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THE WATT COMMITTEE ON ENERGYREPORT NUMBER 15

SMALL-SCALE HYDRO-POWER

Papers presented at the Sixteenth Consultative Council meeting of the WattCommittee on Energy, London, 5 June 1984

The Watt Committee on Energy Ltd

A Company limited by guarantee: Reg. in England No.1350046

Charity Commissioners Registration No. 279087MARCH 1985


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Contents

Members of the Watt Committee v

Members of Watt Committee Working Group onSmall-Scale Hydro-Power

vii

Foreword ix

Introduction xi

Section 1 Potential for small-scale hydro-power in the UnitedKingdomE.M.Wilson

1

Section 2 Hydro-electric plant and equipmentJ.TaylorC.P.Strongman

8

Section 3 Civil engineering aspectsN.A.Armstrong

37

Section 4 Institutional barriersE.C.ReedD.J.HintonA.T.Chenhall

48

Section 5 Economics of small public and private schemesA.T.ChenhallR.W.Horner

57

Section 6 Conclusions and recommendations

J.V.CorneyH.W.Baker

78

Appendix 1 Sixteenth Consultative Council meeting of the WattCommittee on Energy

81

Appendix 2 Government grants and funding availableP.J.Fenwick

83

Appendix 3 Use of water for milling or power generation:circumstances in which a licence is required

86

Appendix 4 National Association of Water Power Users: Paperfor the Watt Committee

93


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Appendix 5 Abbreviations 99

THE WATT COMMITTEE ON ENERGY

The Watt Committee on Energy 102

Policy

Members of Executive, March 1985

Recent Watt Committee Reports

102

103103


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Member Institutions of the Watt Committeeon Energy

March 1985

* British Association for the Advancement of ScienceBritish Ceramic Society* British Nuclear Energy SocietyBritish Wind Energy Association* Chartered Institute of Building* Chartered Institution of Building Services* Chartered Institute of Transport* Combustion Institute (British Section)* Geological Society of London* Hotel Catering and Institutional Management Association* Institute of BiologyInstitute of British FoundrymenInstitute of Ceramics* Institute of Chartered Foresters* Institute of Cost and Management Accountants* Institute of Energy* Institute of Home Economics* Institute of Hospital EngineeringInstitute of Internal Auditors (United Kingdom Chapter)

Institute of Management Services* Institute of Marine EngineersInstitute of Mathematics and its Applications* Institute of Metals* Institute of Petroleum* Institute of Physics* Institute of Purchasing and Supply* Institute of RefrigerationInstitute of Wastes Management

* Institution of Agricultural Engineers* Institution of Chemical Engineers* Institution of Civil Engineers* Institution of Electrical and Electronics Incorporated Engineers


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* Institution of Electrical Engineers* Institution of Electronic and Radio EngineersInstitution of Engineering Designers* Institution of Gas EngineersInstitution of Geologists* Institution of Mechanical Engineers* Institution of Mining and MetallurgyInstitution of Mining Engineers* Institution of Nuclear Engineers* Institution of Plant Engineers* Institution of Production Engineers* Institution of Public Health EngineersInstitution of Structural Engineers* Institution of Water Engineers and Scientists* International Solar Energy SocietyU.K. SectionOperational Research Society* Plastics and Rubber Institute* Royal Aeronautical Society* Royal Geographical Society* Royal Institute of British Architects* Royal Institution* Royal Institution of Chartered Surveyors* Royal Institution of Naval Architects* Royal Meteorological Society* Royal Society of Arts* Royal Society of Chemistry* Royal Town Planning Institute* Society of Business EconomistsSociety of Chemical Industry* Society of Dyers and ColouristsTextile Institute

* Denotes present and past members of The Watt Committee Executive

vi


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Members of Small-Scale Hydro-PowerWorking Group

J.V.Corney Institution of Civil Engineers, ChairmanN.A.Armstrong Institution of Electrical Engineers and Institution of

Mechanical EngineersH.W.Baker Institution of Civil EngineersA.T.Chenhall Institution of Electrical EngineersD.J.Hinton Institution of Civil EngineersR.W.Horner Institution of Public Health EngineersM.J.Kenn Institution of Mechanical EngineersE.C.Reed Institution of Water Engineers and ScientistsJ.Taylor Institution of Electrical EngineersProf E.M.Wilson Institution of Civil Engineers


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Acknowledgements

Commander G.C.Chapman, Mr J.A.Crabtree and Mr O.M.Goring attendedseveral meetings of the working group as representatives of the NationalAssociation of Water Power Users.

The Watt Committee working group on Small-Scale Hydro-Power is indebtedto many individuals and organisations in the United Kingdom from whominformation and comments were obtained in the course of this project, includingthe Central Electricity Generating Board, North of Scotland Hydro-ElectricBoard, South of Scotland Electricity Board, regional Water Authorities and (inScotland) regional councils and River Purification Boards.

The Watt Committee on Energy acknowledges with thanks financialassistance by the Department of Energy, which helped to defray the costs of theproceedings of the working group, and the advice given by Dr P.J.Fenwick of that Department.

NoteThe data included in this Report were correct, to the best of the authors

knowledge and belief, in January 1985.


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Foreword

At any moment in time the Watt Committee has four or five working parties,each tackling a specific project. Those under discussion at the meeting of theWatt Committee Executive of 24th January 1985 were technician education,waste disposal in the energy industry, the second phase of our study of acid rainand passive solar building design. Two other projects awaited firm proposals,and a further two were temporarily suspended because they would be more realisticat a later date.

The present Report on Small-Scale Hydro-Power contrasts strongly with its twoimmediate predecessors, which dealt with nuclear energy and acid rainrespectively. * It shares with them, however, the desire to clarify what at themoment could hold up development. Our only previous report devoted entirely torenewable energy sources was No. 5 Energy from the Biomass . Reports No. 1and, to a less extent, No. 2 include sections on renewable sources; Report No. 4

Energy Development and Land in the United Kingdom contains two colouredmaps showing alternative source distribution in the United Kingdom andsuggests locations for wind, solar, wave, tidal and geothermal installations.

Discussions with a number of individuals about small hydro-electricgenerating capacity suggested that it was something of a Cinderella in that it wasunlikely to save much fossil fuel, and the cost per kilowatt could vary greatly

with the site and with the amount of outside help that would be required.Furthermore, there was no simple statement of the legal obligations.Like windmills (now elevated to aero-generators), small hydro-power has

suffered a long period of neglect illustrated by idle water-mills and mill-pondsused to supply fish rather than energy. A great deal of money has been spent onaero-generator design and a full-scale unit is under construction in the OrkneyIslands. If it comes up to expectations we shall see more schemes being built andused to save energy. The same should be true of hydro-power.

To add to this Foreword would mean drawing on the Report itself. I end,

therefore, with my personal thanks and those of the Executive to the numerous


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February 1985

J.H.ChestersChairman, The Watt Committee on Energy

* Particulars of previous Reports of the Watt Committee on Energy are given on pages 6162.

x

people who have given information, time and voluntary effort to add to ourunderstanding of the problems and the wider potential of small-scale hydro-power.


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Introduction

Despite the abundance of sites in the United Kingdom where small-scale hydro-power could be exploited, only a very small proportion of such potential is atpresent developed.

The Watt Committee on Energy was concerned at this lack of exploitation of avaluable resource and therefore decided to establish a working group to examinethe potential for development of further small-scale hydro-power as a usefuladdition to the energy resources of the United Kingdom. Its object was toidentify obstacles which may have inhibited development in the past and to makesuggestions for further study/action, with the eventual objective of helping toovercome the main obstacles and stimulate new schemes.

The working group was free to make its own definition of what was impliedby small-scale, and decided, in broad terms, that this should be any resourcebelow the size which the electricity boards had themselves considered worthdeveloping. In electrical terms we considered this to be from 5 to 5000kW.

We also decided, in order to limit the field of our study, that we would notinclude wave or tidal power, as these could properly form the subject of separatestudies. The papers forming this Report have been prepared by various membersof the working group and explore the potential for small-scale hydro-powerdevelopment in the whole of the United Kingdom. Topics covered include the

technical problems and legal, institutional, environmental and economic aspectswhich may have inhibited development in the past.The working group has been greatly helped and encouraged by the information

and assistance provided by members of the National Association of Water PowerUsers who have direct experience of constructing and operating small privateschemes. The number and variety of such schemes provide concrete evidence of the practicability of such development. The members of this Association areenthusiasts and have for the most part constructed and operated their schemesthemselves. Whilst clearly beneficial to their owners as they stand, they would

not all necessarily satisfy current economic criteria.Our studies have been purposely limited to developments in the UnitedKingdom, but many aspects will be equally applicable to developing countries,particularly where a public electricity supply is not available in the vicinity and


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the choice lies between hydro-electricity or, as an alternative, diesel generationwith high-cost fuel. The papers in general deal with water power for thegeneration of electricity, as it is in this form that it is easiest to assess its value asa power source; however, where an alternative use for the power exists it may besimpler to harness the power for such use, as was done in the past, rather than touse it for electricity generation.

The technology involved in the development of water power is not new, butthere are few people who have experience of both the engineering and the legalaspects, which are complex and varied. It is the hope of the working group that,by bringing together these subjects in one report, the problems facing potentialdevelopers of hydro-power will become better understood and many moresuccessful schemes will result.

J.V.CorneyChairman, Watt Committee Working Group on Small-Scale Hydro-Power

xii


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THE WATT COMMITTEE ON ENERGY

REPORT NUMBER 15

Section 1Potential for small-scale hydro-power in the

United KingdomE.M.Wilson

Department of Civil Engineering

University of Salford

Salford

Potential for Small-Scale Hydro-Power in the United Kingdom

1.1Introduction

The United Kingdom is not a country rich in hydro-electric resources. Only inScotland and Wales are there mountains and rainfall on a scale large enough tooffer opportunities for hydro-electric development of tens of megawatts.However, over the whole country there are hundreds of sites where modestamounts of hydro-electric energy could be generated, at powers measured in tensof kilowatts.

The problem of assessing potential requires, first, some arbitrary definition of what small-scale means, since many of the surveys made in the past haveconsidered schemes only if their power capacity exceeded fixed values,frequently in megawatts. So far as this paper is concerned, small-scale meansfrom 5 to 5000kW. An arbitrary sub-division can be made to mini- and micro-hydro, with capacities above and below 500kW respectively.

During the last five years several studies have been made of small-scale hydro-power in various parts of the U.K. These have supplemented many previousinvestigations: for example, there have been at least six sets of estimates of Scottish hydro potential in one form or another, though most of them did notinclude small-scale projects by the definition above. The range of such estimatesreflects uncertainty about the premise on which they should be based. Francis, of the Department of Energy, 1 has suggested that there are three broad categories inwhich estimates may be placed, namely:

(a) Gross river potential is approximately the summation of annual runoff times potential head.


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additional gauges which could prove useful, and in every case an approach to theWater Authority is worthwhile to obtain flow data and to establish if there areany requirements for compensation flow.

For run-of-river hydro-electric projects, the daily flow duration curve (FDC)provides the required data. The FDC shows the percentage of time that certainvalues of discharges are equalled or exceeded. Duration curves for long periodsof runoff (in excess of 5 years) are utilized in deciding what proportion of flowshould be used for generation, since the area under the curve represents volumeand hence directly affects energy output. Figure 1.1 shows FDCs for the RiverItchen at Allbrook, near Winchester, and the River Ogwen, near Bethesda, NorthWales.

The shape of the curve is also of importance: a generally flat curve representsa river with few flood flows, probably extensively supplied from groundwater; asteep curve indicates a flashy river with frequent flood flows and comparativelylow flows during dry weather. Such characteristics indicate the system of flowadjustment that is required to utilise the flows available. In cases such as theRiver Itchen where flows are relatively steady, a daily adjustment of flow may beall that is necessary. However, for flashy rivers such as the Ogwen, continualflow adjustment may be necessary to utilise all that is available.

In general, where there are no constraints on the scale of development, the 30%exceedance flow from the FDC may be adopted as a first estimate of thedesigned capacity for the scheme. Following the evaluation of costs, energyoutputs and value of energy production for several capacities, both above andbelow that corresponding to the 30% exceedance flow, the design parametersmay be modified to optimise the size of installation. For run-of-river sites, theFDC is fundamental to the calculation of energy output.

Where long-term flow records at a particular site are not available, it isnecessary to estimate the FDC from other readily available data, using anempirical method. Such methods of flow estimation depend on physical andclimatic conditions affecting the catchment. Rainfall data are often utilised, asthey are generally widely available and cover longer periods than river

discharges.One such method is through the use of unitised FDCs. 6 FDCs from establishedgauging points are unitised by dividing through the relevant catchment area andannual rainfall so that they represent flow from 1km 2 of catchment with anannual rainfall of 1 metre. Such unitised curves can be used to represent the generalflow conditions of a particular region. When applied to a specific catchment withinthat region, the unitised curve is factored by the appropriate catchment area andweighted annual rainfall. This method has the advantage that FDCs are producedfrom which energy can be directly calculated. The accuracy of the FDC produced

is dependent on the similarity of the particular catchment to the gaugedcatchment, since even within the same region significant hydrologicaldifferences can exist.

POTENTIAL FOR SMALL-SCALE HYDRO-POWER 3


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1.3Scotland

The first published estimate of hydro-power potential was that of the WaterResources Committee in 1921. 7 The potential was estimated at 1700GWh perannum. This is the lowest of the Scottish estimates, probably because of therudimentary nature of Scottish electrification in 1921 and, perhaps, the strong

lobbying of non-resident Scottish landowners.In 1942, the Cooper Committee suggested a potential of 4000GWh per

annum, and shortly afterwards the Hydro-Electric Development (Scotland) Act1943 was passed setting up the North of Scotland Hydro-Electric Board(NSHEB). When NSHEB published its development scheme in 1944, it foresaw102 projects producing 6270GWh per annum. This figure was revised again byWilliamson, 9 who suggested that the annual output could exceed 8000GWh.

In 1962, the Mackenzie Committee reported a technically viable potential of 7250GWh per annum, and in 1981, with a resurgence of interest in hydro

developmentafter a 20 year lullNSHEB re-estimated the Scottish potentialand concluded in a paper to the Economic and Social Research Council that thetechnical potential was 8500GWh per annum (2700MW installed) and that the

Figure 1.1 Flow duration curves: river with few flood flows (left); flashy river (right).

4 SMALL-SCALE HYDRO-POWER


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economic exploitable potential was 5100GWh (1630MW installed). Since thislast study considered the lower power limit to be 50kW, it is clear that there is alarge number of quite small sites in Scotland that have not yet been assessed.This is hardly surprising, since small schemes do not justify the transmissionlines and access roads which are necessary in many parts of the country.

From such evidence as exists already, it is probable that small-scale schemesin Category (b) with a total potential output of at least 180MW are technicallyexploitable, though the proportion of these which would also merit a Category(c) classification, as being economically viable, could only be an informed guessperhaps a third, or 60 MW, producing, say, 260GWh per year.

Table 1.1 Total potential hydro-electric power in the United Kingdom

Existing hydro-

electricinstallations

Further major

developmentsproposed but notbuilt

Estimated small-scale (5kW5MW)

sites

Technicallyexploitable*

Economicallyexploitable*

MW GWh/y MW GWh/y MW GWh/y MW GWh/y

Scotland

1270 4000 350 1100 180 790 60 260

Wales 120 246 230 8 390 70 300 25 110

England

9 20 32 160 14 75

NorthernIreland

Negl. 1 40 110 35 150 18 75

Total 1399 4267 620 1600 317 1400 117 520 Notes* Power capacity estimated at 30% exceedance, which on most British rivers gives a 50%

plant factor or thereabouts,includes Kielder scheme (under construction).These values reflect the high utilisation factors of water supply schemes, which are

typically >60%.

1.4Wales

In Wales, as in England, public electricity supply is the responsibility of theCentral Electricity Generating Board. The present installed capacity of CEGBhydro-power stations in Wales is 114MW, producing annually about 215GWh.

In addition, there are Water Authority schemes totalling about 5.7MW,producing 41GWh per annum. The load factors represented by these figures, 0.22 and 0.82 respectively, demonstrate only that the CEGB values peaking



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capacity highly, whereas Water Authorities are using near-constant discharges toproduce and sell energy to their Electricity Boards.

The hydrometric areas covering Wales have recently been examined for theirsmall-scale potential for the Department of Energy by Salford University. 3 Some565 sites were identified: they would have a combined capacity of about 70 MWand an annual energy output of 300GWh. The arbitrary lower power limit in thisstudy was set at 25kW and the estimate of scheme capacities ranged from thatfigure to 3200kW, It is estimated that up to 50% of these sites might come withinCategory (c) .

1.5England

The first published data about the hydro-electric resources of England were againthose of the 1921 Water Resources Committee, which suggested an energyproduction of 180 GWh per annum. The Committee made it clear that this wasby no means the total potential, which they were unable to estimate.

A recent study 4 of the English water industry commissioned by the Departmentof Energy, and again limited to powers of 25kW or above, has revealed 66 siteswith power potential of 8.4 MW and potential energy of 48 GWh per annum.The economically exploitable proportion of these is indeterminate, but it may beabout two-thirds. There are, in addition, certainly some hundreds of sitesunconnected with the water industry that could be developed, and many otherswould generate powers of less than 25kW, the total of which has not been estimatedsince data are widely dispersed and have not been systematically examined. Toprovide a first indication, it would be reasonable to quadruple the water industrypotential and to assume that one-third of these extra sites would be economic.These assumptions lead to Category (b) and (c) figures of 32MW, 160GWh and14MW, 75GWh respectively.

1.6

Northern Ireland

There has been no recent study of small hydro potential in Northern Ireland.More than 200 existing weirs are technically exploitable, but there are fewexamples where electricity is being generated. There are several excellent siteson the Six Mile Water and Blackwater Rivers which would almost certainly beeconomic also.

The western part of Ulster was not fully developed for water power during theindustrial revolution; nor were the upland sites on the Antrim plateau. It is

estimated that there may be up to 100 new sites for small-scale installations.Based on topography, rainfall and comparison with similar areas moreintensively studied, it would be reasonable to assume a technical potential of



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about 150GWh per annum. This is equivalent to about 3% of current NorthernIreland electrical generation. A Category (c) figure might be about half of this.

Two larger schemes on the Lower Bann and the River Mourne have been wellresearched and would certainly now be economic. They would have a totalinstalled capacity of 40MW and would generate 110GWh per annum.

1.7Summary

The information given in this paper is summarised in Table 1.1 .The estimates in this paper are based on the sources cited, on the references

and on private communications from A.T. Chenhall and F.G.Johnson of theNorth of Scotland Hydro-Electric Board and Dr S.R.Cochrane of QueensUniversity, Belfast, which dealt, respectively, with Scotland and NorthernIreland.

It is now reasonable to assume that there are upward of 500 sites in the U.K.where small-scale hydro-power could be developed with a better-than-evenchance of economic viability.

References

1. Francis, E.E. Small-scale hydro-electric development in England and Wales. InConference on Future Energy Concepts, Institution of Electrical Engineers,London, Jan 1981.

2. Electricity in Scotland: Report of the Committee on Generation and Distribution inScotland. HMSO, Cmnd 1859, London, November 1962 (the Mackenzie Report).

3. Department of Energy. Report on small-scale hydro-electric potential of Wales.University of Salford, Department of Civil Engineering, Oct 1980.

4. Department of Energy. Report on the potential for small-scale hydro-electricgeneration in the Water Industry in England. University of Salford, Department of Civil Engineering, April 1984.

5. Department of Environment. Surface Water: United Kingdom, 197680. HMSO,

London, 1981.6. Wilson, E.M. Engineering Hydrology, 3rd Edition, p. 117. Macmillan, 1983.7. Report of the Water Resources Committee. HMSO, London, 1921.8. Hydro-electric works in North Wales. Further developments. Report to North

Wales Power Company, September 1944. Freeman, Fox & Partners and JamesWilliamson, 25 Victoria Street, London SW1. Internal Report No. 54.

9. Williamson, J. Water power development in Great Britain. I.C.E. Joint Summer Meeting, Dublin, 1949.



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Section 2Hydro-electric plant and equipment

J.Taylor

and

C.P.Strongman

Merz and McLellan

Newcastle upon Tyne

Hydro-electric plant and equipment

2.1Introduction

The Watt Committee working group on small-scale hydro-power was set up toexamine the potential for development of further low-head hydro-electric poweras a useful and economical addition to the energy resources of the UnitedKingdom and to make suggestions for further study and action. When theworking group discussed its terms of reference, consideration was given toextending its examination to overseas potential. A decision was made, however,to limit the study to development in the U.K., but with the thought that it wouldbe welcome if, in doing so, the working group could encourage developments byU.K. plant and equipment manufacturers for which there might be salesopportunities overseas. Subsequently, the scope of the examination was changedfrom low-head to small-scale hydro-power, thus covering the entire headrange of installations of small capacity. This Section of this Report is confined tothe mechanical and electrical plant and equipment, although it excludes penstocksand gates (normally considered as part of the civil works) and the civilengineering aspects, statutory and legal matters, potential in the U.K.,environmental considerations and so on, which are dealt with in other Sections.

2.2Definitions

There are many definitions of small-scale hydro-power, and it is not possible tobe precise about them because the concept is somewhat subjective. The electricalengineer thinks of a definition in terms of the output of the generating set,


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whereas the hydraulic engineer places more emphasis on head and flow, which

define the selection and size of the plant and whose product gives output. Thecivil engineer, although inextricably bound by the head and flow, is alsoconcerned with the physical dimensions of the plant and equipment insofar asthey affect the design of the civil works. For the present purpose, it is proposedto consider a definition in terms of electrical output. Output of the generating setin the range 010MW, and even higher, has been quoted in several papers andpublications; consequently there is a tendency to avoid defining what small-scalehydro really meansperhaps the International Electrotechnical Commission(IEC) should give some attention to this. The present working group decided to

confine itself to an upper limit of 5 MW, largely because of the anticipatedpotential for future small-scale hydro-power in the U.K. Within this range otherdefinitions are referred to, as indicated in Table 2.1 , but there can be no hard andfast rule.

Table 2.1 Definitions of hydro-electric schemes

Small hydro 25MWMini-hydro 500kW-2MWMicro-hydro 500kW

Figure 2.1 Vertical Francis turbine.

HYDRO-ELECTRIC PLANT AND EQUIPMENT 9


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A further category was suggested by one source, namely pico-hydro, coveringsets of 15 kW; but in fact there is no real logic in using picoor indeedmicrounless these terms are related mathematically to the size of the plant.

Although generating set sizes in the 15 kW range are not likely to be of interest to utilities for possible connection to the Grid, * such hydro-electricdevelopment should be encouraged. Many potential and existing privatedevelopers, such as members of the National Association of Water Power Users(NAWPU), find this to be a very useful range for domestic, farm and small localcottage industry applications in rural areas of the U.K.

This paper is confined to small-scale hydro-power installations designed forthe generation of electricity. It is acknowledged, of course, that directmechanical energy can be provided more cheaply than electrical energy. Theconcept of harnessing water for mechanical energy goes back for centuries,during which the water-wheel was used to produce small amounts of power forgrinding corn and later was developed for direct-drive industrial uses: thereremains a large number of old water-mills in the U.K. which could be developed.Indeed, many of them have been developed already, as publicised by NAWPU,and are used for stone-grinding, processing grain for animal feedstuffs, corn-milling, paper manufacture, flour-milling, snuff-grinding, the manufacture of cloth and textile products, wood working, forestry work, farm machinery etc.

2.3

GeneralThe technology of hydro-electric power is well established in the U.K., andincludes plant that is in service, the design and manufacture of plant andconsulting engineering services. The scope of the technology extends from smallto large generating sets and includes their associated valves and ancillary plant.Manufacturers of plant such as water turbines, pump-turbines, waterwheelgenerators and generator-motors have supplied their equipment for power stationsin the U.K. and abroad. Whereas many of the schemes were landmarks in hydro-

power development on account of size or design innovation, others were for run-of-the-mill schemes. There are numerous examples of plant that is now regardedas being in the category of small-scale hydro.

Consulting engineering services for hydro-electric power have also beenprovided in the U.K. for many years. Again, a full range of types and sizes of scheme has been covered; notable major schemes have been engineered as wellas small ones, the extent of the service and the design and engineering resourcesbeing adapted as required. Many of the small schemes in fact constitute the

* The legal and financial conditions for connection of private electricity generatingcapacity to the national public electricity supply network (the National Grid) aresummarized in Sections 4 and 5 of this Report.



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initial power developments in the country or region. The associated plant andequipment can originate from companies abroad as well as from British firms;consequently, experience in the application of suitable plant is both shared andextensive.

Examples of small-scale hydro-power installations in the range presentlyconsidered are numerous in Scotland, operated mainly by the North of ScotlandHydro-Electric Board (NSHEB) but also privately (for example, the aluminiumworks at Lochaber and Kinlochleven). There are also a few small schemes inEngland and Wales, but few in Northern Ireland. Most of the possible types andarrangements of generating plant are already well represented in the U.K.installations. Although some plants have been in service since the turn of thecentury, the 1920s saw an increase in activity; then, with the formation of theNSHEB in 1943, many small schemes were planned and installed until about theearly 1960s. Currently the NSHEB is proceeding with a number of small run-of-river developments.

With regard to design and manufacture, most large generating-plantmanufacturers in the U.K. also cater for the small-scale hydro-power market, and

Figure 2.2 Horizontal Francis turbine.



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there are smaller companies that specialise exclusively in this field. In view of the limited U.K. potential for the development of hydro-power, much of thisplant has been manufactured for installation abroad.

The selection of generating sets and plant for small-scale hydro-powerapplications is firmly based. Likewise, the selection of water turbines to suit thehydraulic conditions and of generators compatible with the loads or systems towhich they are connected is made generally in accordance with establishedprocedures. Nevertheless, there is scope for simplification and standardisation.This also applies to the ancillary plant.

2.4Water Turbines

All the available conventional types of water turbine are suitable for small hydro-power applications. The most common turbines for low- to medium-headapplications are the Francis and the Kaplan or propeller type. Apart from thevertical-shaft arrangement, the latter may be arranged as a bulb turbine, in whichthe turbine and generator are accommodated in an enclosure within the waterpassageway itself, as a tubular turbine, where the generator is located outside thewater passageway, or as a straight-flow turbine (Straflo), in which the generatorrotor is mounted on the periphery of the turbine runner. In addition, the cross-flow turbine, which is a partial admission (impulse/reaction) type, can be usedfor low- to medium-head applications. For high-head applications, Pelton andTurgo impulse turbines, which can be supplied for very small outputs, areemployed.

Figure 2.3 Kaplan turbine.



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In the selection of the type of turbine there are overlaps between the differentdesigns that can be adopted for a given head; therefore other factors, such asspeed, submergence and efficiency, have to be compared.

Other possibilities are centrifugal pumps in reverse rotation and marine bow-thrusters (ships propellers). Further possibilities, such as river-current turbinesand commercial lift hydro-engines, are at the experimental stage, and have beendisregarded in the present study.

2.4.1Francis turbine

The Francis turbine (Figures 2.1 and 2.2 ) is of the reaction type, in which therunner receives water under pressure in an inward radial direction and dischargessubstantially in an axial direction. The main components of the Francis turbineare the fixed-vane runner, spiral casing, adjustable guide vanes and draft tube.The Francis turbine is suitable for a head range of about 10300 m and ratings of 100kW. The shaft arrangement can be vertical or horizontal.

2.4.2Kaplan/propeller turbine

The Kaplan turbine ( Figure 2.3 ) is an axial-flow reaction turbine and is basicallya propeller type with adjustable blades. The water enters the spiral casing andafter passing the runner blades flows through a draft tube to the tailrace. Thistype of turbine has a high efficiency over a wide range of heads and output andhas a high specific speed. Governing is achieved by means of adjustable guidevanes and runner blades.

The propeller turbine is similar to the Kaplan but does not have adjustableblades.

2.4.2.1

Bulb turbine

With the bulb-turbine arrangement ( Figure 2.4 ) the generating set is contained ina capsule accommodated in the water passageway. It is a very compact and self-contained unit. There can, however, be problems with cooling the generator andaccess to the generator itself, although for small units the generator can beremoved in its entirety for maintenance. For reasons of economy the generatormust be of small diameter and therefore low inertia, thus limiting the applicationof bulb sets to connection with electrical systems of adequate size to maintain

electrical stability. The bulb turbine is suitable for a head range of about 520 mand ratings of 300kW.



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2.4.2.2Tubular turbines

With the tubular turbine ( Figure 2.5 ), the generator is located outside the waterpassageway with a long shaft drive and a simple seal arrangement; the generatoris therefore easily accessible for maintenance. A gearbox can be accommodatedbetween the generator and turbine if required to enable a high-speedand thus

cheaper generator to be employed. It is suitable for heads up to about 15m andratings of 50kW and upwards.

2.4.2.3Straight-flow turbine

The Straflo turbine ( Figure 2.6 ) is a development of an earlier design in whichthe generator is located on the periphery of the runner; there is thereforeadequate space for a large generator with large rotational inertia. The

arrangement is compact, and there is no drive shaft. Consequently, the size of thewater passageways, and hence the extent of the civil works, can be considerablyreduced. This type of turbine is suitable for a head range of about 230 m andratings of 500kW.

2.4.3Cross-flow turbine

The cross-flow turbine ( Figure 2.7 ) is a radial/impulse type of low-speed turbine.

Its dimensions at low head and high flow are greater than those of comparableconventional turbines. It has simple blade geometry and lower construction coststhan the conventional turbine. For low heads, the blades can be manufactured

Figure 2.4 Bulb turbine.



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from cheap materials because the bending forces are low. Efficiency is modestbut the curve is flat over a wide flow range. Gear boxes can be employed toincrease speed to suit economical generator designs; however, they reduce theefficiency.

This type of turbine is suitable for a head range of about 2200m and ratingsup to about 1MW. Accordingly, it is quite suitable for the lower end of the micro-hydro range, because of its versatility and relatively low cost.

2.4.4Pelton turbine

The Pelton turbine ( Figure 2.8 ) has an impulse wheel on which are mounted cup-shaped buckets that have a radial partition or splitter in the centre to divide theimpinging water-jet which issues from a nozzle on the end of the penstock. Thewheel is encased to prevent splashing. The governing mechanism is an adjustablespear or needle and a jet deflector. This type of turbine is suitable for high heads within the range 201000mand ratings from 10kW upwards. For lowoutputs one or two jets would be employed and a horizontal shaft arrangementwould be appropriate.

Figure 2.5 Tubular turbine.



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2.4.5Turgo turbine

The Turgo turbine is an impulse turbine actuated by a water jet in which the

water enters on one side of the runner and discharges at the other. It is suitable forheads of up to about 300m. The Hydec unit, manufactured by Gilbert Gilkes andGordon Ltd. (see Table 2.4 ) is a turbine and generator package incorporating aTurgo water turbine.

2.4.6Pumps running in reverse

Conventional water turbines, as described here, with the exception of the

domestic types, are expensive compared with centrifugal pumps run as turbines.Consequently pumps running in reverse as turbines are commonly employed onmicro-hydro installations in developing countries. This has prompted pumpmanufacturers to investigate the turbine characteristics of their pumps.

Since a centrifugal pump lacks guide vanes, other means have to be used forstarting, stopping and loading the set, for instance by adjustment of inlet-valveopening. Developments in this regard are taking place, and for sets usinginduction generators connected to the grid pumps run in reverse appear to besatisfactory. The lower runaway speed compared with a Francis turbine should

give cost advantages.

Figure 2.6 Straight-flow turbine.



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2.5.1Synchronous generators

Synchronous generators are normally employed for generating sets connectedeither to an isolated system or a grid system. If they are connected to a grid,

synchronising equipment is required.

2.5.2Induction generators

An important factor in the employment of asynchronous or induction generators,which are basically induction motors driven above synchronous speed, is thesystem to which the generator will be connected and the capability of that systemto supply the necessary magnetizing power. The fact that the induction generator

derives its excitation from the system and cannot therefore run completelyisolated (capacitor bank excitation excepted) is a disadvantage where a suitablesystem is not available. It also suffers from the disadvantage that the naturalinertia of the generator is considerably less than that of the equivalent, speciallydesigned, synchronous generator. This can, however, be compensated for byadding a flywheel. These disadvantages are to some extent offset by thefollowing important advantages.

A separate excitation system is not necessary: this relieves the unit of sliprings,brushes, field circuit breaker, discharge resistor and automatic voltage regulator.

Expensive synchronizing equipment is also not needed; the generator circuit-breaker is simply closed at or near synchronous speed and the machine pullsitself into step. As a consequence, the machine is generally without stabilityproblems. Because of these factors the generator may require less maintenancethan the equivalent synchronous generator; it is also cheaper. Its efficiency issomewhat lower than that of a synchronous generator, but this is relativelyunimportant when considering hitherto uneconomic installations. There are speedand output limitations but they would probably not apply within the output rangeof small hydro.

Although, generally, experience on induction generators of large size islimited, a number have been installed by the NSHEB in the range 50kW5MW.

2.5.3Standard induction motors

The use of standard squirrel-cage induction motors, instead of the wound-rotortype, as generators is a possibility and, provided that care is taken to avoidoverspeeding, this is a cheap solution for small-scale hydro-power. Overspeeding

can be avoided by the use of overspeed release clutches.



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For unattended machines thet supply a local load the selfregulating generatorisan obvious choise. In principle, it derives its excitation from the armature voltageand current of the generator via a compounding circuit. An important benifit of this arrangement is that excitation is sustained when the generator is subjected toashort circuit. It is usual for a compound sysyem to include an automatic voltageregulator in order to achieve closer voltage control and assist rapid voltagecorrection following sudden load chnages. In the case of mini- and micro-installations, the excitation and regulation equipment can with advantage form agenerator-mounted package. A brushless generator may also be preferred so thatmaintenance requirements are minimised ( Figure 2.9 ).

Larger machines, especially those connected to the grid, need an excitationcontrol system matched to the requirements of the generator and supply system.

2.7Governing

The principles that apply to the governing of large hydro-electric generating setsare relevant to small sets. The objective is to maintain constant speed orfrequency by controlling the turbine flow to match changes of load; it is assumedhere that the plant is needed to supply an isolated system or local load, or to playa major part in the frequency control of a small system. Associated factors arethe time taken to achieve the desired flow and the flywheel effect of the set.Governing requirements therefore have an influence on plant costs. In addition totheir basic function, governors also facilitate starting, stopping, synchronising,parallel operation of generating sets and load sharing between them, and providesecurity against prolonged overspeeding.

Should the small generating sets feed into a large system, governing may notbe considered necessary, particularly in the case of induction generating sets.Then the governor actuator could be dispensed with, leaving the remainingmechanism to serve as an output or load controller. However, means for starting,running-up and shut-down of the set must still be provided.

The main elements of governing systems ( Figure 2.10 ), which apply equally tolarge and small hydro sets, and alternative possibilities are itemised below.

2.7.1.Governor system

2.7.1.1

Actuator

The actuator is a stable device or mechanism located on the governor head whichsenses a speed change and converts it into the displacement of a collar or othercomponent serving as a signal to an amplification system. The actuator can be



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2.7.1.3Pressure oil

For spring-opposed servomotors, a storage receiver for the oil supply is notalways necessary. For double-acting servomotors, providing large forces over a

short operating time, pressure-oil receivers are needed ( Figure 2.11 ). In bothinstances, a pumping set provides the pressure-oil supply.

2.7.2Alternative possibilities

2.7.2.1Output controller

The application of a microcomputer to the output control of a hydro-electricgenerating set is an economical alternative to the conventional mechanical orelectronic governor; this has been done by the NSHEB at Sloy power station. Inaddition to providing continuous control of the frequency and power output of the generating set, the controller can cater for sequential control of the run-upand shut-down operations and the monitoring of the plant. The output controlleracts on the conventional servomotor equipment of the governing system.

It is perhaps too early to say whether or not the microcomputer governor willmatch the reliability of the conventional mechanical or electronic governors. Onthe other hand, improved speeds of response can be achieved without loss of stability.

2.7.2.2 Load controller

A wholly electrical system for speed governing that has recently been introducedfor micro installations may possibly be extended to the low-power end of the

mini-installation range ( Figure 2.12 ). It is applicable to installations that operateindependently of a public supply network or other parallel connected generators.Speed is regulated by maintaining constant active load on the generator. The

flow through the turbine is constant at constant head at the full load value, andthe available hydraulic energy is converted to electrical energy at all times,leaving no imbalance to cause significant speed changes. Any positive differencebetween generator output and supply-system load demand is absorbed in adumping or ballast resistor. The only back-up that may be necessary is an inletvalve to isolate the turbine in the event of failure of the speed/load regulator or

of a bypass valve.The ballast resistor and its regulator can take various forms. For example,discrete resistor sections can be selected by electromagnetic or solid-stateswitching; alternatively, a phase-controlled triac, or anti-parallel thyristor pair



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with a single ballast resistor, may be employed. The regulator unit comparesspeed, and load, against fixed references to provide switching signals.

Power dissipated in the ballast resistor need not be wasted. For example, watercan be heated for use in a space-heating system or for a hot water supply. Even if the surplus energy has to be wasted, there will be no cost penalty, since for suchan installation it has to be accepted that there must be a constant flow, whichwhen not needed for energy would run to waste.

Where water economy has to be practised, some form of secondary governingor water-flow regulator may be necessary if the normal demand is considerablyless than the rated output of the machine. If sudden load increases of anysignificance cannot occur, or are not allowed to, such regulation can be quitesimple.

2.7.2.3 Hydraulic brake

The hydraulic brake incorporates a fly-wheel brake, on to which the water isdiverted in the event of load rejection. The tendency to overspeed is therebyopposed and the rate of flow can remain constant. The system is applicable toimpulse turbines.

2.7.2.4

Eddy-current brakeAn older form of electrical governing is the eddy-current brake, in which theload is adjusted to suit the output of the set. The power absorbed by the braking

Figure 2.12 Constant load controller.



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device plus the system load equals the power output of the turbine. The brakingdevice consists basically of a series/shunt-wound magnetic frame, similar to ad.c. motor, in which the main shaft revolves. On the end of the shaft a ferrousdrum is mounted which rotates in the magnetic field set up by the frame. Theshunt winding is connected to the generator terminals, and the eddy currents thatare set up in the drum as it rotates absorb power and cause a braking effect. Asthe load on the generator varies, so does the current in the series winding of thebraking device, partially neutralizing the shunt field. Accordingly, the power of the turbine is shared by the system load and the braking device.

2.7.2.5Variable-speed operation

An alternative method of electrical governing for small-scale hydro, now madepossible by the development of large power static-variable frequency converters,is to allow the turbine to free run. This is a method adopted for wind-drivengenerators and considered for some wave-energy systems. The generatorsoperate at variable frequencies according to the load, and the output is convertedto direct current controlled at a constant value by a current regulator, and back again to alternating current ( Figure 2.13 ). In effect, the power is transmitted tothe a.c. system via a back-to-back d.c. link. The disadvantages are the need tovary a number of units to suit the constant flow as the load varies, the lowefficiency at part load and the need to design for fairly frequent runawayconditions.

2.8Electrical System Design

In order to limit total costs and thus assist in the justification of small hydroprojects, economies have to be made, not only in the selection of turbine,generator, governing and excitation, but also in the electrical system itself.

Although a unitised system, comprising a generating set connected directly to itsown step-up transformer, is common for most large installations, it is sensibleand rational with small hydro-electric installations, if there is more than one set,to connect them through circuit breakers to a common busbar at generatorvoltage with a single step-up transformer to the transmission system. Not only isthis cheaper than the unitised scheme, but it provides good operationalflexibility. It should be mentioned that reactive power sharing is more easilyaccomplished with the unitised arrangement, however. When bussing at generatorvoltage, care must be taken not to exceed the fault-carrying and breaking

capacity of the switchgear and connections; the method of generator earthing andprotection must also be carefully studied. Off-site supplies for station auxiliariescan, however, be provided relatively cheaply.



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2.9Protection

When small generating sets are connected to an Electricity Boards network,obligatory electrical protection is necessary to safeguard the network (Figure 2.14 ). This obligatory protection is set out in EngineeringRecommendation G47/1 issued by the Electricity Council. In addition someguidance is given in Engineering Recommendation G26. *

Figure 2.13 Variable-frequency generator method of load control.



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Figure 2.14 Typical protection diagram for asynchronous generator connected toGrid. Asterisk (*) indicates obligatory protection.



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Figure 2.15 Typical protection diagram for synchronous generator connected toisolated system.



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By contrast, this treatment cannot be given to small installations, as theircapital costs are not sufficiently high to warrant expensive engineeringmanagement. Consulting engineers, specialising in hydro-electric project designand engineering, have therefore adapted to this situation by

Table 2.2 Small hydro-electric installations in Scotland

Station Gross head,m

Plantcapacity, kW

Station Gross head,m

Plantcapacity, kW

Sron Mor 52 15000 Glenmoriston

14 1160

Cuaich 27 12500 Beannachran 10 1160Loch Ericht 55 12200 Loyne

Tunnel26 1550

Mullardoch 28 12400 Stronuich 10 1210Achanalt 20 12400 Pitlochry 14 150Lochay 182 12000 Orrin 42 1200 and

15617 154 Meig Dan 15 176

Lubreoch 30 14000 Tobermory 42 1200 and1 80

Dalchonzie 28 14000 Luichart 18 185Lednock 92 13000 Torr Achilty 14 1100

Ceannacroc 91 14000 Clunie Dam 18 1175Lairg 10 13500 Elvanie 35 1300Cassley 114 11 500 Duchally 26 1325 and

1 125Striven 124 23000 Quoich 38 1350Loch Gair 110 23000 Misqeach 37 1350Lussa 117 21200 Kerry Falls 57 1500Storr Lochs 138 2950 and

1800Gaur 30 1160

Kilmelfort 112 12000 and183

Invergarry 64 1285

Mucomir 7 11750 and1200

10 130

Kerry Falls 57 2500 and1250

Vaich 7 1320

NostieBridge

151 2625 Culligran 60 12000

Loch Dubh

(Ullapool)

167 2600 Gorton 79 1100

Morar 6 2375 Errochty 92 1525



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selection of materials and of runner sizes for specific head ranges, resulting instandard casings, shaft and bearing arrangements etc.

With regard to generators, whenever possible only standard generators shouldbe specified. The employment of standard induction motors run as generatorsshould be considered for grid-connected mini- and micro-installations.

Where small synchronous generators are employed, the self-regulating set or abrushless system may be the best solution for the excitation.

For the mini- and micro-range of sets, manual start-up and stopping withappropriate auto-trip facilities should be adequate. A micro-processor maypossibly be employed, however, to cater for sequential starting and stopping andcontinuous frequency and power output control if the cost is right.

Protection of the installation should be as simple as possible and the minimumnecessary to safeguard the plant. If the sets are grid-connected, cognizance mustbe taken of the Electricity Councils Recommendations.

From studies made, the future development of small-scale hydro in the U.K. islikely to be mainly in the mini- and micro-hydro range of set sizes and thesummary and conclusions ( Section 6 of this Report ) have been biased towardsthis. Whilst Section 2 is confined to small-scale hydro in the U.K., it isrecognized that in developing countries a considerable degree of improvisation inhydro-electric engineering is practised. It is unlikely, however, that suchimprovisation would be tolerated in the U.K. for grid-connected installations.

Finally, what are the costs of the electrical and mechanical equipmentassociated with small-scale hydro?an easy question to ask, but a difficult oneto answer. Much depends on the country in which the equipment is manufacturedand installed. If it is in a developing country, with relatively inexpensive labour,it will be cheaper than in a developed country. Indeed, U.K. manufacturers areknown to arrange for some of their heavy engineering and sub-assembly work tobe done in the Far East because of the high cost of labour in Europe. Figure 2.16indicates the form of cost envelope, showing cost per kilowatt plotted against setoutput across the head range. The curve has been derived from actual installationcosts and budgetary information provided by manufacturers and public utilities

in the U.K. It does not pretend to be definitive, and many installers will say thatthe work could be done much more cheaply. These claims must, however, bemeasured against the institutional barriers that may or may not apply; thestandards of engineering that are set also affect the cost. The cost curveillustrated in Figure 2.16 most certainly does not claim to represent the installerwho buys a small domestic turbine for private use: he is not bound to providesophisticated control and protection requirements, and may not be hampered bytoo much bureaucracy. As to the costs of installations in the U.K. that are connectedto the Grid, the envelope of costs shown in Figure 2.16 is realistic.



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Table 2.3 Small hydro-electric installations in England and Wales

Station Plant capacity, kW

Cwm Dyli 120001100012000

Dolgarrog 1500015000

Mary Tavy 32202650

Morwellham 2320Chagford 131

The schemes listed here are those operated by the CEGB that give output of 5 MW and

below.

Table 2.4 Suppliers of water turbines in the United Kingdom

Supplier Address and telephonenumber

Types of turbines

Boving & Co. Ltd. Villiers House, 4147Strand, London WC2N5LB (01) 839 2401

Francis; Pelton; Kaplan;Propeller; Tubular

Gilbert Gilkes & Gordon

Ltd.

Canal Iron Works, Kendal,

Cumbria LA9 76Z

Francis; Pelton; Turgo

Impulse; HydecWeir Pumps Ltd. Cathcart Works, Glasgow

G44 4EX (041) 637 7141Francis; Pelton; Tubular;Reversed pump; Kaplan

GEC Energy Systems Ltd. Cambridge Road,Whetstone, Leicester LE83LH (0533) 863434

Francis; Pelton; Kaplan;Propeller; Deriaz; Tubular

Armfield Engineering Ltd. Ringwood, HampshireBH24 1 PE (04254) 2405

Francis; Pelton; Cross-flow; Kaplan

Newmills Hydro Ltd. Mill Lane, Island Road,Ballycarry, Co. Antrim,Northern Ireland (09603)78610

Francis; Pelton; Propeller(Kaplan); Turgo Impulse

F.Bamford & Co. Ltd. Ajax Works, Whitehill,Stockport, Cheshire SK41NT (061) 4806507

Propeller (Kaplan);Tubular; Francis; Pelton(micro)

MacKellar Engineering(Grantown-on-Spey) Ltd.

Forest Road, Grantown-on-Spey, Morayshire, Scotland

Micro-hydro propeller;Cross-flow; Pelton

Hayward Tyler PumpCompany

PO Box 2, Luton LU1 3LW(0582) 31144

Reverse pump(submersible generator andother types); Pelton

Evans Engineering &Power Company

Priory Lane, St Thomas,Launceston, CornwallPL15 8DQ

Reaction and impulseturbines up to 100 kW;water turbines (under 1200



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Supplier Address and telephonenumber

Types of turbines

(0566) 3982 kW); U.K. Patent holdersfor electronic load-governing systems

Flygt Pumps Ltd. Colwick, Nottingham NG42AN (0602) 614444

Submersible propeller

Dorothea RestorationEngineers Ltd.

Southern Works, 68Churchill Road,Brislington, Bristol BS43RW(0272) 715337

Reconditioned Francisturbines

Portmore Engineering Ltd. Portmore Road, LowerBallinderry, Lisburn, Co.

Antrim BT28 2JS,Northern Ireland(0847) 651528

Cross-flow

Swift IndustrialDevelopments Ltd.

PO Box 8, Romsey,Hampshire SO5 OGT(0794) 40714

Axial flow impulse withflow control

Water Power Engineering Coaley Mill, Coaley,Dursley, Glos. GL11 5DS(0453) 89376

Cross-flow; Reaction;Second-hand andoverhauled turbines

Westward Mouldings Ltd. Greenhill Works, Deleware

Road, Gunnislake,Cornwall

Water-wheels

Disclaimer. The particulars given in Table 2.4 are given in good faith, but the WattCommittee on Energy takes no responsibility for their accuracy or for anyomissions or for the fitness of the equipment listed either generally or in anyspecific scheme. Developers should discuss their requirements with thesuppliers and seek appropriate advice.

In Tables 2.2 and 2.3 , small hydro-electric installations (5MW and below)operated by the NSHEB and CEGB respectively are listed. In addition to these, a

large number of private hydro-electric installations in the U.K. operate at headsfrom about 0.5m to 220m and outputs between 1.5 kW and 200kW: amongthem, most of the recognised turbine types are employed. Only two or three of these are connected to the electricity boards systems. The remainder are usedfor private purposes only, and some have direct drive applications. NAWPU cansupply reasonably complete lists of them.

Details of suppliers of water turbines in the U.K. are given in Table 2.4 .The authors are indebted to the Partners of Merz and McLellan and to their

colleagues in the firm, as well as to the other members of the working group, for

their valuable help in the preparation of this paper.



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Bibliography

1. Water Turbines for H-E Power. Gilbert Gilkes and Gordon, Kendal, 1974.2. Small Hydro-Power Fluid Machinery. Winter meeting of American Society of

Mechanical Engineers. Chicago, Illinois, USA, 1980.

3. The Power Guide. Intermediate Technology Publication, 1979.4. Gaal, V. et al. Small hydro-electric power stationsa contribution to the solution of the energy problem. Brown-Boveri Review. July/August, 1983.

5. Gordon, J.L. Small hydro puts new challenge to consultants. Energy International,August, 1980.

6. Wilson, E.M. Small scale hydro-power developments in the U.K. World EnergyConference, New Delhi, 1983.

7. Micro Hydro Developments. Hydro Power, December, 1980/January 1981.8. Energy Department gives qualified Yes to small hydro. Electrical Review, April,

1979.

9. Teichmann, H.T. International standardization of small hydro schemes. Water Power and Dam Construction, May, 1983,

10. Generating profits on a small scale. The Engineer, 11/18 August, 1983.11. Giddens E.P. et al. Small hydro from a submersible pump. Water Power and Dam

Construction, December, 1982.12. Generators for small hydro applications. Hydro Power, December, 1980/January,

1981.13. Pereira, L. Induction generators for small hydro plants. Water Power and Dam

Construction, November, 1981.14. Water Power from Weissenburg-Ossberger-Turbinenfabrik GmbH.

15. Garman, P. Development of a turbine for tapping river current energy. AppropriateTechnology, September, 1981.

16. Submersible generator. Electrical Review, 23 September, 1983.17. Friedlander. Reviving low-head and small hydro. Electrical World, August, 1980.18. Makansi. Equipment options multiply for small-scale hydro. Power, May, 1983.19. Small hydro needs its own experts. Water Power and Dam Construction,

December, 1982.20. Marshall, A.F. et at. Microcomputer control of hydro turbines. Proc. I. Mech. E. ,

April, 1983.21. Nair, R. Development potential for low-head hydro. Water Power and Dam

Construction, December, 1982.



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Section 3Civil engineering aspects

N.A.Armstrong

North of Scotland Hydro-Electric Board,

Edinburgh

Civil engineering aspects

In most cases, the end-product of a hydro-electric scheme is electricityproduced by the generator and driven by the turbine prime mover. Although thegenerating plant is vitally important, it is nevertheless usual that the major part of the capital cost of a hydro-electric scheme is absorbed by its civil engineeringaspects. This Section brings to the attention of the developer of a potential small

hydro-electric scheme the salient questons of civil engineering to which heshould be giving consideration when assessing the feasibility of the scheme.

3.1Aqueducts

There is a large variety of types of hydro-electric schemes. The upper end of atypical scheme ( Figure 3.1 ) is dealt with first here, and other aspects are dealtwith progressively, working downstream to the tailrace, the civil aspects of most

of the types that are normally encountered being briefly described.The beginning of a conventional hydro-electric scheme is at a point wherewater collects, usually a loch or lake, a headpond or a river, providing a head of water. This is what the developer has noticed to make him interested in itspotential for power development. This collection point is fed by run-off fromrainfall or snow, falling over its upstream catchment area and draining naturallyuntil it reaches this point. It is often possible, and if so generally worthwhile, toincrease the amount of natural water that is available by tapping adjacentcatchment areas that would not naturally drain into the selected point. This is

usually done by constructing some form of aqueduct system.A first basic point for the developer, therefore, is that the aqueduct system willalmost certainly require planning permission.


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Next, if it is relatively small and does not create a safety hazard for people orlivestock, the aqueduct can be left open; otherwise, it requires to be eithercovered or fenced ( Figure 3.2 ). A buried aqueduct eliminates these hazards, andoverall is generally less expensive.

An open aqueducts gradients should permit the water to flow at a reasonablespeed to achieve a self-cleaning capability if grit, debris or stones can gainaccess; if the rate of flow is slow, the aqueduct is liable to become blocked and tooverflow, particularly on curves or bends. The presence of large boulders whichcould readily block the aqueduct if they enter the system should be checked withcare.

Consideration should be given to making the aqueduct as impermeable aspossible by lining it with suitable material, such as slate, flagstones, granite slabs,bitumen, concrete or steel plate etc.

Problems may arise if the aqueduct is open and liable to spill; this mightseriously affect its banking, which could then be breached and far progressively.Provision should therefore be made to allow the aqueduct to spill automatically atpredetermined points so that excessive water is ejected safely. Alternatively, if possible, the amount of water allowed into the aqueduct system may be limited;for example, the aqueduct may be fed from a river through a pipe which limitsthe entry of water. A rough guide to the size of the aqueduct, if it feeds a storagereservoir, is that it should be capable of handling five times the average flow of water.

It may be necessary to bridge the system where it is crossed by rights of way.

Figure 3.1 Main features of typical scheme.



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of State for Scotland and Wales, and on completion a certificate is issued. A listof the appointed engineers can be obtained from the Institution of CivilEngineers 1 or the Department of the Environment. 3 The dam must then beinspected not less than once every 10 years, again by an engineer selected fromthe panel of appointed engineers.

A new feature of the 1 975 Reservoirs Act is that every dam that is subject tothe Act is required to have, in addition to the 10-yearly inspecting engineer, asupervising engineer selected from a further panel of appointed engineers; 1,3 heis appointed to keep a watchful eye on the dam and to ensure that anyrecommendations made at the inspections are carried out. He reports to anenforcing authority. In Scotland this is the local regional or islands council, andin England and Wales it is the Greater London Council or appropriate countycouncil.

From 1 April 1 986 it will be necessary for all undertakers of large raisedreservoirs to appoint a supervising engineer and to be responsible for payment of his fees in respect of each dam that he supervises. It is probable, in the case of asupervising engineers duties, that the payment, including travel and otherexpenses, for a dam inspection at the present time can be expected to be in theregion of 1000 to 1500.

3.3Dam

Small dams are usually constructed on the gravity or embankment principle(Figure 3.3 ) and are of earth or rockfill. The type of dam selected may depend onits locality: for example, there may be a ready source of suitable material nearby.Alternatively, the type of dam may be determined on environmental grounds if itmust be of a type that blends with the surrounding terrain. The likely severity of floodwater could be another influence on the choice: for example, a concretegravity dam might be considered superior to an embankment dam.

An embankment dam requires a waterproof membrane. If the dam is relatively

small, the membrane could be a simple wall with fill on either side; it would alsorequire an upstream protection face, such as stone or rock, to counteract anyeroding wave action.

Some possible weaknesses of an embankment dam are as follows.(1) There is a danger that the dam may be overtopped with flood water, which

could then affect its vulnerable downstream face.(2) If it is necessary to have an opening through the dam for flushing out

gravel and stones etc., the opening could create a permanent potential source of leakage.

By contrast, the small concrete gravity dam does not suffer these problems: itcan probably be constructed using standard deliveries of ready-mixed concretebut care is needed to ensure that it is well founded on bedrock to prevent itsbeing overturned.



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A serious operational problem could be the build-up of gravel, sand etc.behind the dam, especially in river schemes. The scheme must thereforeincorporate means to flush out this material. Usually this is done by running aculvert through the dam, with a flushing gate. The gate can be on either theupstream or the downstream face of the dam; if the gate is on the upstream face,it may be difficult to clear gravel from the gates tracks, and this might prevent itfrom operating correctly; if on the downstream face, the culvert is always underfull pressure and water will certainly ultimately find any weakness.

The following are practical suggestions if it is proposed that the dam shallscour through a culvert.

(1) The culvert can be continued upstream of the dam to act as a scouringchannel.

(2) The optimum gradient is 1:20.(3) The width of the culvert should exceed its height by a ratio of about 5:3. It

is important to ensure that when the gate is opened water does not prevent accessfor the purpose of reclosing the gate.

Figure 3.3 Embankment dam prior to installation of 1-m high top wave-wallgabions.

CIVIL ENGINEERING ASPECTS 41


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(4) When scour is operated, the rate of flow must not be too low; otherwise,gravel may collect under the gate and consequently it will be difficult to close it.

(5) Conversely, if the rate of flow is too high, only local scouring will takeplace around the entrance to the culvert.

(6) Some arrangement should be made to enable the dam to be deliberatelydrained.

Dams must be designed to cope with floodwaterby discharging usually overa spillway, or occasionally by opening gates.

Guidelines for the quantity of floodwater for which the design of the dammust provide are contained in a Floods and Reservoir Safety booklet, 2 publishedin 1978 and obtainable from the Institution of Civil Engineers. Although itsrecommendations are not mandatory, the inspecting engineer would generallyexpect its requirements to be met. The guide requires that the dam be categorisedas follows:

(a) by location, that is, in terms of the risk to life and property downstream;(b) by type, that is, in terms of its ability to withstand overtopping.

The booklet gives guidelines on the period of time in years which, once the damhas been categorised, must be considered for determining the maximum possibleflood that may occur. The longer the period, the more severe the flood that canbe expected. A small dam would possibly be based on a 150-year flood, or on aneven shorter period if the affected community is small and the risk negligible;but a dam may be required to contain a 10000-year flood, or even more, if acommunity with a higher density would be at risk.

The probable maximum flood (pmf) that can be realistically expected at thedam is dependent on the probable maximum precipitation (pmp), rain plus snowif applicable, for a given duration over the relevant catchment or drainage basinunder the worst flood-producing conditions in the catchment area.

Using these data, the booklet provides guidelines on the amount of flood waterthat the dam must safely discharge.

If in any circumstances the dam would prevent water from going down theresidual river section (between the dam and the place where the power station islocated), it may be necessary to discharge compensation waterthat is, tomake good the shortage of water in that section of the river. This could be tomeet fishery requirements or to maintain a summer amenity, for which the riverbed must be kept wet and fresh. About 5% of the average flow is normallyconsidered to be an adequate discharge for these requirements.

3.4

Pipeline

If the water is conveyed to the power station through a pipeline, the cost can berelatively expensive. Nevertheless, a good choice of types of pipes is available. It



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may be necessary to bury the pipeline for reasons of amenity. A small hydro-electric scheme may have the pipeline above ground: that requires theconstruction of supports.

Pipes suitable for small-scale hydro-electric schemes may be of steel (to BS3601), ductile cast iron, glass fibre, reinforced plastic or asbestos cement (to BS

486). Steel pipes are the commonest. The pipes are usually internally protectedby a spun bitumen or epoxy pitch coating. If below about 1m in diameter, theyare difficult to recoat internally, as a painter cannot readily gain access.Corrosion effects can be reduced if the pipeline is always full of water, but steelpipes require periodic attention to contain corrosion. Standard sizes are availableup to 2m in diameterbut there is no limitation on size. The working pressureof the available pipes is virtually unlimited. The pipe joints may be flanged orwelded, or Viking Johnson couplings may be used. Supports are required aboutevery 12m for an above-ground pipeline.

The painting of a steel pipeline requires some care. If a bitumen type of paintis used, the pipes may require to be recoated internally every 58 years. The paintshould last longer if it is applied by means of a spun bitumen process that is,

Figure 3.4 Fibre-glass penstock pressure pipe; diameter, 0.4 m.



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when applied to new piping. A bitumen coating usually suffers abrasion damage,particularly on the base. When repainting, it is often difficult to apply the paint tothe invert owing to leakage and condensation, even when dehumidificationequipment is used.

External paint has a life of around 1215 years; the more sunlight it is exposedto, the shorter its life. Normally, micaceous iron oxide paint is used.

Ductile cast iron pipe is now becoming a very serious competitor: it isavailable in standard sizes up to 1.6 m in diameter. Its working pressure issuitable for a head of around 250m of water at


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was in fact too rigid; once that problem had been cured, it has given excellentservice.

For the occasions when a pipe is filled or emptied, means must beincorporated to allow the ingress or egress of air. This is especially importantduring emptyingeither planned or accidentalto avoid the danger that the pipemay collapse as a result of vacuum effects.

3.5Screens

Screens are generally installed upstream and at the intake of turbines, but are alsoneeded on occasions at the discharge of turbines for fishery requirements. Theyare installed for the two following basic reasons:

(1) To prevent debrisleaves, grass, twigs, heather roots, stones etc.whichmay block the passages of the turbine, especially the jets of Pelton and Turgoturbines and the guide vanes and runners of Francis turbines. This blockage

Figure 3.5 Concrete intake dam, incorporating self-cleaning overshot screen.



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causes reduction in output, and it is time-consuming to dismantle the turbine toclear it.

(2) To prevent access by fish to the turbine (if fish regulations are in force).The area of screening in this case must be large enough for the flow-rate of thewater to be kept down to the region of 0.251 m/sec.

The spacing of the screen is dependent on the size of the debris that can bepermitted to go through the turbine and the size of fish to be encountered.

Screens have to be cleaned. This can be a particularly onerous and time-consuming task, especially in the late Autumn. It may be advantageous to installan oversize area of screening so that the frequency of cleaning is reduced. Forthe operator of a small hydro-electric scheme to have to rake out the screen in themiddle of the night is no fun! Hand-raking is usual on small schemes. Trashrakes are available, but they require manual supervision; at least one firmproduces a relatively inexpensive automatic screen-cleaning device, however.

A particularly troublesome problem is presented by the debris carried inaqueduct systems. Aqueduct intakes can be designed as self-cleaning devices byallowing the water to pass through a slightly upward- or downward-slopingscreen. This traps the debris, which is then pushed up or down the screen by thewater-flow or by gravity. Eventually the debris tips over the end of the screen,and it is then led to an area away from the path of the water ( Figure 3.5 ). An upward-sloping screen can be used where there is an abundance of water, as in a riversupply.

3.6Power Station

To house the generator and associated equipment, the power station can be afairly simple structure, but it must be weather- and vandal-proof ( Figure 3.6 ).The foundations for the machinery are relatively straightforward, although itshould be kept in mind that it is rotating machinery that they support, so theremay be a certain amount of vibration. It may be necessary to install some form of

crane or lifting device within the station.The station should be on a site where it is not liable to be flooded by externalwater. If possible, arrangements should be made for the station to drainautomatically if an internal pipe fractures: this ensures that the generator,bearings, control panels and electrical gear are not submerged, as repairs in thisevent would be lengthy and costly.

The water from the turbine is discharged along a simple channel or tail-race. Itmay be necessary to fit a gate at this point to prevent back-flooding of the stationif the turbine is dismantled for overhaul or repair.

Two final basic points for the developer of a small hydro-electric scheme arethat he should take into consideration the siting of the station for road access, andif he proposes to feed excess electricity into the National Grid a suitable gridconnection point must be relatively close.



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References

1. Reservoirs (Safety Provisions) Act 1930 (includes Reservoir Floods Standard).Reprinted 1960, 70 pp., Institution of Civil Engineers. Thomas Telford Ltd., 17Great George Street, Westminster, London SW1P 3AA.

2. Floods and Reservoir Safety (an engineering guide), 58 pages. Institution of CivilEngineers (address as above), 1978.

3. Department of the Environment, Seymour House, Whiteleaf Road, HemelHempstead, Hertfordshire HP3 9DE.

Figure 3.6 Compensation water-power station, housing 350-kW horizontal Francismachine operating under head of 32 m automatically controlled by headpond levelequipment.



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Section 4Institutional barriers

E.C.Reed

Northwood, Middlesex

D.J.Hinton

Anglian Water Authority, Cambridge

and

A.T.Chenhall

North of Scotland Hydro-Electric Board,

Edinburgh

Institutional Barriers

Besides the undoubted economic and financial obstacles likely to face thedeveloper of a small potential hydro-electric source in the United Kingdom, it is

recognised that there are a number of legal and institutional barriers. Indiscussions with the National Association of Water Power Users (NAWPU), apaper produced by the Association for the Watt Committee working group

(

Appendix 4 ) identified these legal and institutional barriers as factors inhibitingdevelopment.

To some extent, recent legislation, in particular the Energy Act 1983 (whichreceived the Royal Assent in June 1983) has altered the situation to such a degreethat the working group believes that an examination of the new circumstances is

justified.

The amount of legislation that might apply to a hydro-power developer couldbe vast, depending upon the scale and intent of the development. Most of thislegislation, however, is common to anyone constructing a building or running asmall enterprise. Examples would be the need to obtain planning permission(under the Town and Country Planning Acts in England, Wales and Scotland) or

a

Building Warrant. If the scheme is to be run as a small business, legislationsuch as the Health and Safety at Work Act has to be considered. Since thesematters are not specific to hydro-electric developers, and are at least moderatelyfamiliar, they are not considered further in this Report . Nevertheless, it should be

remembered that they remain part of the overall picture and that they add to thegeneral burden of legislative procedures with which any developer must comply.

The remainder of this Section covers only those aspects of legislation thathave particular relevance to small-scale hydro-electric developments, althoughsome of it may also be of relevance to other electricity autoproducers. Since


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separate legislation and institutions obtain in Scotland, Northern Ireland, Englandand Wales, the significant differences applicable to each region are indicated.

4.1

Water

4.1.1England and Wales

The legislation that may face a small-scale hydro-power developer with regard towater could be considered to be formidable. The matters that are covered bylegislation are: abstraction; pollution prevention; land drainage; impounding; andfisheries. Furthermore, there are ten Water Authorities that administer the

application of the legislation in their respective areas in England and Wales.These authorities and various other bodies were consulted by the working group.

(a) AbstractionThe licensing of, and the charges for, the abstraction of water are certainly the

most complex part of the water problem for small-scale water-power users, andit is worth noting that NAWPU was formed, among other things, to ease theconstraints with regard to abstraction caused by the Water Resources Act 1963.Under Section 23(1) of that Act, no-one may abstract water from a source of supply except in pursuance of a licence. The 1963 Act gave powers of

enforcement to the river authorities, and, as a result of differing interpretationsamong these authorities as to the licensability of use for power generation,representations were made to the Parliamentary Commissioner forAdministration particularly in relation to charges arising from the licences. Thisled in 1 974 to the issue of a memorandum by the Department of theEnvironment and the Welsh Office entitled Use of Water for Milling or PowerGeneration: Circumstances in which a Licence is Required, which is included asan appendix to this Report (pages 5355).

The Water Authorities are entitled to levy a charge on the whole of the

licensed abstraction in accordance with charging schemes made under Section 31of the Water Act 1 973. All the Water Authorities, however, drew attention tonew legislation which was introduced in the Energy Conservation Act 1981, andparticularly to Section 16 which revises Section 60(2) of the Water ResourcesAct of 1963. Broadly speaking, the 1 981 Act refers to the need to conservesources of energy and the desirability of preventing water charges frominhibiting the use of water as a source of energy. All Water Authorities wereprepared to give consideration to this by allowing reduced charges in appropriatecircumstances, but the discretionary nature of these powers has led to wide

differences in interpretation, and a degree of uncertainty for the small hydro-powerdeveloper.

(b) Pollution prevention

INSTITUTIONAL BARRIERS 49


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Most small-scale schemes for the discharge of water from a turbine would notbe such as to be considered a trade effluent, and therefo

small scale hydro power

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