Hydraulic structures of micro hydroelectric power plants. Encyclopedia of radio electronics and electrical engineering

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All types of hydroelectric power plants include hydraulic structures, hydromechanical и electrical equipment. Hydraulic structures serve to create conditions for the functioning of the electromechanical equipment of the HPP and include (depending on the type and layout of the HPP) a water intake structure; diversion channel; pressure basin and pipeline; devices for protection against debris and ice; dam; spillway and more. Electromechanical equipment converts water energy into electrical energy and includes a hydraulic unit (hydro turbine and hydro generator), water and electrical control units.

The water intake is designed to divert the required volume (flow) of water from the main river channel into the diversion canal or immediately into the pressure basin (Fig. 12). In addition to ensuring an uninterrupted supply of water to the hydraulic unit in the right amount and at the right time, it protects against the ingress of ice, sludge, sediment, etc.

Slush is loose accumulations of ice, before ice formation, when water cools below 0°C. Depending on the amount of ice, the sludge retains the ability to flow like water or loses this ability due to blockages. With any amount of sludge in water, its fluidity decreases. With a large amount of sludge, the living section of the river can become clogged, which will lead to a significant accumulation of sludge. As a result, the water level may rise. Sludge creates significant difficulties in the operation of hydraulic structures, clogging the intake heads of water intakes, which have to be cleaned and heated.

Fig.12. Scheme of the water intake structure

Fig.12-1. Water intake structure of a micro hydroelectric power station in the village of Balbay, Tyup district

It is very important that the water intake function at all levels of water flow, from the lowest to the flood level. It must also protect the equipment of micro hydroelectric power plants from silt, sand, gravel or other debris brought by the current. The correct water intake design is a decisive factor for the functioning of the entire micro hydropower plant.

The diversion channel is used to supply water from the intake structure to the penstock (Fig. 13 and 13-1). The channel must have a slope along its entire length to ensure the natural flow of water. The diversion channel can be of any length - from zero (if the pressure pipeline starts from the water intake) to several kilometers.

Most economically viable diversion canals are open canals, as they can be built with a low slope and a large cross section and therefore result in low water pressure losses.

Fig.13. The diversion canal of a micro hydroelectric power station in the village of Balbay village, Tyupsky district Balbay, Tyupsky district (view of the water intake facility)

Fig.13-1. Diversion canal of a micro hydroelectric power station in the village of Balbay village, Tyupsky district Balbay, Tyupsky district (view of the pressure basin)

The pressure basin is used to uniformly supply water to the pressure pipeline (Fig. 14 and 14-1). It ensures that the pressure pipeline is flooded with water (to avoid air entrapment and, accordingly, water hammer on the turbine) and the mode of water supply to the pipeline - by regulating the changing volume of water flow. The water in the pressure basin should be calm, without breakers and eddies. The pressure pipe opening must always be flooded with water (the minimum distance from the pressure pipe opening to the upper water mark must be at least 30-40 cm).

Water hammer (water hammer) is a pressure surge in a pressure pipe caused by a rapid change in the flow rate of water in a very short period of time. It can occur due to a sudden closing or opening of the valve, as well as the capture of air from the pressure basin or discharge path. Water hammer can damage a hydro turbine, pipeline or other elements of a hydroelectric power station.

Fig.14. Pressure basin scheme (plan)

Fig.14-1. Scheme of the pressure basin (section)

The following are installed in the pressure basin: a trash grate (to protect the turbine from debris, stones, branches, etc.); a gate for regulating the water supply to the pressure pipeline and a gate for discharging water and bottom sediments. The size of the forebay is usually determined based on the specifications of the turbine.

Fig.15. Pressure basin of the former HPP Pioner, Ak-Suu district, Issyk-Kul region.

The pressure pipeline serves to supply water from the pressure basin to the hydraulic unit (Fig. 16). It can be metal, asbestos-cement, plastic, wood. The diameter of the pipeline must strictly correspond to the flow of water. The pressure pipeline can be buried in a trench, laid on the ground or placed on supports.

Fig.16. Main components of a micro hydro power plant

Some designs of micro HPPs provide for the installation of a surge tank on the pressure pipeline (Fig. 17) to mitigate possible water hammer. It is advisable to place the surge tank closer to the hydraulic unit; in this case, there is less pressure during hydraulic shock, but at the same time it is necessary to install the tank at a higher height, which can increase the cost of the structure.

Fig.17. Surge tank diagram

The outlet channel is designed to divert water from the outlet tract back to the river. The place where the water flows into the river must be reinforced with concrete or stone to prevent erosion of this place. In some cases (depending on the design of the HPP), at the outlet of the waste water from the outlet duct, it is necessary to construct a damper (Fig. 18), which creates the necessary water backwater for:

• protection against reverse water hammer (air ingress from the outlet tract into the turbine chamber);
• operation of the suction pipe in some HPP designs;
• reducing the useless kinetic energy of the waste water and protecting the outlet channel from being washed away by water.

The extinguisher can be made or built from reinforced concrete or rubble concrete, as well as from improvised materials (stones, etc.).

Authors: Kartanbaev B.A., Zhumadilov K.A., Zazulsky A.A.

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