2_1_civil Works- Guidelines for Layout of Small Hydro Plants

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


• 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


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.


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


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 –


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.


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


vary from one alternative to the other. Less attention is needed for determining the cost of common components, such as: access roads; since their values will not affect the outcomes of comparisons between alternatives. In this section preliminary design parameters are suggested to facilitate layout and sizing of project components. These preliminary parameters should later the refined in component optimization studies in detailed feasibility study or design phases, but such changes should be relatively minor and unlikely to change the choice of optimal alternative. Preliminary design is based on data developed in the above steps and hydrology studies performed in accordance with Section 1.4 of the Standards.

1.9 Layout of Run-of-River Schemes:

1.9.1 Determination of plant flow capacity

Plant flow capacity should be developed with reference to the flow duration curve (FDC) for the site. The following preliminary criteria are suggested: For isolated plants: QP = Q90% For grid connected plants: QP = Q35% Where: QP = plant flow capacity (m3/s).

QT% = flow equaled or exceeded T% of time.

1.9.2 Determination of FSL of Head Pond

Three types of intakes are suitable for low head diversions: lateral intake, trench intake or Tyrolean intake. Lateral intakes would be favoured on relatively narrow rivers and for medium to large flows (5m3/s and above). Trench intakes would be favoured in relatively wide plains rivers for plant flows up to about 20m3/s, at which point a lateral flow design should be considered. Tyrolean intakes would be favoured for mountain streams and for relatively small plant flows up to about 2 m3/s. Section 2.2.1 of the Standard provides rules on determination of diversion heads for each type of intake structure. For the lateral type the resulting FSL should be compared with the natural high water level, conventionally taken as the level for the mean annual flood (Q2). Also the MFL should be calculated for the design flood, normally Q100 for SHP (or Q10 for temporary type head-works of mini-hydro schemes). The need for spillway gates is determined considering the


elevation of the MFL and whether unacceptable upstream flooding upstream flooding would be caused with a simple overflow weir design.

1.9.3 Feeder Canal

Feeder canals transport sediment laden water from the intake to the desilter. They should be designed to carry 1.20Qp which provides 0.20 Qp flushing flow for desilter operation (assuming continuous flushing type). Preliminary canal dimensional design should be based on V = 1.5 m/s to ensure no sediment deposition (based on coarse sand, d = 2.0 mm). For flows up to 2.0 m3/s canals in masonry would be preferred, while for larger flow reinforced concrete should be considered.

1.9.4 Desilter

A continuous flushing hopper design with four hoppers is recommended, Preliminary design of the settling tank (parallel wall section) can be derived from the following formulae. For a design flow of Q (flushing flow plus plant flow): - Depth D = 1.30 Q (m)

- Specific Volume (Vs) = 50.7 Q (m3 per m3/s of flow). - Tank Volume (VT) = Vs.Q (m3) - Length (L) =

DVT

4 (m)

- Width (W) = 4L (m)

This design is based on excluding silt of 0.2 mm and larger. Four hoppers with depths of W/2 are also required below the rectangular tank bottom for flushing. Where practical a distribution weir is preferred at the entry to the tank, otherwise a transition section expanding at 6:1 will be required. At the outlet end a converging transition is also required, a straight sided section converging at 2:1 is satisfactory.

1.9.5 Power Canal

A design velocity of 1.5 m/s is recommended for preliminary design of the power canal. Choice of construction type would be the same as for feeder canals, as noted above.

1.9.6 Other Water Conductor Structures

Where topography is unfavourable other types of water conductor structures may be required. In such cases the engineer will have to develop more detailed layouts in accordance with the relevant standards and guidelines.


1.9.7 Forebay Tank

For projects, where water is conveyed by canals a forebay tank is normally required at the transition between canal and penstock to handle transient flows due to changes in plant operation and also to facilitate plant control for plants operating in water level control mode. For preliminary design the tank volume can be determined using the following formula: V= Qp ×120 (m3) The tank area would be calculated assuming a difference of 1.0m to 2.0m between the tank FSL (spillway crest) and minimum operating level.

1.9.8 Penstock Intake

The concrete volume of a typical penstock intake is approximately 15.QP m3 and net cost can be estimated as: C1 = 15.Qp.f1 Where: QP = plant flow (m3/s) f1 = unit price of reinforced concrete (Rs/m3)

C1 = cost of intake (Rupees). The penstock intake should be protected with trash racks but gates can be omitted for mini-hydro plants.

1.9.9 Penstock

Check head /length (H/L) ratio of the proposed penstock layout, if H/L > 5 a surge tank or turbine bypass valve may be required. Exceptions to these requirements are:

- Mini hydro plants with load controller. - High head plants with Pelton turbines

If H/L > 5, then calculate maximum length of penstock:

Lmax = 3.14 Hn. VTe (m)

Where: Hn= net head on turbine (m) Te = effective governor closure time, max = 6.0 secs V = flow velocity in penstock (m/s) [for penstocks with varying diameters Aequiv = L/ΣAi/Li and V = Q/ Aequiv]. If L< Lmax, no surge tank is required. The economic diameter of a penstock can be estimated as below:


D = 3.55 25.02

2 ⎟⎟⎠

⎞⎜⎜⎝

⎛gHQ Sarkaria’s equation

or

D = 0.3

.4 Qπ

based on V = 3.0 m/s

Use the lesser of the two values. Weight of Penstock Steel: An approximate estimate of steel penstock weight can be calculated as below: Input data:

- H = max head at turbine with normal waterhammer (m) (Use 1.3Ho for Francis, 1.4Ho for Kaplan & 1.15Ho for Pelton) - D = diameter of penstock (m) - L = length of penstock

Calculate

3min 101D)1.25(9.0t ×+= m

m0.0015HD0.0000272tmax += If minmaxt t≤ Wt = 24.5 tmin.D.L tonnes If tmax > tmin

⎟⎟⎠

⎞⎜⎜⎝

⎛−⎟

⎠⎞

⎜⎝⎛ +

+⎟⎟⎠

⎞⎜⎜⎝

⎛=

max

minmaxmin

max

minmin t

t1.D.L.

2tt

24.5tt

.D.L.t24.5Wt tonnes

For surface penstocks estimate volume of concrete saddles as: Vf = 3.5 (L.D2) 0.82 and Cost (C2) = Vf. f2 Where: L = slope length of penstock (m) D = diameter of penstock (m) Vf = concrete volume, footings (m3)

f2 = unit price of footing concrete (Rs/m3) C2 = estimated cost of footing (Rupees)


The volume of anchor block concrete is of the same order of magnitude as concrete saddles; therefore assume cost of anchor blocks as 66% cost of saddles (or derive a more exact cost from detailed layouts).

1.9.10 Surge tanks

Surge tanks are required to protect long penstocks from excessive water hammer pressure rise, to control excessive generator runaway speeds and to contribute to system speed regulation. Alternatives to surge tanks providing some of the benefits of surge tanks, include:

- addition of extra machine inertia (typically by adding a flywheel to a horizontal axis unit or extra mass to a vertical axis generator).

- installing turbine bypass valves. - pressure relief devices.

As surge tanks are expensive all options should be evaluated. Section 2.2.6 of this Standard provides guidelines for this task. A preliminary design methodology for surge tanks is outlined below. It is conservative.

1.9.10.1 Cross-section area of surge tank (As) = 02

6.1gcH

AL (m2)

- Where : A = cross section area of upstream pipe (m2) L = length of pipe, surge tank to reservoir (m) c = head loss factor as hL= c.V2 (m-1.s2) H0= steady state head on turbine (m)

1.9.10.2 Highest up-surge: In order to dimension the surge tanks it is also necessary to know the maximum and minimum water levels that can be expected. An approximate method is shown below that is based on Parmakian’s method for balanced design (Parmakian – 1960). This method provides equations relating the following parameters from which the maximum and minimum surge levels can be calculated:

Q0 = initial steady state flow (m3/s) As = cross-section area of surge tank (m2) g = acceleration due to gravity (= 9.8 ms-2) L = length of pipeline between forebay reservoir and surge tank (m) A = cross section area of pipeline (m2) SA = upswing (m) SB = downswing (m) H0 = steady state water level in surge tank (m) Hs = static water level in surge tank (m) Hf and bo as defined below:


For maximum upsurge calculate:

Hf = pipe friction loss + minor losses + g

Vo

2

2

ALgA

QH

b s

o

fo /

.=

foA HbS .05.1 89.0−= Max. W.L. = Ho - Hf + SA 2 Lowest down surge: For lowest downswing calculate

Hf = pipe friction losses + minor losses + g

Ve2

2

(where Qe = flow demanded by turbine)

ALgA

QH

b S

e

fo /

.=

fB SbS .88.0 91.00−=

Minimum W.L. in surge tank = Hs - Hf - SB 3 Weight of steel surge tank (WS):

Ws = 1.29 x 10-4 x (HV) 0.96 (kg) H = Height above c/l of penstock to centroid of tank (m) V = Volume of tank cylinder (m3)

3.1 Powerhouse and Tailrace

Preliminary powerhouse layout requires the selection of appropriate generating equipment and estimation of the main powerhouse dimensions. Preliminary guidelines on unit selection and basic layout dimensions can be obtained from IS 12800: Guidelines for Selection of Hydraulic Turbine, Preliminary Dimensioning and Layout of Hydroelectric Power Houses. Using these basic dimensions, preliminary powerhouse layouts can be prepared. Alternatively, for preliminary analysis, powerhouse cost estimates by a parametric estimating technique are satisfactory. The RETScreen Model can be used to obtain preliminary powerhouse cost estimates, as explained in Sub-Section 3.6 of this Standard.

3.2 Layout of Canal Falls Schemes There are rarely more than two alternatives for development depending on which side of the existing canal the diversion canal and powerhouse would be located. Practical considerations regarding foundation conditions, access and the like will probably decide the optimal arrangement. Coffer dams are not usually needed as interconnecting canals can usually be build


during periods when the canal would be out of service for annual maintenance. Attention must also be paid to hydraulic design to minimize head losses. Acceleration of flow velocity through the entry is acceptable if economically justified and compatible with flow conditions at the power plant intake. Deceleration of flow velocity should be avoided. Layout concepts should be based on successful designs of similar plants. Central Board for Irrigation and Power (CBIP, 2003) gives an inventory of Indian hydropower plants with salient data and drawings.

3.3 Layout of Dam Toe Schemes. As for plants at canal falls, practical consideration of site characteristics, foundations, access and the like will probably determine the optimal arrangement. Occasionally original designs will include provision for addition of a power plant. Layout concepts should be based on successful designs of similar projects. Design of cofferdams and other protective works must be done with equal care as these works form an integral part of a successful project. Examples of successful designs can be found in CBIP (2003).

3.4 Determination of Capacity and Energy Benefits.

For run-of-river hydro schemes average energy benefits are determined by integration of the project flow duration curve (FDC) using the net head appropriate for each flow class. For isolated or stand alone projects firm energy is of greater interest. Indian practice is to base firm energy determinations on the Q90% flow from the FDC. For this exercise it is convenient to express hydraulic losses as a function of Q2. Normally, maximum head loss is normally found to be between 2% and 10% of gross head. Energy output should be expressed in mean kWh per year. Firm capacity should be calculated based on the capacity that can be produced with Q90%. Firm capacity, firm energy and mean energy should all be referenced to the transmission, or distribution line, voltage as appropriate.

3.5 Benefits and Economic Evolutions The determination of benefits and economic evolution should be carried out in accordance with Sections 1.4, 1.6 and 1.7 of the Standard. For isolated SHP the capacity providing the least cost of energy should be selected. For grid connected plants the optimum capacity should be based on benefit-cost analysis using appropriate incremental costs for energy and capacity. These values should be selected in consultation with the responsible State or Central Government authority.

3.6 RET Screen

RET Screen is a computer model developed by the Government of Canada, Department of Natural Resources and available freely over the internet at www.retscreen.net. The model is available in several languages, including Hindi. The purpose of the model is to compute costs and benefits, including greenhouse gas analysis, for small scale run-of-river


projects. While originally intended as a tool for preliminary studies utilizing mainly map data, the latest version now allows the engineer to enter work quantities and unit costs against a comprehensive list of work items.

The program is setup in Excel and comprises four screens, as below: 3.6.1 Energy Data Model Input Data: H, Qp, Qr, ΣHL, η gen, transformer losses and parasitic losses and hydrologic & equipment parameters as calculated in Screens 2 and 3. Output: Annual energy production. 3.6.2 Hydrology Input Data: Flow duration curve (FDC). Output: FDC and load duration curve (LDC) in tabular and graphic formats. 3.6.3 Equipment Input : Type of turbine. Output : Estimated turbine efficiency curve. The program calculates the energy benefits which are reported in Screen 1, using hydrology and equipment data from Screens 2 and 3.

3.6.4 Cost Analysis

Two options are offered: detailed cost analysis or formula costs. Input: Choose the method that is most suitable for cost analysis (detailed or formula) then select economic parameters in accordance with Section 1.7 of the Standard.

If the detailed analysis is chosen, the engineer will have to provide quantities and units costs for the list of work items contained in the program. The list allows inclusion of additional items one for each division of the work list.

If the formula analysis method is chosen cost components are determined from parametric equations for each structure. Data comprise characteristic parameters (geometry, flow or capacity) for each structure. Overall data requirements are much less in this option. For preliminary design and planning studies the utility of this option is enhanced if the model is first bench marked (on calibrated) against recent projects and escalation factors and main unit prices adjusted to fit. The currency for all cost and financial calculations are input in this screen, along with the applicable conversion rate Rs per Canadian $ 1.00.


Output: Capital cost estimate

3.6.5 Financial Summary Input : Financial parameters Output : Project costs and savings

Results of financial analyses Cost of power.

3.7 Provision for Future Expansion

The engineer should think about the possibility of future expansion and consider providing features that would facilitate such work in the future. Such provisions could include addition of a branch in a penstock, pre-excavation of the foundation of a future unit and the like. An appropriate structural addition could greatly simplify expansion of the plant in the future with significant savings in cost and schedule.

3.8 References

Indian Standards Cited IS 12800 (Part 3) Guidelines for Selection of Hydraulic Turbine, Preliminary Dimensioning and Layout of Surface Hydroelectric Power Houses. Other References Waterhammer Analysis J. Parmakian, Dover Publishers (1963) Hydroelectric Power Stations in Operation in India, CBIP (2003) RET Screen International: Clean Energy Project Analysis Software Natural Resources Canada Ottawa Website: www.retscreen.net


3.9 Examples of Project Layouts:

FIGURE: 1.4.1 KEDERNATH MINI HYDEL

2_1_civil Works- Guidelines for Layout of Small Hydro Plants

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