featuring about water turbine

1. FLUID MACHINES
Chapter 3: Water Turbine
Presented by
Keshav Kumar Acharya
Teaching Assistant
TU, IOE
Purwanchal Campus

2. Specific energy
The specific energy of a hydro power plant is the
quantity of potential and kinetic energy which 1
kilogram of the water delivers when passing
through the plant from an upper to a lower
reservoir.
The expression of the specific energy is Nm/kg or J/kg
and is designated as m2/s2.

3. Gross Head
Hgr
Reference line
zres
ztw
twresgr zzH 

4. Gross Specific Hydraulic Energy
In a hydro power plant, the difference between the
level of the upper reservoir zres and the level of the
tail water ztw is defined as the gross head:
Hgr = zres - ztw [m]
The corresponding gross specific hydraulic energy:
][ kgJHgE grgr 

5. Gross Power
grgrgr HgQEQP  
Where:
Pgr is the gross power of the plant [W]
 is the density of the water [kg/m3]
Q is the discharge [m3/s]

6. Definition of heads
• Gross head (Hg):
– the difference between the head race level and tail
race level when no water is flowing
• Net head:
– also called effective head
– the head at the inlet of the turbine
• When water is flowing from head race to the turbine, a
loss of head due to friction between the water and
penstocks occurs as a major losses
fgn hHH 

7. Classification of the turbines
Hydraulic turbines are classified based upon:
• Energy available at the inlet of the runner:
e.g. impulse and reaction turbine
• Direction of the flow through the runner:
e.g. tangential flow, radial flow, axial flow & mixed flow
• Head at inlet of turbine:
e.g. High head, medium head and low head
• According to specific speed:
e.g. low sp. speed, medium sp. speed & high sp. speed
• According to speed number:
e.g. low speed no., medium speed no. & high speed no.

8. Impulse turbines
(Partial turbines)
The hydraulic energy is completely converted to
kinetic energy before transformation in the runner
212121 ; wwandvvpp  (neglecting losses in buckets)

9. Impulse turbines
(Partial turbines)
Turgo Pelton

10. Reaction turbines
(Full turbines)
In the reaction turbines two effects cause the energy
transfer from the flow to mechanical energy on the turbine
shaft.
Firstly it follows from a drop in pressure from inlet to outlet
of the runner. This is denoted the reaction part of the
energy conversion.
Secondly changes in the directions of the velocity vectors
of the flow through the canals between the runner blades
transfer impulse forces. This is denoted the impulse part of
the energy conversion.
212121 ; wwandvvpp 

11. Reaction turbines
(Full turbines)
Francis Kaplan Bulb

12. Impulse versus Reaction turbines
Aspects Impulse turbines Reaction turbines
Conversion
of fluid
energy
The available fluid energy is
converted in to K.E. by a
nozzle
Only a portion of the fluid energy is
transformed into K.E. energy before
the fluid enter the turbine runner
Change in
pressure &
velocity
The pressure remains
same (atm.) throughout the
action of water on the
runner
After entering the runner with an
excess pr., water undergoes changes
both in velocity and pr. while passing
through the runner
Admittance
of water over
the wheel
Water may be allowed to
enter a part or whole of the
wheel circumference
Water is admitted over the
circumference of the wheel
Role of
casing
No hydraulic function to
perform; it only serves to
prevent splashing and to
guide the water to the tail
race
Pr. at inlet to the turbine is much
higher than the pr. at outlet; unit has to
be sealed from atmospheric conditions
and therefore , casing is absolutely
essential

13. Impulse vs. Reaction turbines
contd..
Aspects Impulse turbines Reaction turbines
Relative velocity
of water
Either remaining constant or
reduces slightly due to
friction
Due to continuous drop in pr.
during flow through the blade, the
relative velocity increase
Installation of unit Always installed above the
tail race. No draft tube is
used
Units may be installed above or
bellow the tail race and use of
draft tube is made
Flow regulation By means of needle valve
fitted into the nozzle
By means of guide vane
assembly
Action on blades Blades are only in action
when they are in front of the
nozzle
Blades are in action all the time
Extent to which
the water fills the
turbine
Turbine does not run full
and air has a free access to
the buckets
Water completely fills all the
passages throughout the
operation of the turbine

14. Unit and Specific Quantities
• Rate of flow, speed, power, etc. of hydraulic machines are all
functions of working head
• To facilitate correlation, comparison and use of experimental
data, these quantities are usually reduced to a unit heads
• Each is expressed as a function of head and its value
corresponding to a unit value of head is determined
• These reduced quantities are known as Unit Quantities
• Eg: unit flow, unit speed, unit force, unit power, unit torque,
etc.
• Two similar turbines having different data can be compared by
reducing data of both turbines under unit head

15. Unit and Specific Quantities
• A Specific Quantity is obtained by reducing any quantity to a
value corresponding to unit head and some unit size
• The later dimension being inlet diameter of runner in case of
reaction turbines and jet diameter in case of Pelton turbines
• Specific flow is the rate of flow corresponding to unit head and
unit diameter
• Specific power is the power corresponding to a unit head and
unit diameter
• But Specific Speed of a turbine is defined as the speed of a
geometrically similar turbine working under a unit head and
developing unit power
• Specific speed is the modern basis of scientific classification
of turbines and pumps

16. Specific speed
4
5
H
pN
Ns


Specific speed is the speed of geometrically similar turbine (i.e., a turbine
of identical in shape, dimensions, blade angles and gate opening etc.)
with the actual turbine but such a size that would develop unit power
when working under a unit head.
Specific speed provides a basis on which different types of turbines can be
compared irrespective of their sizes, which is proportional to the speed of
rotation and inversely proportional to the head.
This mean that:
High speed Propeller type turbines (Kaplan turbine) are expected to have
high specific speeds than relatively low machine (Pelton turbines) and
the high head machines (Pelton) would have low value of specific
speed than the Francis and Kaplan units which operate under medium and
low head
Where,
N = rpm, p = kW and H = m

17. Classification of the turbines based
upon specific speed
S.N. Type of turbine Head H (m) Specific speed
(Ns)
1 Pelton with 1 jet Up to 2000 12 to 30
2 Pelton with 2 jets Up to 1500 17 to 50
3 Pelton with 4 jets Up to 500 24 to 70
4 High head Francis Up to 300 80 to 150
5 Medium head Francis 50 to 150 150 to 250
6 Low head Francis 30 to 60 250 to 400
7 Propeller and Kaplan 4 to 60 300 to 1000
8 Bulb or tubular turbines 3 to 10 1000 to 1200

18. Speed number
Q***

Geometric similar, but different sized turbines have the
same speed number
D
Hg 

2
*


Hg
Q
Q


2
*
Where,

19. Classification of turbines based
upon speed number
* < 0.22 0.2 < * < 1.25 * > 1.0
1.0 < * < 1.25 Francis/ Kaplan ???

20. Specific speed that is used to
classify turbines

21. Selection of hydraulic turbines
• Specific speed
• Rotational speed
• Efficiency
• Part load operation
• Overall cost
• Cavitation
• Disposition of shaft
• Number of units
• Head
• Sediment erosion

22. Problems
• Find the speed number & specific speed of a turbine
installed at a site, which develops 12,940 kW under a
head of 510 m when running at 300 rpm. Specify the
type of the turbine employed. Does this valid from both
approach?
• The turbine installed at one particular power house
develops 2.54 MW under a head of 29.9 m. Find the
specific speed of this turbine if it runs at 166.7 rpm.
Knowing the specific speed, what type of runner would
you select for such a turbine?
• An impulse turbine develops 1.865 MW under a head
70 m. What could be the maximum and minimum
speeds of the turbine with a single nozzle? What
speed would be the best for coupling to an alternator ?
How high a speed could a reaction turbine give?