Novak P. Developments in hydraulic engineering

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Thus the inherent energy of the water masses stored in a reservoir, i.e. the potential work

that could be gained by completely emptying it without losses, can be expressed as

(20)

where H

is the height pertaining to the centre of gravity of the V storage capacity of the

reservoir. From eqn (5) and by substituting 9810 N/m

for γ, the physical energy potential

of the reservoir can be converted into the usual technical unit:

(21)

Obviously, owing to the various kinds of losses, only part of this physical energy can be

converted into useful work. The varying physical power is given by eqn (16), where Q

depends on the opening of the outlet gates and turbines and H pertains to the water level

in the reservoir at any particular instant. On the other hand, in periods of inflow to the full

reservoir and assuming that the outflow can be kept in balance with the inflow, the power

is permanently related to the head H

Reservoirs can be characterized according to height of the dam,

storage capacity,

created lake surface or inherent physical energy, according to eqn (21).

According to a most up-to-date publication

the world’s highest dams, of 200 m or

more, and the world’s largest reservoirs, equalling or surmounting 50×10

(50 milliard

; according to English usage 50 billion m

; according to SI definition 50 giga-cm

), are

listed in Tables 2 and 3.

3 CLASSIFICATION OF HYDROPOWER UTILIZATION

3.1 Harnessing of Watercourses (Traditional Water Power

Development)

The theoretical (physical) potential of all watercourses of the world evaluated according

to eqns (17) and (18) has been estimated by various authors and institutions during the

last decades.

6,9–11

The assessment of the world’s theoretical hydropower capacity (related

to the annual mean discharges) is around 5·6 million MW, while estimation of the so-

called installable (available) capacity varies between 2·3 million and 3·8 million MW

(3·8TW).

The theoretical annual energy content of the world’s rivers has earlier been estimated

at 36000 TWh (1 terawatt-hour=1×10

kWh); never-

Water power development: low-head Hydropower utilization 9

TABLE 2

WORLD’S HIGHEST DAMS (after T.W.Mermel)

Name Country River Dam

type

Height

(m)

Year of

commissioning

Rogun USSR Vakhsh E/R 335 1985

Nurek USSR Vakhsh E 300 1980

Grand-Dixence Switzerland Dixence G 285 1962

Inguri USSR Inguri A 272 1980

Boruca

Costa Rica Terraba R 267 1990

Vaiont Italy Vaiont A 262 1961

Chicoasén Mexico Grijalva E/R 261 1980

Tehri

India Bhagirathi E/R 261 1990

Alvaro Obregon Mexico Tenasco G 260 1946

Kishau India Tons E/R 253 1985

Sayano-

Shushensk

USSR Yenisei G/A 245 1980

Guavio

Colombia Guavio E/R 243 1987

Mica Canada Columbia E/R 242 1973

Mavoisin Switzerland Drange de

Bagnes

A 237 1957

Chivor Colombia Bata R 237 1975

Chirkey USSR Sulak A 233 1978

Oroville USA Feather E 230 1968

Bhakra India Sutlej G 226 1963

El Cajón Honduras Humuja A 226 1985

Hoover USA Colorado A/G 221 1936

Contra Switzerland Verzasca A 220 1965

Mratinje Yugoslavia Piva A 220 1976

Dworshak USA Clearwater

N.Fork

G 219 1973

Glen Canyon USA Colorado A 216 1966

Taktogul USSR Naryn G 215 1978

Klamm

Austria Dorferbach-

Matrei

A 220 1989

Developments in hydraulic engineering–5 10

Daniel Johnson Canada Manicouagan M 214 1968

Dez Iran Dez A 213 1962

Keba Turkey Euphrates E/G/R 207 1974

Khudoni

USSR Inguri A 201 1990

Kölnbrein Austria Malta A 200 1977

Lower

Tunguska

USSR L.Tunguska E/G 200 1994

Luzzone Switzerland Brennodi L. A 208 1963

San Roque

Philippines Agno E/R 210 1992

Almendra Spain Tormes-Duero A 202 1970

Karun Iran Karun A 200 1976

Planned or under construction.

A=arch, E=earth, G=gravity, R=rockfill.

theless, later assessments reveal values from 44000 up to almost 50000 TWh/a. The

available energy appears in recent inventories on hydropower resources at about 10000

TWh/a.

The estimate of the installable power and, consequently, of producible energy varies

greatly with time, showing an unmistakable increase over the

TABLE 3

WORLD’S LARGEST-CAPACITY

RESERVOIRS (after T.W.Mermel)

Name Country Capacity (10

)

Owen Falls Uganda 2700

Kahkovskaya USSR 182

Bratsk USSR 169

Aswan (High) Egypt 169

Kariba Zimbabwe 160

Akosombo Ghana 148

Daniel Johnson Canada 142

Guri Venezuela 138

Kama USSR 122

Bennett W.A.C. Canada 74

Krasnoyarsk USSR 73

Zeya USSR 68

Water power development: low-head Hydropower utilization 11

Cabora Bassa Mozambique 63

La Grande 2 Canada 62

La Grande 3 Canada 60

Ust Ilim USSR 59

Volga-V.I.Lenin USSR 58

São Felix Brazil 55

Caniapiscau Canada 54

Cerros Colorados Argentina 54

Chapeton

Argentina 54

Shintoyone Japan 54

Upper Wainganga

India 51

Bukhtarma USSR 50

Planned or under construction.

last decades. The tendency of an almost constant growth of available hydropower

resources is partly the outcome of technological progress, but even more so a

consequence of the disillusionment about ‘extremely cheap oil’ and of disappointment

about the too optimisitic assumptions on the energy production costs of other types of

power plants.

In the early 1970s about 10% of the available hydropower resources had been

harnessed. For the end of 1985, a quantity of 2200 TWh/a producible hydroenergy was

anticipated which corresponds to about a 20% rate of exploitation. Summary data on

recent developments in hydropower

and on the largest-capacity projects of the world are

published. Table 4 lists the plants achieving or having a planned capacity of 2500 MW or

more.

The participation of hydroelectricity in world production of electric energy

TABLE 4

LARGEST-CAPACITY HYDROPOWER

PLANTS OF THE WORLD (1985) (after

T.W.Mermel)

Rated capacity (MW) Name Country

1985 Planned

Itaipu Brazil/Paraguay 2800 12600

Guri Venezuela 2800 10000

Tucurui Brazil 3960 8000

Grand Coulee USA 6494 6494

Developments in hydraulic engineering–5 12

Sayano-Shushensk USSR 6400 6400

Corpus

Argentina/Paraguay – 6000

Krasnoyarsk USSR 6000 6000

La Grande Canada 2000 5328

Churchill Falls Canada 5225 5225

Bratsk USSR 4500 4500

Ust-Ilim USSR 3675 4500

Yacyretá-Apipe

Argentina/Paraguay – 4050

Cabora Bassa Mozambique 2000 4000

Rogun

USSR – 3600

Paulo Afonso I Brazil 1524 3409

Ilha Solteira Brazil 3200 3200

Gezhouba P.R. of China 2715 2715

John Day USA 2160 2700

Nurek USSR 900 2700

Revelstoke Canada 900 2700

São Simão Brazil 2680 2680

Mica Canada 1730 2610

Volgograd USSR 2563 2563

Itaparica

Brazil – 2500

Planned or under construction.

shows a diminishing trend: in 1950 it was 35·8%, in 1974 it decreased to 23·0%, in 1985

to 18·4%, and 14% is anticipated for 2000.

3.2 Pumped Storage

Pumped storage plants do not produce additional energy for the network; their operation

is a double-phase power conversion accomplished by recycling of water masses between

two reservoirs. The originally unique objective was to store the surplus energy producible

by any type of power plant in the off-peak periods of the power system, in the form of

hydraulic potential energy, in order to regain it during periods when the peak demand on

the system exceeds the total capacity of the co-operating stations. Thus a pumped storage

project consists of the following main structures: (a) lower basin; (b) power plant which

operates as a pumping station during the off-peak periods and generates power in the

peak-load times; (c) penstock(s) or pressure shaft(s); (d) upper basin with intake

headwork (Fig. 3).

Water power development: low-head Hydropower utilization 13

Coverage of daily, weekly and seasonal (annual) peak demands can be differentiated

according to the selected recycling period. In the earliest stages of development the

pumped storage plants were almost exclusively designed to carry the daily peak loads,

and this is still their most common mode of operation. Up to the 1960s, with few

exceptions, the powerhouses were equipped with three-machine aggregates (pump,

motor/generator, turbine), while in the last decade the achievements in constructing high-

efficiency pump-turbines (reversible hydraulic machines) resulted in the increasing

application of two-machine sets (motor/generator and pump/ turbine).

Experience with pumped storage has shown that, apart from the coverage of peak

power demands, it can considerably contribute to the efficiency and safety of the power

system by some special modes of

FIG. 3. Conceptual sketch of pumped

storage plant.

operation, i.e. by participation in or guidance of the network frequency control, provision

for regular and emergency power reserve and improvement of the network’s power factor

(by synchronous condenser or induction motor operation).

Pumped storage can also be extended to multi-purpose schemes combining the above

described power management with irrigation, potable and industrial water supply, low-

water enhancement for environmental quality control, flood alleviation and recreation

and landscape protection, etc.

Extensive literature is available on pumped storage and its environmental effects. The

proceedings of the international conference on this topic at the University of Wisconsin,

Milwaukee, September 1971, apart from presenting the geotechnical, technological,

Developments in hydraulic engineering–5 14

economical and environmental aspects of planning, design, construction and operation of

both single-purpose and multi-purpose pumped storage schemes, contain an exhaustive

bibliography.

Further references to pumped storage will be given in a future chapter

dealing with high-head developments.

3.3 Tidal Power Generation

In the present stage of technological progress, the utilization of tides for power generation

appears to be most promising (as manifested by profound multi-disciplinary studies).

The tidal amplitude attains considerable magnitudes in certain oceanic regions, e.g. at an

Atlantic coastal stretch of Canada 13·5 m (15 m), in the Bristol Channel 10 m (14 m), on

the French Atlantic coast 8 m (13·5 m), where the first values denote the mean annual

ranges and the figures in brackets refer to the maximum, i.e. equinoctial amplitudes. In

the Pacific region high tides are also recorded, e.g. along the coasts of China and the

USSR, where the utilization of mean annual amplitudes of 6–9 m have been considered.

Recently Wilson and Balls

presented in these volumes a comprehensive discussion of

the present state of the art in tidal power, and it is worthwhile recording here only that the

first high-capacity tidal project in the world, the Rance plant on the French Atlantic coast

equipped with twenty-four 10 MW capacity bulb tubular generating sets, was

commissioned in 1966.

15,16

Although originally economists and engineers doubted the

economic feasibility of this tidal plant, it has been accepted as successful since its energy

production cost makes it competitive with other power resources in the French power

system. This success and further technological developments

14,17

have stimulated the

construction and planning of tidal plants in Canada,

the USSR, China and the UK.

3.4 Wave Energy Conversion

The average power transmitted by a sinusoidal wave on a length of 1 m is

(22)

where γ is the specific weight of the water (9810N/m

), g=9·81 m/s

, H=wave height in

m, T=wave period in s, d=water depth in m, k is the wave number expressed as

This theoretical equation related to a single wave has to be corrected to obtain values

corresponding to a real wave spectrum.

By substituting the constants into eqn (22) and applying some approximations, the

physical (potential) specific wave power may be expressed as

(23)

Water power development: low-head Hydropower utilization 15

It is assumed that about 50% of potential wave energy can be captured and this

convertible power can be further utilized with an efficiency of around 50% (generation

and transmission). Grove-Palmers estimated the electric power producible along a 1000

km long coastline of the UK as high as 12000 MW.

The wave energy converter generally comprises the following main parts: (1)

reference frame (body); (2) mechanical power conversion device; (3) electrical

equipment; (4) power transmission; (5) structural linkage between converter and sea bed.

Several types of converter systems have been studied and proposed for industrial use.

Some are floating devices, while others are rigidly fixed to the sea bed. Since the

technology of wave power utilization is still in statu nascendi, and there is still no general

agreement as to which type from the innumerable proposals will provide the most

economical solution, only a brief summary of some of the devices is given here. Further

details are available in the literature.

19–21

The main categories, named according to the principle of their functioning, are as

follows:

(a) The terminator is a floating device positioned perpendicular to the direction of the

predominating wave flux. The converter incorporates flexible air bags which,

pendulated by waves, induce twodirection air currents in a self-rectifying air turbine,

the latter coupled to a generator (Salter’s Duck, Sea Clam).

(b) The attenuator penetrates into the wave, its axis being parallel to the direction of wave

propagation (Cockerell Raft, Lancaster Flexible Bag, etc.). Thus the power of the

wave is absorbed progressively by the device’s elements as the wave crest moves

along its length.

(d) NEL’s Oscillating Water Column is rigidly fixed to the sea bed. Either a membrane-

closed or an open oscillating water column responds to the oncoming wave and

induces oscillations of air masses which drive the turbines. Figure 4 elucidates the

operation of the rectifying values resulting in a unidirectional airflux through the

turbine.

(e) The Buoy Power Converter is, in contrast to all the above listed ‘linear’ power

converters, a ‘point absorber’. The spherical buoy with an opening at its lower end is

submitted to a heaving motion by the waves generating an air current (Norwegian

solution), or accelerated water masses (Swedish variant) driving the turbine.

The recently published results of the UK research programme do not at present indicate

promising economical results.

3.5 Depression (Solar) Schemes

This possibility of hydropower generation is based on the high potential evaporation in

hot-climate regions with sea water being conveyed through

Developments in hydraulic engineering–5 16

FIG. 4. The NEL breakwater wave

energy converter. This drawing

elucidates the rectifying concept

applied similarly in various other types

of converters. (After G.W.Moody and

G.Elliot.)

a canal or tunnel into a basin below sea level from where it evaporates. The level to

which the depression fills will be determined by the equilibrium between inflow and

evaporation. The relation between the rate of flow Q (m

/s) and evaporating surface A

) and the annual evaporation h (m/a) can be obtained as

(24)

The available head for utilization after reductions due to the conveyance losses pertaining

to any discharge is given by the difference between sea and steady-state lake level. Since

a higher discharge requires a greater evaporation surface (and vice versa), it follows from

the above that the utilizable discharge is in inverse relation to the attainable head. The

powerhouse suitably located at the bank of the (depressed) lake houses the generating

aggregates.

Up to the present, due to the high investment costs, no scheme of this type has been

implemented although several deep natural basins situated in the vicinity of sea coasts

were already identified some decades ago. Two solar projects have been intensively

studied and elaborated as construction-ripe plans:

— The Qattara depression plant in Egypt, to be created by a 75 km long connection

(deep-cut canal and/or tunnel) between the Mediterranean and the depression to be

filled to provide an evaporation surface of 20000 km

; designed for 660 m

/s discharge

and 40 m head.

— The Dead Sea scheme in Israel with an inlet from the Mediterranean through an 80 km

long connection, providing a head of 390 m; the planned plant capacity lies between

100 and 300 MW.

Water power development: low-head Hydropower utilization 17

3.6 Classification of Traditional Hydropower Projects According to

Objectives and Main Physical and Technological Parameters

(1) The turbines can (a) directly drive pumps or other types of machines (in factories,

mines, etc.), or (b) be coupled to generators thus producing electric power. The former

solution belongs more to the past; its application at present is very exceptional.

(Therefore this treatise deals with the hydroelectric mode of utilization only.)

(2) Single-purpose and multi-purpose schemes. The possible secondary objects are:

flood control, irrigation, navigation, industrial and/or municipal water supply, low-water

enhancement, groundwater recharge, drainage, provision for recreation and sporting

facilities, improvement of environmental qualities. In several instances priority is given

to one or more of the above purposes and power generation may be a secondary aim only.

(3) According to the general layout of the entire project the following main

distinctions are made: the power station proper is located (a) in the river, (b) in or at one

end of a diversion (canal, penstock, tunnel).

(4) According to storage the following differentiation is usual. If the dam or river

barrage is very low and the topographical and/or operational constraints allow no or only

an insignificant change in the headwater level the natural discharge Q is utilized by the

turbines up to the plant design flow (plant discharge capacity, plant rated discharge) Q

while during periods when Q>Q

the excess flow Q−Q

has to be released through the

weir (over the spillway). This type of project is termed run-of-river plant. When the

available storage capacity and the permissible change in headwater elevation render

possible a small-scale discharge control so that the plant can contribute to the daily peak

power production, the term pondage is used. Reservoirs with relatively (to the integrated

natural flow) large capacities can provide (a) for generation of weekly, seasonal or annual

peak energy, or (b) for partial or complete equalization of long period inflows. Thus

weekly, seasonal, yearly and multi-annual storages can be distinguished.

(5) The attributes open-air and underground solution refer to the location of the

powerhouse (machine hall) of the project.

(6) Plants are sometimes characterized according to their installed power capacities:

high capacity, medium capacity, low capacity, etc. Such specification, of course, has not

proved realistic, for this type of valuation strongly depends on the existing hydropower

site potentials in the various river basins and countries. During recent years extraordinary

world-wide interest has been focused on the so-called ‘small hydro’. This type of plant

(also named small-scale or mini plant) cannot be defined unequivocally, i.e. with a fixed

power limit, either. However, a separate analysis of the very-low-power plants is justified

because they require specific treatment in design and implementation. According to

diverse suggestions the capacity of typical small plants could be limited by 1 to 5 or even

15 MW. (It is not the capacity but the specific features, if any, of the small plant that

matter.)

(7) According to the order of magnitude of the utilizable net head for the turbines it is

customary to differentiate between low-head and high-head plants. (Previously some

authors suggested a three-stage grouping by discerning medium-head developments too.)

This presentation is based on the separation of low-head and high-head projects, in spite

of the fact that it is difficult to define an unequivocal limit with a fixed figure concerning

the head. Therefore, it seems to be more appropriate to describe the main characteristics

of the two types.

Developments in hydraulic engineering–5 18

Novak P. Developments in hydraulic engineering - Vol. 5

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