up to 30m and

require a very large quantity of water.

Example: Kaplan and Propeller turbine

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(d) According to the specific speed of

the turbine(i) Low specific speed turbine

For Pelton wheel turbine with a single jet,

𝑁𝑠 = 8.5 𝑡𝑜 30

For Pelton wheel turbine with the double jet,

𝑁𝑠 = 40

Medium specific speed turbine

For Francis turbine,

𝑁𝑠 = 50 𝑡𝑜 340

High specific speed turbine

Kaplan and other Propeller turbines,

𝑁𝑠 = 255 𝑡𝑜 860

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Efficiencies & Head of Hydraulic

TurbinesGross Head (𝑯𝒈)

It is the difference between the headrace level and tail race

level when no water is flowing

It is also known as the total head of the

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Effective Head or Net Head (H)

A net head or effective head is the actual head available at

the inlet of the turbine

When water is flowing from the headrace to the turbine, a

loss of head due to friction between water and penstock

occurs.

Though there are other losses also such as loss due to

bend, pipe fittings, loss at the entrance of the penstock, etc.

These all having small magnitude as compared to head

loss due to friction.

So,𝐻 = 𝐻𝑔 − ℎ𝑓, where 𝐻 = Net head or Effective head

𝐻𝑔 = Gross head

ℎ𝑓 = Head loss due to friction between penstock and water = 4𝑓𝐿𝑉2 / 2𝑔𝐷

𝑓 = Coefficient of friction of depending on the type of material of penstock

𝐿 = Total length of penstock

𝑉 = Mean velocity of water through the penstock

𝐷 = Diameter of penstock and

𝑔 = Acceleration due to gravity

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Hydraulic Efficiency (𝜼𝒉 )

It is the ratio of the power developed by the runner of a

turbine to the power supplied by the water at the inlet of a

turbine.

Since the power supplied is hydraulic, and the probable

loss is between the striking jet and vane it is rightly called

hydraulic efficiency

Mechanical Efficiency (𝜼𝒎 )

The power delivered by water to the runner of a turbine

is transmitted to the shaft of the turbine.

It is the ratio of the power available at the shaft of the

turbine to the power developed by the runner of a turbine

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This depends on the slips and other mechanical problems

that will create a loss of energy i.e. friction

Overall Efficiency (𝜼O)

It is the ratio of the power available at the shaft to the

power supplied by the water at the inlet of a turbine

Euler’s Equation and Degree of

ReactionWork done or energy transfer in case of radial curved

vanes = E/unit mass-sec= 𝑉𝑤1 𝑢1 ± 𝑉𝑤2 𝑢2

This fundamental equation of hydraulic machines are

known as Euler’s Equation, applicable to both turbines and

pump

If E= +ve, then Energy is transferred from the water to

wheel , which gives motion to that and is principle of motion

of turbines

If E= -ve, then Energy is transferred from wheel to water ,

which can raise its velocity or pressure, which is principle of

motion of centrifugal pump

Transformation of equation in another form

21

2

2

2)(

2

)(

TriangleVelocity Inlet From

21

21

2

11

21

21

211

112

12

12

122

1

112

12

12

12

1

112

1

1

1

1

2

rw

rw

wwwr

wwfr

wrw

VuVuV

VuVuV

uVuVVVV

uVuVVV

uVV

2

2

2)(

2

)(

TriangleVelocity Outlet fromSimilarly

22

222

22

22

22222

222

22

22

222

2

222

22

22

22

2

222

2

2

2

2

2

uVVuV

uVVuV

uVuVVVV

uVuVVV

uVV

rw

rw

wwwr

wwfr

wrw

22

222

22

,

21

22

22

21

22

22

222

21

21

2

21

21

21

21

rr

rr

ww

VVuuVVE

uVVVuVE

uVuVENow

Dynamic

Energy

Change:Difference in

square of

absolute

velocities or

change in K.E

of the liquid

Centrifugal

Energy

Change::Difference in

square of

tangential

velocities or

change in

centrifugal

head and

pressure

change due to

that

Pressure

Energy

Change::Difference in

square of

liquid velocity

or pressure

change due to

change in

relative

velocity

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∴

Degree of Reaction : Ratio of Energy conversion inside therunner to the total energy conversion

ChangeEnergy Total

ChangeEnergy Pressure ChangeEnergy lCentrifugaReaction of Degree

For Impulse Turbine, flow is tangential (u1=u2), pressure is atmospheric and

vane is smooth (Vr1=Vr2)

Energy Change is only due to change in K.E. of the liquid

In reaction turbine, if flow is axial then u1=u2

Energy change is due to change in K.E and Pressure Energy

In reaction turbine, if flow is radial or mixed, all the three terms are effective

2

2221 VV

E

22

21

22

2221 rr VVVV

E

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Reference Links

• Types of Fluid Machines: https://youtu.be/TiJZp-KB6h8

https://youtu.be/Lu4oKZXSAyQ

• Euler’s Equation https://youtu.be/6Opq1_RfsOo

https://youtu.be/pzKWoMPh4Xg