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1. Conduits, Intake, Power house and
Accessories
Lecture 5
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2. Conduits
 a channel for conveying water or other fluid.
 a tube or trough protecting electric wiring.
 A headrace is a channel which leads water to a turbine and a
tailrace conducts water from the wheels.
 The conduit may be open or close.
 Open conduits: canals and flumes
 close conduits: tunnels, pipelines and penstocks
 Canal:- A canal is an open waterway excavated in natural
ground. It has to follow the contour of the ground, with perhaps
a slight gradient corresponding to the head loss.
 The canals are used to convey the water to forebay and these are
may be or open (natural) (or) artificial similar to the natural
water flow rivers. The artificial canals are constructed with use
of concrete lining.
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3. Tunnels
 Tunnels are underground conveyance structures constructed by
special tunneling methods without disturbing the natural surface
of the ground. In many modern high head plants, tunnels form
an important engineering feature.
 In the headrace of water conveyance sytem, tunneling is popular
because of the following reasons:
i) It provides a direct and short route for the water passage thus
resulting in considerable saving in cost
ii) Tunneling work can be started simultaneously at many points
thus leading to quicker completion.
iii)Tunneling work has become easier with development techniques
of drilling and blasting and new mechanical equipment
iv)Development of rock mechanics and experimental stress
analysis has given greater confidence to engineers regarding
stability of tunnels.
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4. Cont’…
 Pipeline. A pipeline is a closed conduit usually supported on or
above the surface of the land. When a pipeline is laid on the
hydraulic gradient, it is called a flow line.
 Tunnels of hydropower projects fall into two categories:.
a) Water carrying tunnels : These include
 Head race tunnels: are tunnels that convey water to the surge
tank. These are pressure tunnels
 Tail race tunnels: could be free flowing or pressure tunnels
depending on the relative position of turbine setting and tail
water level.
 Diversion tunnels: are constructed for the purpose of diverting
the stream flow during construction period. Normally they are
not of high pressure but should have sufficient flood carrying
capacity
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5. Cont’…
b) Service tunnels: These may be:
 Cable tunnels: to carry cables from underground power house
to the switch yard
 Ventilation tunnels: fitted with fans at the open end to supply
fresh air to the underground
 Access or approach tunnels: this is a passage tunnel from
surface to underground power house.
Inlet water ways
 are the passages, through which the water is conveyed to the
turbines from the dam. These may include tunnels, canals, flumes,
forebays and penstocks and also surge anks.
 A forebay is an enlarged passage for drawing the water from
the reservoir or the river and giving it to the pipe lines or canals.
 Tunnels are of two types: pressure type and non-pressure type.
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6. Tail Race or Outlet Water Way
 is a passage for discharging the water leaving the
turbines, into the river and in certain cases, the water
from the tail race can be pumped back into the original
reservoir.
 Spill ways :
 A spill way acts as a safety valve for a dam.
 The capacity of spill way should be such that it
discharges major floods without damage to the dam but
at the same time it keeps the reservoir level below the
predetermined maximum level.
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7. Intake
allows the water to flow into the conduit or penstock
Trash tracks or screens are used to prevent debris passing into
the water passage.
Intake is a structure constructed at the entrance of a power canal
or tunnel or pipe through which the flow is diverted from the
source such as a river or reservoir.
Functions of Intakes
 To control flow of water in to the conveyance system.
 To provide smooth, easy and vortex or turbulence free entry of
water in the conveyance system which is to minimize head loss.
 To prevent entry of coarse river born trash matter such as
boulders, logs, tree branches etc. Provision of trash racks at the
entrance achieve this function.
 To exclude heavy sediment load of the river from interring the
conveyance system. 1/2/2023
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8. Types of Intakes
 Run - of - river intakes
 Canal intakes
 Dam intakes
 Tower intakes
 Shaft intakes
 Intakes of special type
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9. Trash track
They are installed at the intake entrance, upstream of the gate to
prevent trash and debris which might damage the turbines from
entering the water way.
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10. POWER HOUSE
 According to the location, power houses are classified as surface
and/or underground power house.
 The underground power house is built in underground.
 A cavity is excavated inside earth surface where the sound rock
is available to house the power station.
 A surface power house is one which is founded on earth’s
surface and its superstructure rests on the foundation.
 A power house should have a stable structure and its layout
should be such that adequate space is provided around the
equipment (such as turbines, generators, valves, pumps,
governors etc.), so that the dismantling and repairing may be
easily carried out. 1/2/2023
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11. Powerhouse and equipment
A power house, mostly, comprises of the following sub-divisons
or levels
The substructure extends from top of generator to the soil or
rock and houses most of the generating equipment.
Its purpose is to house the passage for the water coming out of
the turbine.
Intermediate structure from the top of the draft tube to top of
generator foundation.
The superstructure lies above the generator level. It houses
mostly the cranes which handle the heavy equipment in the
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12. Substructure
The substructure of a power-house is defined as that part which
extends from the top of the draft tube to the soil or rock. Its
purpose is to house the passage for the water coming out of the
turbine.
In case of reaction turbines, the hydraulic function of the sub-
structure is to provide a diverging passage (known as draft tube)
where the velocity of the exit water is gradually reduced in order
to reduce the loss in pushing out the water.
In case of impulse turbine, such a draft tube is not required and
only an exit gallery would serve the purpose The structural
function of substructure is dual.
The first function is to safely carry the superimposed loads of
machines and other structures over the cavities.
The second function is to act as transition foundation member
which distributes heavy machine loads on the soil such that the
obtainable ground pressures are within safe limits.
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13. Intermediate structure
The intermediate structure of a power house may be defined as
that part of the power house which extends from the top of the
draft tube to top of the generator foundation.
This structure contains two important elements of the power
house, one is the scroll case which feeds water to the turbine.
The generator foundation rests on the scroll-case which is
embedded in the concrete.
The other galleries, adits and chambers also rest on the same
foundation. Scroll or spiral case is a part of the turbine and it
distributes water coming from penstock uniformly and smoothly
through guide vanes to the turbine. The scroll case is required
only in case of reaction turbine.
In case of impulse turbine the place of scroll case is taken by
the manifold supplying water to the jets.
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14. Superstructure
The part of the power house above the generator floor right up
to the roof is known as superstructure.
This part provides walls and roofs to power station and also
provides an overhead travelling crane for handling heavy
machine parts.
Arrangement of reaction and Impulse turbines.
Factors affecting the choice between horizontal and vertical
setting of machines are : relative cost of plant, foundations,
building space and layout of the plant in general.
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15. Cont’…
The pressure type enables the fall to be utilized for power
production and these are usually lined with steel or concrete to
prevent leakages and friction losses.
 The non-pressure type tunnel acts as a channel. The use of the
surge tank is to avoid water hammer in the penstock.
 Water hammer is the sudden rise in pressure in the penstock
due to the shutting off the water to the turbine.
 This sudden rise in pressure is rapidly destroyed by the rise of
the water in the surge tank otherwise it may damage or burst the
penstock.
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16. Cont’…
 Important equipment provided in a power house
 Hydraulic turbines
 Electric generators
 Governors
 Gate valves
 Relief valves
 Water circulating pumps
 Flow measuring equipment
 Air duct
 Switch board equipment and instruments
 Oil circuit breakers
 Reactors
 Low tension and high tension bar
 Storage batteries and Cranes.
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17. Penstock
 It is a closed conduit for supplying water under pressure to a
turbine.
 Tunnels are generally the most costly type of conduit for a given
length but are justified if their use results in considerable saving
in distance.
 Ordinarily tailraces are open channels, tunnels are used for the
discharge from an underground hydro-station.
 Penstocks are used where the slope is too great for a canal,
especially for the final stretch of the diversion system where the
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18. Cont’…
land pitches steeply to the powerhouse.
 Surge tanks or other measures are necessary to prevent
damage in closed conduits due to abnormal pressures.
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19. Cont’…
How to calculate penstock thickness?
The thickness of steel penstock which depends on the water head
hoop/circumferential stress allowed in the material can be
calculated by using the following relation
Where t = Thickness of the penstock,
p = Pressure due to water including water hammer
d = Diameter (internal) of the penstock,
f = Permissible hoop/circumferential stress, and
ή= Joint efficiency.
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20. Cont’…
Number of penstocks to be used:
 To supply water to a number of turbines penstocks
needed may be decided from the following alternatives:
1. To provide one penstock for each turbine separately.
In such a case water is supplied independently to each
turbine from a separate penstock.
2. To use a single penstock for the entire plant. In this
case the penstock should have as many branches as the
number of hydraulic turbines.
3. To provide multiple penstocks but each penstock
should supply water to at least two hydraulic turbines.
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21. Cont’…
 While selecting the number of penstocks to be used for
supplying water to the turbines, the following points are
considered:
(a) Operational safety. As far as possible a single penstock
should not be used for supplying to different turbines for
generating power because any damage to this penstock would
mean shut down of the entire set of turbines.
(b) Economy. From view point of economy, if the length of
penstock required is short then one penstock each may be
provided to the turbines, however for longer penstocks a single
penstock or as few penstocks as possible may be used.
(c) Transportation facilities. The penstock size should be so
selected that it is easily transported from one place to another.
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22. Cont’…
Penstock materials and their suitability
 Reinforced concrete penstocks
 Wood-stave penstocks
 Steel penstocks
 High pressure penstocks
 Welded joints
 Penstocks are generally supported by concrete piers, although
they may he laid on or in the ground.
 Penstocks are sometimes covered to protect them from rock or
snow slides, prevent freezing, or eliminate expansion joints.
 Buried penstocks are subject to corrosion, which can be
eliminated or at least greatly reduced by cathodic protection
which prevents electrolysis from attacking the metal.
 Exposed penstocks last longer and are more accessible for
inspection and maintenance.
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23. Surge Tanks
 Surge tank or surge tower is a structure introduced in the system
in between the dam and power house, nearest to the power house
to provide better regulation of flow of water when the load on
the system fluctuates.
 A surge tank is a small reservoir or tank in which the water level
rises or falls to reduce the pressure swings so that they are not
transmitted in full to a closed circuit.
 The pipe between the surge tank and turbine is known as
penstock.
 In general a surge tank serves the following purposes :
 To reduce the distance between the free water surface and
turbine thereby reducing the water-hammer effect
 To serve as a supply tank to the turbine when the water in the
pipe is accelerating during increased load conditions and as a
storage tank when the water is decelerating during reduced load
conditions. 1/2/2023
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24. Types of surge tanks
The different types of surge tanks in use are
 Simple surge tank
 Inclined surge tank
 The expansion chamber and gallery type surge tank
 Restricted orifice surge tank
 Differential surge tank.
 A simple surge tank is a vertical stand pipe connected to the
penstock
 Surge tanks are built high enough so that water cannot overflow
even with a full load change on the turbine.
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25. Cont’…
 It is always desirable to place the surge tank on ground surface,
above the penstock line, at the point where the latter drops
rapidly to the power house as shown in Fig.
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26. Inclined surge tank
 When a surge tank is inclined to the horizontal its effective
water surface increases and therefore, lesser height surge tank is
required of the same diameter if it is inclined or lesser diameter
tank is required for the same height.
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27. Expansion chamber surge tank
 This type of a surge tank has an expansion tank at top and
expansion gallery at the bottom; these expansions limit the
extreme surges.
 The 'upper expansion chamber' must be above the maximum
reservoir level and 'bottom gallery' must be below the lowest
steady running level in the surge tank. Besides this the
intermediate shaft should have a stable minimum diameter.
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28. Restricted orifice surge tank
 It is also called throttled surge tank. The main object of
providing a throttle or restricted orifice is to create an
appreciable friction loss when the water is flowing to or from
the tank.
 When the load on the turbine is reduced, the surplus water
passes through the throttle and a retarding head equal to the
loss due to throttle is built up in the conduit.
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29. THANK YOU
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