Pumped-Storage Hydroelectric Power Plant

a hydroelectric power plant whose operating principle (storage) consists in the conversion of the electric power received from other power plants into the potential energy of water; during the reverse conversion this stored energy is fed into the power system, mainly to cover peak-load periods.

The hydraulic-engineering installations of a pumped-storage hydroelectric power plant consist of two basins, located at different levels, and a connecting pipe. The hydroelectric units installed in the powerhouse at the lower end of the conduit pipe may consist of three machines connected to a single shaft (a reversible electric motor-generator, a hydroelectric turbine, and a pump) or two machines (a reversible electric motor-generator and a reversible hydroelectric turbine which, depending on the direction of its rotation, may operate as either a pump or a turbine). In the late 1960’s the more economical two-machine units began to be installed at newly commissioned pumped-storage plants.

The electrical energy produced by underloaded power plants of an energy system (mainly during the nighttime hours) is utilized by a pumped-storage power plant to pump water from its lower body of water to the upper storage basin. During peak-load periods water from the upper basin is supplied through the conduit pipe to the hydroelectric units of the pumped-storage plant, which are connected with the operation of the turbine system; the electric power thus generated is fed into the grid of the power system, and the water is stored in the lower basin. The amount of stored electrical energy is determined by the volume of the basins and the effective head of the plant. The upper basin of the plant may be man-made or natural (for example, a lake); the lower basin is frequently a body of water formed by the damming of a river. One of the merits of pumped-storage plants is that they are not subject to the effect of seasonal flow variations. Depending on the height of the head, the hydroelectric units of pumped-storage plants may be equipped with reversible-blade, diagonal, radial-axial, or bucket-type hydro turbines. The time required to start and change the operational system of a pumped-storage plant is several minutes, which determines their high flexibility in use. Based on the very principle of its operation, the regulating range of a pumped-storage plant is close to twice its rated capacity, which is one of its main advantages.

The capability of pumped-storage plants to cover peak loads and to increase the demand for electric power during the nighttime hours makes them an effective means for equalizing the operational schedule of a power system, and in particular those of large steam-turbine power units. Pumped-storage plants may be operated and regulated on complete daily, weekly, or seasonal alternations. High-capacity plants that are built on a rock foundation and have a head of several hundred meters are the most economical. The total efficiency of a pumped-storage plant under optimum design operating conditions approaches 0.75; under actual conditions the average efficiency value, taking into consideration losses in the electrical network, does not exceed 0.66.

The construction of pumped-storage plants close to centers of electric power consumption is feasible, since the installation of long power transmission lines for short-term utilization is not economically possible. The time required to build a pumped-storage plant is usually about three years.

Several plans have been developed in the USSR for the construction of pumped-storage plants in the European part of the country, including the Moscow region; the first plant with reversible hydroelectric units, with a total capacity of 200 megawatts (MW; 200,000 kW), was under construction in 1971 in the zone of the headrace of the Kiev Hydroelectric Power Plant. Also in 1971, pumped-storage plants were under construction in the Federal Republic of Germany, the USA, Great Britain, Austria, France, Japan, and the German Democratic Republic. Among the largest operating pumped-storage plants abroad are the following: Crewkerne (Great Britain)—400 MW, with a head of 440 m, put into commission in 1966; Taum Sauk (USA)—350 MW, in two units of 175 MW each, with a head of 253 m (1963); Hohenwarte II (GDR)—320 MW, with a head of 305 m (1965); and Vianden (Luxembourg)—900 MW, with a head of 280 m (1964). By 1970 the total capacity of pumped-storage plants throughout the world exceeded 15 gigawatts (15 million kW).