Hydroelectric power plant (HPP) is a power plant that uses energy of water masses as a source of energy in channel waterways and tidal movements. Hydroelectric power plants are usually built on rivers, constructing dams and reservoirs. Two main factors are necessary for effective power generation at HPPs: guaranteed availability of water all year round and possibly large slopes of the river, cune-like reliefs favor hydropower construction.
The principle of operation of the hydropower station is quite simple. The chain of hydraulic structures provides the necessary pressure of water flowing on the turbine blades, which drives the generators that produce electricity.
The necessary pressure of water is formed through the construction of a dam, and as a consequence of the concentration of the river in a certain place, or derivation - a natural flow of water. In some cases, in order to obtain the necessary pressure of water, both the dam and the derivation are used together.
Directly in the building of the hydroelectric power station is located all the power equipment. Depending on the purpose, it has its own specific division. In the engine room are hydroelectric units that directly convert the energy of the water flow into electrical energy. There are all kinds of additional equipment, control devices and control over the operation of the HPP, a transformer station, switchgears and much more.
Hydroelectric stations are divided depending on the power output:
- Powerful - produce from 25 MW and higher;
- Medium - up to 25 MW;
- small hydroelectric power stations - up to 5 MW.
The power of the hydropower plant depends on the head and water flow, as well as on the efficiency of the turbines and generators used. Due to the fact that according to natural laws the water level is constantly changing, depending on the season, and also for a number of reasons, it is customary to take the cyclic power as an expression of the power of the hydroelectric station. For example, distinguish between the annual, monthly, weekly or daily cycles of the hydroelectric plant.
Hydroelectric power stations are also divided according to the maximum use of the water head:
- high-pressure - more than 60 m;
- medium-pressure - from 25 m;
- low pressure - from 3 to 25 m.
Depending on the pressure of water, hydroelectric power plants use different types of turbines. For high-pressure - bucket and radial-axial turbines with metal spiral chambers. Rotary-blade and radial-axial turbines are installed at medium-pressure hydropower plants, and rotor-bladed turbines in reinforced concrete chambers are mounted on low-pressure turbines.
The principle of operation of all types of turbines is similar - the flow of water enters the turbine blades, which begin to rotate. The mechanical energy is thus transferred to a hydrogenerator, which generates electricity. Turbines differ in some technical characteristics, as well as chambers - steel or reinforced concrete, and are designed for a different head of water.
Hydroelectric stations are also divided, depending on the principle of the use of natural resources, and, accordingly, the formed water concentration. The following HPPs can be identified here:
- dam hydroelectric power stations. These are the most common types of hydroelectric stations. The water pressure in them is created by installing a dam that completely encloses the river, or raising the water level in it to the required mark. Such hydroelectric power stations are built on the highland lowland rivers, as well as on mountain rivers, in places where the riverbed is narrower and narrower.
- dam-hydroelectric power stations. Are built at higher headings of water. In this case, the river is completely blocked by the dam, and the building of the HPP is located behind the dam, in the lower part of the dam. Water, in this case, is fed to turbines through special pressure tunnels, and not directly, as in channel hydroelectric power stations.
- derivational power plants. Such power plants are built in those places where the slope of the river is great. The necessary concentration of water in this type of HPP is created through derivation. Water is diverted from the river bed through special drainage systems. The latter are straightened, and their incline is much smaller than the average deviation of the river. As a result, water is supplied directly to the building of the HPP. Derivational hydropower plants can be of different types - non-pressure or with pressure derivation. In the case of pressure derivation, the water conduit is laid with a large longitudinal slope. In another case, at the beginning of the derivation a higher dam is created on the river, and a reservoir is created - this scheme is also called mixed derivation, since both methods of creating the necessary water concentration are used.