Water Conductor Elements

Elements of Water Conductor System
 Pressure Tunnels
 A typical section through a tunnel is shown in Fig.
 The initial portion of the tunnel from the intake up to the
Surge-Tank is termed as the Head Race Tunnel (HRT) and
beyond that it houses the penstock or steel-conduits, which
sustains a larger pressure than the HRT.

Intake Structure
 An intake is provided at the mouth of a water
conveyance system for a hydropower project.
 It is designed such that the following points are
complied, as far as possible:
 There should be minimum head loss as water enters
from the reservoir behind a dam or the pool behind a
barrage into the water conducting system.
 There should not be any formation of vortices that
could draw air into the water conducting system.
 There should be minimum entry of sediment into the
water conducting system.
 Floating material should not enter the water
conducting system.

Elements of intake
1. Trash rack and supporting structure.
2. Bell mouth entrance.
3. Gates with air vents.
4. Log/Trash boom.

Trash rack and screen
• A trash rack is a wooden or metal structure, that
prevents water-borne debris (such as logs, boats,
animals, masses of cut waterweed, etc.) from entering
the intake of water conveyance.
• This protects penstock, and sluice gates from
destruction and blockage due to debris, logs etc.

Trash Rack
Trash rack Trash rack

Removing or cleaning process to trash rack

Gates
It controls/regulates the entry of water into the intake.

 ICE,LOG,AND TRASH BOOMS
Floating boom use to perform one or more of the
following functions
1. Deflection of logs and trash from the intake
screens.
2. Deflection of ice away from the intake.
3. Prevention of the boats form being carried into
the intake

Intake Structure
 The position and location of an intake in a
hydropower project would generally depend
upon the type of hydropower development, that
is, whether the project is of run-of-river type or
storage type.
 Therefore, intake structure can be classified as:
 Run-of-river type intake
 Reservoir type intakes
 Intake also depends upon whether water conveyed
through canal (power channel) or tunnel conduit

Intake Structure
 Intakes adjacent to a diversion structure like a
barrage.
 Here, an intake for a tunnel is placed upstream of
the diversion structure to draw water from the pool

Intake Structure
 For a canal intake, the head regulator resembles that
of an irrigation canal intake.
 When the canal conveying water, also called the
power canal, it leads to a Forebay before leading to
the turbine unit, which is important element.

Intake Structure
 Intakes for concrete dams are located on the
upstream face of the dam.
 The face of the intake is rectangular and is reduced
to a smaller rectangular section through a transitory
shape known as the bell-mouth.
 From the smaller rectangular section, another
transition is provided to change the shape to
circular.

Intake Structure
 Intakes for embankment dams are usually in the
form of a conduit, which is laid below the dam and
are provided in the form of a tower
 A tower type intake is constructed where there is a
wide variation of the water level in the reservoir.

Intake Structure
 The choice and location of the intake structure
depends upon the following factors.
 Type of development, that is, run-of-the-river or
storage dam project;
 Location of power house and the dam ;
 Type of water conductor system, that is, tunnel,
canal or penstock;
 Topographical features of area;
 The intake can often be located so as to enable it to
be constructed before the level of the reservoir is
raised.

Water Conductor System
 After flowing through the intake structure, the
water must pass through the water conveyance
system may be either of closed conduit type,
(tunnel off-taking from upstream of the river
diversion) or could be open-channels.

 Open channels
 These are usually lined canals to reduce water loss
through seepage as well as to minimize friction loss.
 The design of canals for hydropower water
conveyance follows the same rules as for rigid bed
irrigation channels, and are usually termed as
power canals.
 A power canal that off-takes from a diversion
structure has to flow along the hill slope

 Open channels
 These are usually lined canals to reduce water loss
through seepage as well as to minimize friction loss.
 The design of canals for hydropower water
conveyance follows the same rules as for rigid bed
irrigation channels, and are usually termed as power
canals.
 A power canal that off-takes from a diversion
structure has to flow along the hill slope

 Open channels
 A cross section of the canal would show that there
would usually be high ground on one bank and
falling ground on the other .
 It is important to stabilize the uphill cut-slope with
some kind of protection in order to prevent fallout
of loose blocks of stone into the canal.

 Open channels
 The power canal ends at a forebay, which is broadened
to act as a small reservoir.
 From the forebay, intakes direct the water into the
penstocks.
 There usually is a bye-pass channel which acts as a
spillway to pass on excess water in case of a valve
closure in the turbine of the hydropower generating
unit.
 If such an escape channel is not provided, there are
chances that under sudden closure of the valves of the
turbines, surge waves move up the power canal.
 Hence, sufficient free board has to be provided for the
canals.

 Open channels
 Forbay
 A forebay is an artificial pool of water located
before and connected with penstocks
 Provided in case of run-off- river plants
 The major use of forebay is to
 distribution of flow of water in to penstocks ,
 store water which is rejected by hydropower plant,
 Containing a trash rack and bye-pass channel.

Forebay connectingwith penstock and Containing a
trash rack and bye-pass channel

 A typical section through a tunnel is shown in Fig.
 The initial portion of the tunnel from the intake up to the
Surge-Tank is termed as the Head Race Tunnel (HRT) and
beyond that it houses the penstock or steel-conduits, which
sustains a larger pressure than the HRT.

 The HRT may either be unlined (in case of quite good quality
rocks) or may be lined with concrete.
 The surge tank is provided to absorb any surge of water that
could be generated during a sudden closure of valve at the
turbine end.
 Normally, the water level in the surge tank would be
marginally lower than that at the intake and the difference of
levels depends upon the friction loss in the HRT.
 Thus, when the HRT runs full, it is subjected to a much low
pressure compared to the penstock.

 The layout is usually governed by the geological features of
the surrounding hills.
 Complicated geological conditions and extraordinary
geological occurrences such as intra-thrust zones, very wide
shear zones, geothermal zones of high temperature, cold/hot
water springs, water charged rock masses, intrusions, fault
planes, etc. should preferably be avoided.
 The Bureau of Indian Standards code IS: 4880-1976 “Code of
practice for design of tunnels conveying water” (Parts 1 to 4)
provide guidelines for design of a tunnel under various
situations.
 Sound, homogeneous isotropic and solid rock formations are
the most suitable for tunneling work.

 Penstock
 A penstock is one of the parts of conveyance system that
construct from a steel or reinforced concrete to resist high
pressure in the water conveyance system
 It may take off directly from behind a dam, from a forebay, or
from the surge tank end of a head race tunnel

 Penstock
 It’s function is conveying water from forbay or surge tank to
the turbine in the power house and it help to increase the
kinetic energy of water that comes from the end of head race.
 A penstock is subjected to very high pressure and its design
is similar to that for pressure vessels and tanks.
 However, sudden pressure rise due to valve closure of
turbines during sudden load rejection in the electric grid
necessitates that penstocks be designed for such water
hammer pressures as well.

 Penstock
 Since penstocks convey water to the turbines and form a part
of the hydropower water conveyance system, it is necessary
that they provide the least possible loss of energy head to the
flowing water.
 According to the Bureau of Indian Standards code IS: 11625-
1986 “Criteria for hydraulic design of penstocks”, the
following losses may be expected for a penstock:
 a. Head loss at trash rock
 b. Head loss at intake entrance
 c. Friction losses, and
 d. Other losses as at bends, bifurcations, transitions, values, etc.

 Penstock
 Based on the above losses, the diameter of the penstock
pipes have to be fixed, such that it results in an overall
economy.
 This is because if the diameter of a penstock is increased,
for example, the friction losses reduce resulting in a higher
head at turbine and consequent generations of more power.
 But this, at the same time, increases the cost of the
penstock.
 This leads to the concept of Economic Diameter of
Penstock which is one such that the annual cost, including
cost of power lost due to friction and charges of
construction, maintenance, operation, etc. is the
minimum.

 Penstock
 Types
 Buried penstocks or Embedded penstocks
 Exposed penstocks
1. Buried penstocks
2. Exposed penstocks

 Penstock
 Buried penstocks
 are supported continuously on the soil at the bottom of a
trench backfilled after placing the pipe.
 The thickness of the cover over the pipe should be about
1.o to 1.2 m.

 Penstock
 Merits
 The soil cover protects the penstock against effect of
temperature variations,
 It protects the conveyed water against freezing.
 Buried pipes do not spoil the landscape.
 They are safer against rock slides, avalanches and falling
trees.

 Penstock
 Demerits
 The inspection and faults cannot be determined easily.
 It’s installation expensive Especially For large diameters
and rocky soils.
 On steep hillsides, especially if the friction coefficient of
the soil is low, such pipes may slide.
 Maintenance and repair of the pipe is difficult.

 Penstock
 Exposed penstocks:
 are installed above the terrain surface and supported on piers
(briefly called supports or saddles).
 Consequently, there is no contact between the terrain and the
pipe itself, and the support is not continuous but confined piers
 Merits
 The soil cover protects the penstock against effect of
temperature variations,
 It protects the conveyed water against freezing. Buried pipes
do not spoil the landscape.
 They are safer against rock slides, avalanches and falling trees.

 Penstock
 Merits
 The possibility of continuous and adequate inspection
during operation.
 Its installation is less expensive in case of large diameters
of rocky terrain.
 Safety against sliding may be ensured by properly
designed anchorages.
 Such pipes are readily accessible and maintenance and
repair operations can be carried out easily

 Penstock
 Demerits
 Full exposure to external variation in temperature.
 The water conveyed may freeze.
 Owing to the spacing of supports and anchorages
significant longitudinal stresses may develop especially in
pipes of large diameters

Buried Penstocks Surface Penstocks
1. Protection against
temperature effect
1. Subjected to temperature
variations
2. Landscape does not get
affected
2. Landscape becomes
scared with the Penstocks
presence
3. Less accessible for
inspection
3. Easily accessible for
inspection
4. Greater expenses for large
diameter penstocks in rocky soil
4. Economical under such
circumstances
5. Does not require separate
support. Does not require
expansion joints
5. Requires anchorages for
support necessitating in
expansion joints

The following are some major factors that must be considered
in selecting a penstock route.
 Accessibility:
o The route should be accessible to personnel and
equipment required for pipe installation, inspection and
maintenance.
o In those areas where equipment access is difficult or
impossible; installation and maintenance must be
performed manually.
 Soil Conditions:
o Soils along the pipeline should be examined to identify
rock outcroppings, soft or unstable soils or other
characteristics that would interfere with penstock
installation or damage the penstock.

• Natural or Man-Made Obstructions:
• These include trees, roadways, buildings, stream
crossings, and other features that require special care.
• Gradient:
• The penstock is best routed to take advantage of the
natural downward gradient.
• If the line cannot be located so as to have a constant
downward gradient, an air relief valve or equivalent
device is required at every local high point, and a drain
valve is required at every local low point.

 Penstock
 Penstock Alignment
 To determine the most economical alignment of a
pipeline, the designer must investigate the site and make
various layouts on topographic maps.
 He must then estimate material quantities for each layout
and evaluate its constructability.
 When making the layouts, the penstock should be located
on stable foundation sites such as along a ridge or a bench
that has been cut into the mountainside, avoiding of
troublesome sites such as underground water courses,
landfill, fault zones and potential slide areas is quite
important.

 Penstock
 To minimize costly anchors and costly pipe transition
sections, vertical bends, horizontal bends and changes in
diameter should be combined in a way to have them at the
same location.
 Selection of the penstock alignment at site should be
base on the following criteria.

 Penstock
 1. Fore bay or surge tank location
 The penstock starts at the fore bay or surge tank, and its
location should be chosen to optimize the lengths of headrace
and penstock whilst achieving the required power output from
the scheme.
 Penstock pipe is generally more expensive than headrace canal
or tunnel therefore in most cases the fore bay or surge tank
location should be chosen to give the minimum penstock
length.
 However, sometimes a longer penstock may be economic to
avoid the need for the headrace to cross an unstable slope.

 Penstock
 2. Practical ground slope
 An ideal ground slope for the penstock alignment is between
1:1 and 1:2(V:H).
 The flatter the ground slope the less economic is the penstock
since a longer pipe length is required for a lower head.
 Although a steep slope minimizes the penstock length, it will be
difficult to manually lay the penstock, construct support piers
and anchor blocks if the slope is greater than 1:1.
 Therefore, for penstock alignments on slopes steeper than 1:1,
the added site installation cost may outweigh the savings made
on the pipe costs..

 Penstock
 3. Minimum number of bends
 Bends increase the head loss and require additional
anchor blocks.
 Therefore the selected alignment should be as straight as
possible, both in plan and elevation.
 Note that small bends can be avoided by varying the
support pier heights for the exposed section and the
trench depth for the buried section.

 Penstock
 4. Space for powerhouse area
 The chosen alignment should be such that it is possible to
construct a powerhouse at the end of the penstock.
 A river terrace well above the flood level is ideal for the
powerhouse area.
 A route that is otherwise suitable for the penstock
alignment but does not allow for the construction of the
power house is inappropriate.

 Penstock
 5. Stability
 Since the penstock alignment is on steep ground slopes
and the pipe is under pressure, it is important for the
alignment to be on stable ground.
 Any ground movement can damage the pipe, support
piers and anchor blocks and in case of pipe bursts
unstable slopes will cause further erosion and landslides.

 Penstock
 6. Other site specific conditions
 Apart from the above criteria, there may be other site
specific conditions that dictate the penstock alignment.
 For example, if the alignment crosses a local trail, road,
canal, this section should either be buried or high enough
above the ground such that people and cattle can walk
underneath.

 Penstock - Accessories
 Bends
 Depending on topography, the alignment of the penstock
is often required to be changed, in direction, to obtain the
most economical profile.

 Reducer piece
 In the case of very long penstocks, it is often necessary to
reduce the diameter of the pipe as the head on the pipe
increases.
 This reduction from one diameter to another should be
effected gradually by introducing a special pipe piece called
reducer piece.

 Supports
 In the case of very long penstocks, it is often necessary to
reduce the diameter of the pipe as the head on the pipe
increases.
 This reduction from one diameter to another should be
effected gradually by introducing a special pipe piece called
reducer piece.

 Expansion joints
 are installed in exposed penstocks to prevent longitudinal
expansion or contraction when changes in temperature
occur.

Water Conductor Elements

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