Hydroelectric Power Plant

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Hydroelectric Power Plant


a complex of installations and equipment that is used to convert the energy of a stream of water into electrical energy. A hydroelectric power plant consists of a sequential chain of hydraulic-engineering facilities that provide the necessary concentration of water flow and create a head, as well as power-generating equipment for transforming the energy of water moving under pressure into the mechanical energy of rotation, which in turn is transformed into electrical energy.

The pressure at hydroelectric power plants is created by

Figure 1. Diagram of the concentration of river drop by a dam

concentrating the drop in a river on the sector being developed (ab) through a dam (Figure 1), by a diversion (Figure 2), or by a combination of the two (Figure 3). The main power-generating equipment at a hydroelectric power plant is located in the powerhouse; the hydraulic units, auxiliary equipment, and automatic control and supervision equipment are located in the machine room; and the operator-dispatcher’s panel or the automatic operator are at the central control station. A step-up transformer substation can be located either within the powerhouse or in separate buildings or open areas. Distribution facilities are often situated in open areas. The power plant can be divided into sections with one or more units and auxiliary equipment; these sections are separated from neighboring parts of the building. Beside or within the power plant building is an assembly area for assembling and repairing various equipment and for auxiliary operations for servicing the plant.

Figure 2. Diagram of the concentration of river drop by a diversion

Hydroelectric power plants are rated as large (more than 250 megawatts [MW]), medium (up to 25 MW), and small (up to 5 MW) in terms of rated capacity. The capacity depends on the pressure Pd (the difference between the levels of the headrace and tail water), the discharge of water Q (cu m per sec) used in the hydraulic turbines, and the efficiency ŋu of the hydraulic unit. For a number of reasons (for example, because of seasonal fluctuations in water level in reservoirs, irregular demands on the power system, and repairs to hydraulic equipment or hydraulic-engineering installations), the water head and discharge are constantly changing and, in addition, the discharge changes during regulation of the power of the plant. Annual, weekly, and diurnal cycles of operation are distinguished.

On the basis of maximum utilized head, power plants are classified as high-head (more than 60 m), medium-head (25-60 m) and low-head (3-25 m). For plains rivers, heads rarely exceed 100 m, but in the mountains, dams can be used to create pressures up to 300 m and more, and by using diversions, the head can be raised to 1,500 m. Classification according to pressure approximately corresponds to the types of generating equipment used: in high-pressure plants, impulse and radial-axial turbines with metal spiral chambers

Figure 3. Mixed diagram of the concentration of river drop by a dam and a diversion

are used; in medium-pressure plants, adjustable-blade and radial-axial turbines with reinforced-concrete and metal spiral chambers are used; and in low-pressure plants, adjustable-blade turbines in reinforced-concrete spiral chambers, and sometimes horizontal turbines in capsules or open chambers, are used. The classification of hydroelectric power plants on the basis of the head used is approximate and arbitrary.

In terms of type of utilization of water resources and concentration of pressures, hydroelectric power plants are usually classified as channel, dam, diversion (with pressured or nonpressured diversion), mixed, pumped-storage, and tidal types. In the channel and dam types, a head of water is created by a dam that blocks the river and raises the water level upstream. This inevitably involves some flooding of the river valley. If two dams are built on the same stretch of a river, less land is inundated. On plains rivers the height of a dam is limited by the greatest economically feasible area of flooded land. Channel and dam hydroelectric power plants are built both on high rivers in plains areas and in narrow constricted valleys on mountain streams.

In addition to the dam, the complex of facilities at a channel power plant includes the power plant building and overflow installations (Figure 4). The aggregate of hydraulic engineering

Figure 4. Cross section of the powerhouse of the Volga Twenty-second Congress of the CPSU Hydroelectric Power Plant: (1) water intake, (2) turbine chamber, (3) hydroturbine, (4) generator, (5) suction pipe, (6) distribution devices (electric), (7) transformer, (8) gantry cranes, (9) machine-room crane, (10) bottom weir

works depends on the size of the head and the rated capacity. At a channel power plant, a building with hydraulic-engineering units inside is an extension of the dam and at the same time creates a head of pressure. In this case, the power plant building is adjoined by the headrace on the one hand and the tail water on the other. The spiral chambers leading to the hydraulic turbines are mounted with intakes below the level of the headrace, and the conduits leading from the turbines are mounted below the level of the tail water.

A hydroelectric power plant may include, depending on its purpose, navigable locks or a ship elevator, fish ladders, or water-intake works for irrigation and water supply. In channel power plants, the power plant building is sometimes the only installation through which water passes. In such cases the usable water regularly passes through an intake aperture with gratings to trap trash, a spiral chamber, the hydraulic turbine and the exit conduit; special water conduits situated between adjoining turbine chambers handle excess floodwaters. Channel power plants have heads of 30-40 m; low-capacity rural plants built earlier are among the simplest channel-type plants. On large plains rivers, the main channel is blocked by an earth-fill dam, which is adjoined by a concrete overflow dam and a power-plant building. Such a combination is typical of many Soviet power plants on major plains rivers. The Volga Twenty-second Congress of the CPSU Hydroelectric Power Plant is the largest of the channel-type plants.

At larger heads the transmission of the hydrostatic pressure of the water to the power-plant building is not feasible. In this case, a dam-type plant is used in which the pressure front is covered by the dam over its entire length, and the power plant building is situated behind the dam and adjoins the tail water (Figure 5). The hydraulic course between the headrace and tail water of the power plant includes a submerged intake with a grid to catch refuse, a turbine penstock, a spiral chamber, a hydraulic turbine, and a discharge conduit. Navigation facilities and fish ladders, as well as an extra spillway, can be additional structures in the power plant complex. The Bratsk Hydroelectric Power Plant on the Angara River is an example of such a plant.

Figure 5. Diagram of the Saian Hydraulic-engineering Complex

Another type of arrangement for a power plant at a dam, which corresponds to mountainous conditions and rivers with relatively little water, is found at the Nurek Hydroelectric Power Plant on the Vakhsh River (Middle Asia), with a projected capacity of 2,700 MW. The power plant building is open and is situated below the dam. Water is brought to the turbines by one of several pressure tunnels. Sometimes the power plant building is placed closer to the headrace in an underground excavation (underground hydroelectric power plant). Such an arrangement is practical where there is a bedrock base, especially with earth-fill or rubble dams of considerable width. Floodwaters are handled through spillway tunnels or through open spillways on the banks.

In diversion power plants, the drop in water is concentrated by a diversion. At the beginning of the section of the river that is being used, the water is diverted from the river by a conduit whose gradient is considerably less than the gradient of the river on that section and which also has fewer twists and turns. The diversion conduit terminates at the power plant building. The used water is either returned to the river or sent on to another diversion power plant. Diversion is advantageous only when the river’s gradient is large. A diversion system for concentrating pressure in pure form (an intake without a dam or with a low intake dam) in actual practice means that only a small amount of the water available is drawn from a river. In other instances, a higher dam is built and a reservoir is formed at the intake. Such a scheme for concentrating the gradient is called a mixed system, since it uses both principles for developing a head. Sometimes, depending on local conditions, it is more advantageous to situate the power plant building at some distance from the upstream section of the river, in which case the diversion system is in two parts with relation to the power plant building: one part brings water to the building, and the other carries it away. In some cases a diversion is used to shift a river’s flow into a neighboring river that has lower channel characteristics. The Inguri Hydroelectric Power Plant is a typical example: the flow of the Inguri River is diverted by a tunnel into the neighboring Eristskali (Caucasus) River.

The facilities at nonpressured diversion power plants consist of three main groups: water-intake works, a water-storage dam, and the diversion itself (a canal, a race, and a nonpressured tunnel). Additional structures at a power plant with nonpressured diversion are stilling basins and pools for diurnal control of operations, pressure basins, and extra spillways and turbine penstocks. The largest hydroelectric power plant with nonpressured intake diversion is the Robert Moses Hydroelectric Power Plant (USA), with a capacity of 1,950 MW; the largest with a nonpressured outlet diversion is the Inguri Hydroelectric Power Plant (USSR), with a capacity of 1,300 MW.

At hydroelectric power plants with pressured diversion, the conduit (tunnel or metal, wooden, or reinforced-concrete pipe) is laid with a somewhat greater longitudinal gradient than in the case of nonpressured diversions. A pressure intake diversion is used because of fluctuations in the water level in the headrace, which also cause changes in the internal pressure of the diversion during operations. The facilities for a power plant of this type include a dam, a water-intake complex, a diversion and pressure penstock, the station section of the plant, including a control reservoir and turbine penstocks, and an outlet diversion in the form of a canal or tunnel (in the case of an underground powerhouse). The largest hydroelectric power plant with a pressure intake diversion is the Nechako-Kemano plant (Canada), which has a projected capacity of 1,792 MW.

A hydroelectric power plant with outlet diversion is used under conditions where there are considerable fluctuations in water level in the river at the diversion outlet, or for economic reasons. In this case it is necessary to build a leveling reservoir (at the beginning of the diversion) to equalize the unstable flow of water in the river. The largest plant of this type is the Harsprânget Hydroelectric Power Plant (Sweden) with a capacity of 350 MW.

Pumped-storage power plants and tidal power plants occupy a special place among hydroelectric power plants. The construction of a pumped-storage plant is based on increased demand for peak capacity in large power systems, which in turn determines the generator capacity needed to cover peak loads. The ability of a pumped-storage system to accumulate power is based on the fact that during a certain period of time (a drop in the demand schedule), excess electric power is used by the power plant equipment in a pumping system to drive water from a reservoir into a higher storage basin. During peak load periods, the power thus accumulated is returned to the energy system—water from the upper basin enters a turbine penstock and drives hydroelectric units that are operating in the current-generating mode. The capacity of individual storage systems with such reversible generator equipment may be as high as 1,620 MW (Cornwall, USA).

Tidal power plants convert the energy of sea tides into electrical energy. In view of certain peculiarities involved in the periodic nature of tides, the electrical energy of tidal power plants can be used in energy systems only in conjunction with the energy of regulating power plants, which supplement shortages in capacity over a period of days or months. Work on a major tidal power plant was completed on the Rheims River in France in 1967 (24 units with total capacity of 240 MW). The first experimental tidal power plant in the USSR went into operation at Kislaia Guba (Kola Peninsula) in 1968. It has a capacity of 0.4 MW, and experimental work is now in progress for construction of future tidal power plants.

Depending on the type of water use and operating conditions, a distinction may be made among hydroelectric power plants that operate on normal discharge without regulation and those that have diurnal, weekly, seasonal (annual), or long-term regulation. Some plants or power grids operate, as a rule, in a system together with condensation, steam, and atomic power plants and gas-turbine installations. Depending on the role played in covering the load schedule of a power system, one can divide hydroelectric power plants into basic, semipeak, or peak.

A major feature of hydraulic power resources in comparison with fuel resources is the fact that they are constantly replenished. The absence of a fuel requirement for hydroelectric power plants results in reduced prime cost of the power produced by such a plant. For this reason, although considerable unit capital investment per kilowatt of rated capacity is required for hydroelectric power plant construction, and although construction work lasts a long time, great importance has been—and is—attached to hydroelectric power plant construction, especially when it is linked to the location of power-consuming production processes.

Some of the first hydroelectric power installations, which had capacities of only a few hundred watts, were built in 1876-81 in Laufen (Germany) and Greyside (England). The development and industrial use of hydroelectric power plants are closely related to the problem of transmitting electric power over large distances: as a rule, the locations that are most favorable for building power plants are remote from the principal consumers of electrical energy. The electric transmission lines at that time did not exceed 5-10 km; and the longest was 57 km. The construction of a 170-km transmission line from the Laufen Power Plant to Frankfurt am Main (Germany) to supply electricity to the International Electrical Engineering Exposition (1891) opened up wide vistas for the development of hydroelectric power plants. In 1892 industrial current was supplied by a hydroelectric plant built on a waterfall at BÜlach (Switzerland), and almost at the same time—in 1893—plants were built at Helsen (Sweden), on the Isar River (Germany), and in California (USA). The Niagara Power Plant (USA) began to produce direct current in 1896, the Reinfeld Power Plant (Germany) produced current in 1898, and the generators at the Jonte Power Plant (France) went into operation in 1901.

In Russia, detailed plans for hydroelectric power plants had been drawn up by the Russian scientists F. A. Pirotskii, I. A. Time, G. O. Graftio, and I. G. Aleksandrov, but they were not carried out. These plans envisaged, in particular, the use of the rapids of the Dnieper, Volkhov, Zapadnaia Dvina, and Vuoksa rivers. Thus, for example, as early as 1892-95, the Russian engineer V. F. Dobrotvorskii drew up plans for construction of a 23.8-MW plant on the Narova River and a 36.8-MW plant at the Bol’shoi Imatra waterfall. These plans were thwarted both by the inertia of the tsarist bureaucracy and the interests of private capitalist groups associated with the fuel industry. The first industrial hydroelectric power plant in Russia, with a capacity of about 0.3 MW (300 kW) was built in 1895-96 under the direction of Russian engineers V. N. Chikolev and R. E. Klasson to supply electricity to the Okhta Powder Works in St. Petersburg. In 1909 work was completed on the Hindu Kush Power Plant, which was the largest in prerevolutionary Russia. It had a capacity of 1.35 MW (1,350 kW) and was built on the Murgab River in Turkmenia. The low-capacity Satka, Alaverdy, Karakultuk, Turgusun, and Sestroretsk power plants went into operation between 1905 and 1917. Power-generating facilities using the equipment of foreign firms were also built at private mills and factories.

World War I (1914-18) and the related intensive growth of industry in some Western countries resulted in the development of existing power-industry centers and the construction of new centers, including those based on hydroelectric power plants. As a result, the capacity of hydroelectric power plants throughout the world reached 17,000 MW by 1920, and the capacity of individual plants, such as Muscle Shoals (USA) and IIe Maligne (Canada), was in excess of 400 MW (400,000 kW).

The total capacity of hydroelectric power plants in Russia by 1917 was about 16 MW; the largest plant was the Hindu Kush plant. The construction of large hydroelectric power plants began in earnest only after the Great October Socialist Revolution. In the period of reconstruction (the 1920’s), in accordance with GOELRO (State Commission for the Electrification of Russia), the first large hydroelectric power plants were built—the Volkhov (now the Volkhov V. I. Lenin Hydroelectric Power Plant) and the Zemo-Avchal’skaia V. I. Lenin Hydroelectric Power Plant. The Dnieper, Nizhniaia Svir’, and Rioni hydroelectric plants went into operation during the first five-year plans (1929-40).

Thirty-seven hydroelectric power plants with a total capacity of more than 1,500 MW had gone into operation by the beginning of the Great Patriotic War (1941-45). During the war work was stopped on a number of plants, with a total capacity of about 1,000 MW (1 million kW). A considerable number of plants, with a total capacity of about 1,000 MW, were destroyed or dismantled. Construction was started on new low- and medium-capacity hydroelectric plants in the Urals (Shirokovskii, Verkhotur’e, Alapaevsk, and Be-loiarsk), Middle Asia (Akkavak, Farkhad, Salarskaia, and Nizhnii Buesui), the Northern Caucasus (Maikop, Ord-zhonikidze, and Krasnaia Poliana), Azerbaijan (the Min-gechaur Hydroelectric Power Plant), Georgia (the Chi-takhevi Hydroelectric Power Plant), and Armenia (the Giumush Hydroelectric Power Plant). By the end of 1945 the capacity of all hydroelectric power plants in the Soviet Union, including those that had been restored, reached 1,250 MW, and annual generation of electrical energy reached 4.8 billion kW-hr.

In the early 1950’s construction was begun on large hydroelectric power plants on the Volga River at the cities of Gorky, Kuibyshev, and Volgograd, on the Kakhovka and Kremenchug Hydroelectric Power Plants on the Dnieper, and on the Tsimliansk Hydroelectric Power Plant on the Don. The Volga V. I. Lenin and Twenty-second Congress of the CPSU hydroelectric power plants became the first of several that are the largest plants in the USSR and in the world. In the second half of the 1950’s work began on the Bratsk Hydroelectric Power Plant on the Angara River and the Krasnoiarsk Hydroelectric Power Plant on the Enesei River. Sixty-three plants with a total capacity of 9,600 MW were built or restored from 1946 through 1958. During the 1959-65 seven-year plan 11,400 MW of new hydroelectric capacity went into operation, and the total capacity of hydroelectric power plants reached 22,200 MW (see Table 1). As of 1970, construction was under way in the USSR on 35 industrial hydroelectric power plants (with a total capacity of 32,000 MW), including 11 with individual capacities in excess of 1,000 MW: the Saian-Shusha, Krasnoiarsk, Ust’-Ilimsk, Nurek, Inguri, Saratov, Toktogul, Nizhniaia Kama, Zeia, Chirkei, and Cheboksary.

The 1960’s saw a tendency to reduce the role of hydroelectric power plants in the total world production of electrical energy and the ever-increasing use of hydroelectric power plants to cover peak loads. By 1970 all the hydroelectric power plants in the world produced about 1 trillion kW-hr of

Table 1. Development of hydroelectric power plants in the USSR for the period 1965-80
1 Forecast
Rated capacity (MW)...............22,20032,00050,00074,500
Share of hydroelectric power plants in total capacity of power plants in USSR (percent)...............19.318.62020.3
Annual power output (billion kW-hr)...............81.4121182260
Share of hydroelectric power plants in electric-power output of USSR (percent)...............16.11615.614.6
Capacity of pumped-storage plants (MW)...............301,4105,100

electricity per year, but beginning in 1960 the ratio of worldwide electricity production by hydroelectric power plants has been decreasing by an average of about 0.7 percent per year. The ratio of electricity produced by hydroelectric plants to total production has dropped especially rapidly in countries traditionally considered to be “hydroelectric” (Switzerland, Austria, Finland, Japan, Canada and, to some extent, France), because their potential for economical hydroelectric generation has been virtually exhausted.

Despite the reduced role of hydroelectric power plants in total production, the absolute figures for energy production and hydroelectric capacity are continually growing because of the construction of large new plants. More than 50 hydroelectric power plants with capacities of 1,000 MW or more each were in operation or under construction in the world in 1969, and 16 of these were in the Soviet Union. (See Table 2.)

Table 2. Largest hydroelectric power plants in the world
Year operation began
1 The capacity of the plants is given as of Jan. 1, 1969; design capacities are given in parentheses
In operation Krasnoiarsk (USSR)...............5,000
Bratsk (USSR)...............4,100
Volga Twenty-second Congress of the CPSU (USSR)...............2,5301958
Volga V. I. Lenin (USSR)...............2,3001955
John Day (USA)...............2,160
Grand Coulee (USA)...............1,974
Robert Moses (Niagara) (USA)...............1,9501961
St. Lawrence (Canada-USA)...............1,8241958
Aswan High Dam (Egyptian Arab Republic)...............1,750
Beauharnois (Canada)...............1,6391948
Under construction
Saian-Shusha (USSR)...............
Churchill Falls (Canada)...............4,500
Usy’-llimsk (USSR)...............4,320
Ilha Solteira (Brazil)...............3,200
Nurek (USSR)...............2,700
Portage Mountain (Canada)...............2,300
Iron Gate (Rumania-Yugoslavia)...............2,100
Tarballa (Pakistan)...............2,000
Mica (Canada)...............2,000

The further development of hydroelectric construction in the USSR envisages the construction of power grids and the integrated use of water resources to meet simultaneously the needs of power engineering, water transportation, water supply, irrigation, and fisheries. The Dnieper, Volga-Kama, Angara-Enisei, and Sevan power grids are examples.

Until the 1950’s the most important area of hydroelectric construction in the USSR was traditionally the European part of the Union, which was responsible for about 65 percent of the electricity produced by all hydroelectric power plants in the USSR. Modern hydroelectric construction is marked by continued construction and improvement of low-and medium-head plants on the Volga, Kama, Dnieper, and Daugava rivers, the construction of large high-head plants in remote regions of the Caucasus, Middle Asia, and Eastern Siberia, the construction of medium and large diversion plants on mountain rivers with large gradients, and the diversion of streams into neighboring basins. Most important, however, is the construction of high-capacity plants on the major rivers of Siberia and the Far East—the Enisei, Angara, and Lena. The hydroelectric plants under construction in regions of Siberia and the Far East that are rich in hydroelectric resources, together with thermal power plants operating on local organic fuel (natural gas, coal, and oil) will become the main energy base for supplying cheap electric power to the developing industry of Siberia, Middle Asia, and the European part of the USSR.


Argunov, P. P. Gidroelektrostantsii. Kiev, 1960.
Denisov, I. P. Osnovy ispol’zovaniia vodnoi energii. Moscow-Leningrad, 1964.
Energeticheskie resursy SSSR. [vol. 2:] Gidroenergeticheskie resursy. Moscow, 1967.
Nikitin, B. I. Energetika gidrostant sii. Moscow, 1968.
Elektrifikatsiia SSSR: 1917-1967. Edited by P. S. Neporozhnyi. Moscow, 1967.
Trudy Gidroproekta: Sbornik 16. Moscow, 1969.
Gidroenergetika SSSR: Statisticheskii obzor. Moscow, 1969.


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