Guidelines For Layout of Small Hydro Plants (Draft), AHEC Roorkee, India
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DRAFT FEB 07, 2008
STANDARDS / MANUALS / GUIDELINES
FOR SMALL HYDRO DEVELOPMENT
SPONSOR:
MINISTRY OF NEW AND RENEWABLE
ENERGY
GOVERNMENT OF INDIA
CIVIL WORKS
GUIDELINES FOR LAYOUT OF SMALL
HYDRO PLANTS
LEAD ORGANIZATION:
ALTERNATE HYDRO ENERGY CENTRE
INDIAN INSTITUTE OF TECHNOLOGY, ROORKEE
CONTENTS
S.No. TITLE Page No.
1. Guidelines for Layout of small hydro plants 1
1.1. Introduction 1
1.2. Guidelines for layout of shp 1
1.3. types of scheme 2
1.4. run – off – river scheme 2
1.5. canal falls schemes 2
1.6. toe of dam schemes 3
1.7. renovation of existing plants 4
1.8. layout methodology – general 6
1.8.1. Data collection 6
1.8.2. map studies 7
1.8.3. Field Visit 7
1.8.4. Mapping and site investigations 7
1.8.5. Conceptual Design 7
1.9. Layout of Run – off – river Schemes 8
1.9.1. Determination of plant flow capacity 8
1.9.2. Determination of FSL of Head Pond 8
1.9.3. Feeder Canal 9
1.9.4. Desilter 9
1.9.5.
Power Canal 9
1.9.6. Other Water Conduction Structures 9
1.9.7. Forebay Tank 10
1.9.8. Penstrock Intake 10
1.9.9. Penstock 10
1.9.10. Surge Tanks 12
2. Lowest Down Surge 13
3. Weight of Steel Surge Tank 13
3.1. Powerhouse and Tailrace 13
3.2. Layout of Canal Falls Schemes 13
3.3. Layout of Dan Toe Schemes 14
3.4. Determination of Capacity and Energy Benefits 14
3.5. Benefits and Economic Evolutions 14
3.6. RET Screen 14
3.7. Provision for Future Expansion 16
3.8. References 16
3.9. Examples of Project Layouts 17
AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Layout Of Small Hydro Plants /Feb 2008 1
CIVIL WORKS
Preamble
This part provides guidance on layout, hydraulic and structural design of civil
works and on the maintenance of civil structures and related hydro mechanical
equipment.
1 GUIDELINES FOR LAYOUT OF SMALL HYDRO PLANTS.
1.1 Introduction
The objective of this phase of study is to produce estimates of preliminary costs
and benefits of a scheme and to assess its economic viability. Often the work of
this phase is done with incomplete site data. If the findings of this phase show that
a scheme appears technically and economically feasible then more detailed pre-
feasibility and feasibility studies can be commissioned. The initial findings can be
useful in designing the scope of investigations needed to reliably evaluate the
scheme.
This section provides guidelines on the conceptual design of small hydro plants.
1.2 Guidelines for Layout of SHP
The following topographical features favour the development of economic
layouts:
a) Waterfalls
b) Rapids
c) Irrigation canal falls
d) Toe of dam locations
e) Canyons and narrow valleys
f) Major river bends
Small hydro plants are most often associated with features a) to d) and
infrequently with e) and f).
In layout studies (conceptual design) the engineer shall also take into account
other site specific conditions, as given in the following checklist.
Table 1.1 Check List on Site Conditions
Factors to consider:
• Climate
• Condition of main road to the area, weight and width limitations on bridges.
• Access to site and space for structures and site roads.
• Foundation conditions and slope stability
• Developable head
• Penstock/head length ratio
AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Layout Of Small Hydro Plants /Feb 2008 2
• Availability of construction materials (sand, aggregates, lumber and
impermeable fill, as required)
• Local services and skills availability
• High water levels and tail water and head pond flow rating curves
• Others
1.3 Types of schemes
The most common development schemes for Indian small hydro projects are of
the following types:
• Run-of-river
• Canal falls
• Toe of dam
• Renovation of existing plants
1.4 Run-of-River Schemes
A typical run-of-river project would comprise:
• Low diversion dam and intake (head works)
• Desilter
• Power canal / Power Tunnel
• Forebay tank / Surge Tank
• Penstock
• Powerhouse and tailrace
If the water carries a substantial sediment load (say more than 200 ppm on
average) a desilter would also be required. Preferably, the desilter would be built
as close to the intake as possible, but can be located anywhere along the water
conductor system where relatively flat land can be found. It should be noted that
the waterways upstream of the desilter must be designed for turbine plus flushing
flows and while downstream turbine flow alone is sufficient. Most often the water
conductor system will be a concrete masonry canal of rectangular cross section.
However, depending on site conditions, portions of the water conductor system
may have to be constructed as box culverts, tunnels, aqueducts, pipelines or
inverted siphons.
A typical example of a mini hydro scheme is shown in Figure 1.4.1 and an
example of a small run-of-river project is Figure at end of this Section.
1.5 Canal Falls Schemes
Canal falls are locations along an irrigation canal where the level of the canal is
stepped-down in a fall structure to better conform to ground elevations. Although
the developable heads available at such structures are often quite small (2.0 m to
5.0 m) the energy potentials are significant given the large flows available.
Almost all canal fall projects undertaken to date have been constructed many
AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Layout Of Small Hydro Plants /Feb 2008 3
years after the original canal project had been completed and were subject to the
following constraints:
• That the new powerhouse would be constructed without interfering (or
with minimum interference) of irrigation system day-to-day operations.
• That the new plant should not jeopardize the safety of the existing
structures.
A typical plant layout includes a bypass (power) canal, compact intake-power
house and tailrace canal rejoining the irrigation canal below the existing fall
structure. All efforts should be made to minimize costs while maintaining
efficient operation.
Innovative solutions include:
• Use of vertical axis semi-Kaplan units in a siphon elbow (used for heads
up to 4.0 m and unit capacities up to 500 kW). This approach provides
above water access to turbine runners, thus eliminating the need for very
costly intake and draft tube gates.
• Use of speed increasers to permit use of small low cost high speed
generators.
At other sites, more conventional bulb or Kaplan turbines layouts were selected.
As hydraulic losses have disproportionately high impacts on the economics of low
head developments, careful attention to hydraulic design is required to minimize
head losses at the canal entry, trashracks and flow restitution in the tailrace canal.
All canal fall projects must include provision for flow bypassing so that irrigation
flows can be maintained during periods when the plant may be out of service.
A typical example of this type of development is the Sirkhinda Mini Hydel.
Figure 2.1.3 shows the main features of this project.
1.6 Toe of Dam Schemes
A toe of dam project would comprise an intake and short penstock, powerhouse
and tailrace canal returning flow to a main irrigation canals or river. The intake
and penstock would normally be constructed in parallel to the outlet works, to
ensure that irrigation on water supply releases would not be interrupted during
periods when the plant might be out of service. The power plant intake and
penstock may be incorporated into the diversion works or spillway, as practical,
or constructed as a separate facility in an abutment. Typically, toe of dam projects
are located below storage reservoirs that would effectively trap sediment entering
the reservoir. Therefore sediment abrasion of turbine components would not be a
problem with this type of development. These plants are often subject to large
variation in head and flow and turbine selection must take this into account. These
conditions favour the use of Kaplan turbines. Depending on the operating rules of
the reservoir toe of dam reservoir may produce significant amounts of firm
energy, or only secondary energy.
AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Layout Of Small Hydro Plants /Feb 2008 4
A typical example of a toe of dam development is Dukwan SHP. Figure 2.1.4
shows the main features of this development.
1.7 Renovation of Existing Plants
There are many old hydro plants in India, where operating and maintenance costs
are increasing due to deterioration of aging equipment and structures. Also plant
efficiencies are decreasing due to wear of turbine parts. Renovation projects are
often initiated by the necessity of major equipment repairs such as runner
replacement or generator rewinding. At such times it is opportune to undertake a
complete refurbishment of the plant. Combining several renovation activities
together will reduce the cost of downtime and lost energy production, which
would be incurred if renovation was done piece-meal. This minimizes the cost of
lost production which is a significant factor in the economics of renovation
projects. In terms of economic parameters such as b/c ratio renovation projects are
often found to be very attractive.
These are three fundamental options to evaluate in a renovation project:
• Plant abandonment.
• Plant renovation
• Plant upgrading
A renovation project should start with a thorough condition assessment of the
plant including hydrology, civil structures, electrical and mechanical equipment.
Assessment of civil structures should include a re-evaluation of structural
stability, flood hydrology and spillway flow capacity. Deficiencies in civil works
should be identified and requirements for refurbishment defined. Condition
assessment of equipment should be done by qualified electrical and mechanical
engineers using approved testing methods to evaluate condition and performance.
Based on the findings of these condition assessments lists of items requiring
repair or replacement should be prepared and opportunities for upgrading
identified. It is customary to assign standard service lives to structures and
components mainly for the convenience of economic and financial analysis. In
reality some plant components can continue to perform satisfactorily well beyond
their conventional service life where site conditions are favourable and
maintenance work has been regularly performed. Therefore it might not be
necessary to replace some components simply because they have exceeded their
conventional service lives. Other items, notably electrical instrumentation and
switchgear, which could still be in good operating condition, may be considered
technologically obsolete because spare parts are no longer manufactured.
Replacement of these items with modern components should be assessed as part
of a renovation project.
With the above data in hand the scope of renovation should be evaluated by
comparative studies of selected development concepts (options). Such conceptual
AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Layout Of Small Hydro Plants /Feb 2008 5
design (layouts) should be developed in sufficient detail so that reliable capital
costs and benefits can be determined and the relative merits of each option
reliably evaluated.
The following paragraphs elaborate on the objectives of each type of option:
• Plant Abandonment
Abandonment might be the preferred choice where site conditions have
changed excessively over the life of a project or where renovation costs
are found to be excessive. For example, change in site conditions could
result from excessive flow diversion from upstream. Occasionally, a plant
may be abandoned in favour of a major redevelopment of the site as part
of a much larger project.
• Plant Renovation
The objective of plant renovation is to restore the plant to its original
condition. This improves plant reliability and extends service life. Civil
works are minimal in this option and are limited to necessary repairs to
restore structural integrity and function. Although the basic objectives of
this option would be achieved with replacement of turbines and generators
(if required) of the original designs; it may be worthwhile to consider new
runner designs for improved efficiency. If generator rewinds also required,
then new designs with improved insulation material and more copper
should also be considered. Options for modernization of switch gear,
protection and control should also be assessed.
Typical benefits from this option are:
- Recovered efficiency 5% - 5%
- Efficiency improvement turbine 3% - 5%
- Efficiency improvement generator 0.5% - 1%
- Increased capacity 6% - 15%
8.5%- 12% in energy.
8.5% - 15% in capacity.
• Plant upgrading
Plant upgrading usually implies substantial increases in plant output.
Upgrading could involve additional units in an extended power house or
development of a new powerhouse on the opposite bank or replacement of
existing units with larger units. These approaches all assume substantial
increases in power plant flows that would require additional civil works
above the necessary repairs as noted in the proceeding sub section. Unless
the original design included provisions for these expansions, execution of
the required civil works can become quite complicated as these works may
interfere with existing structures and / or ongoing plant operations –
AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Layout Of Small Hydro Plants /Feb 2008 6
introducing additional works and risks. Careful analysis and planning of
construction activities will therefore be necessary to minimize such risks.
Benefits from upgrading projects are very site specific but often can
double the output of the original project. An interesting example of an
upgrading project is Bluefish G.S. in NWT, Canada. Figure 2.1.4 shows
the main features of this project.
Further guidance on various aspects of plant renovation can be found in the
following references:
• Guide to Concrete Repair
U.S. Department of the Interior
Bureau of Reclamation
Technical Service Center (available on internet)
• Guidelines for Evaluating Aging Penstocks (manual) ASCE ca. 1995.
• IEA Guidelines on Methodology for Hydroelectric Francis Turbine
Upgrading.
IEA Guidelines on Methodology for Generator Upgrading.
IEA Guidelines on Methodology for Upgrading Controls.
All from the International Energy Agency – Paris
• Renovation, Modernization, Upgrading and Life Extension (RMU&LE) of
Hydro power Stations.
Manual Published by Central Board of Irrigation and Power. New Delhi.
• Civil Works for Hydroelectric Facilities: Guidelines for Extension
Upgrade, ASCE Hydropower Task Committee, 2007
1.8 Layout Methodology - General
Layout or conceptual design involves the identification of all practical alternatives
and the evaluation of such alternatives in order to determine the optimal
conceptual design. If the selected design appears economically viable then more
detailed feasibility studies would be undertaken in a later phase of studies. The
recommended layout methodology includes the following sequential steps:
• Data Collection
• Map studies
• Field Visit
• Mapping and site geotechnical investigations
• Conceptual design
• Economic evaluation
• Report on preliminary studies
1.8.1 Data Collection
All available maps and documents including: site or regional hydrology
data, previous planning studies, market surveys, aerial photos, geology
reports should be collected and reviewed.
AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Layout Of Small Hydro Plants /Feb 2008 7
1.8.2 Map studies
Potential development schemes should then be laid out on available
mapping for guidance during the field visit. It is further recommended that
an outline of preliminary studies report be made at this time and a check
list prepared before going into the field. This will help to establish which
important information is lacking in order to obtain it during the field visit.
1.8.3 Field Visit
The field visit provides an opportunity to obtain an appreciation of site
topography, flow regime, geology and access for roads and transmission
lines. From these on-site observations it is often possible to identify
practical locations for temporary facilities, head-works, desilting tank and
powerhouse and to decide the side of the river best suited for routing of
the waterways, preliminary access roads and T.L. routes. These locations,
their elevations and co-ordinates can be determined with portable GPS
equipment. It is also recommended that the inspection team include at last
three professionals: a hydrologist, a geologist and a hydropower engineer.
It is also recommended that the team include local representatives. Their
practical knowledge of the area and its people could be invaluable.
Typically, a field visit will require 1-3 days depending on the remoteness,
size and complexity of the site. Field visit should be supplemented with
photos and a field inspection report prepared.
1.8.4 Mapping and site investigations
The scope of the mapping and site investigation programs should be
prepared following the field visit. The extent of the mapping should be
sufficient to cover all alternatives envisaged and to allow for reasonable
adjustments (re-alignments) of structures, waterways, access roads and
T.L. routes. It is also recommended that surveyors also record ground
conditions on their maps, such as: grass land, sparse or heavy forest,
ephemeral on perennial streams, deep soil, broken rock or solid bed rock.
For small projects high head schemes extensive site investigations are
rarely required, but should at least include collection of sand and rock
samples to test for suitability for concrete production. On larger projects,
diamond drilling, geological mapping and (possibly) seismic surveys may
also be required, as recommended in Section 1.13 of the Standards.
1.8.5 Conceptual Design
In this activity preliminary designs and cost estimates are prepared for
each alternative and benefits evaluated. The relative merits of each
alternative are then be assessed by economic analysis to determine the best
alternative. Careful attention should be paid to the cost components with