The main issues of the construction of micro hydroelectric power plants. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Alternative energy sources

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The project for the construction of a micro hydroelectric power station depends on many parameters - hydrotechnical, natural, on the type and complexity of the equipment used, on the conditions of electricity consumption and other factors.

As a rule, if it is planned to install a micro hydroelectric power station with a capacity of up to 10 kW and natural conditions do not require the construction of complex hydraulic structures, then there is no need to attract specialists for design. A plant that manufactures such micro hydroelectric power plants often includes in the delivery, in addition to the hydroelectric unit itself, a flexible (hose) pressure pipeline made of various materials (Fig. 39). In this case, it is enough to make a small water intake, connect a pressure pipeline to it, or additionally build a small diversion canal and a pressure basin.

If it is planned to build a micro HPP of greater capacity, then in this case it is more expedient to invite specialists (or a specialized contractor organization) with the appropriate qualifications and experience for the design and construction of a micro HPP. To choose the right contractor, it will be useful to familiarize yourself with his qualification documents (Gosarchstroy licenses for the construction of hydroelectric power plants or construction work), with previously completed work (designed or built micro hydroelectric power plants). If there is such an opportunity, you can personally see these objects, talk with their owners or users, find out practical issues or difficulties in construction and operation.

Fig.39. Micro HPP of sleeve type

When building a micro HPP with an installed capacity of, for example, more than 10 kW, in addition to the issue of equipment cost, it is necessary to realistically assess your technical and labor capabilities and resources, materials that will be used for the construction of a water intake facility, a diversion canal, a pressure basin, a supporting foundation under equipment. These structures, in addition to the requirements for materials, have fairly strict requirements for size, method of manufacture and construction.

It is also very important to consider the issue of access roads to the construction site - for the transport of building materials, machinery and equipment. Building even a simple technical road or clearing the area of ​​stones and trees, leveling the surface, can significantly increase the cost and complicate the construction of a micro hydroelectric power station.

Water intake

The purpose of a water intake is to take water from a river or reservoir and deliver it to a pressure pipeline. The main requirement is that the intake must function at all flow levels, from the lowest (low water) to the level of floods, from time to time to cope with a large amount of gravel, stones or other debris brought by the current - from leaves and debris to entire trees.

The correct design for water intake is a decisive factor for the proper functioning of the entire hydroelectric power plant and an important condition for reducing the cost of its operation and repair.

The water intake must comply with the following parameters:

• be durable and reliable in order to exclude damage to the structure by floods, mudflows or brought debris, and ensure long-term operation;
• be equipped with various devices and mechanisms to protect the micro hydroelectric power station from debris and sediment from the river;
• be protected from slush and icing for operation in winter;
• be able to change the water flow in the diversion canal quickly and in a controlled manner.

To ensure the supply of the required volume of water to the hydraulic unit, water backwater is required (raising the water level due to the complete or partial blocking of the riverbed (watercourse)). Backwater in the case of dam micro hydroelectric power plants is created by a dam (dam), when the channel is blocked by a dam and the required level and supply of water is reached.

In the case of diversion micro HPPs, such a backwater is created by constructing a barrier in the riverbed in front of the entrance to the diversion channel. Such support can be created:

• adjustable - due to the installation of gates-regulators (locks);
• unregulated - through the use of improvised materials (stones, concrete structures, etc.).

The figures below show two common examples of the design of water intakes, in which it is possible to regulate the backwater to ensure its intake into the diversion channel. In the first case (Fig. 40), the necessary backwater is provided and regulated by locks.

Fig.40. The design of the water intake with the use of gates-regulators (locks)

In the second case (Fig. 41), the necessary support is provided by wooden beams laid horizontally in the path of the water flow. The beams are held by channel structures. A change in water pressure (regulation) is provided by adding additional beams to raise the water level, or by removing them - to reduce the level of water being backed up.

Fig.41. The design of the water intake using wooden beams and channel

In other cases, it is possible to create an unregulated water backwater - by laying stones (barrage) or other materials (pieces of reinforced concrete, etc.) on the bottom of the river immediately after the entrance to the diversion channel. Figure 42 below shows, as an example, a drawing of a water intake facility on the Taldy-Suu River (Tyup district) for a micro hydroelectric power station with a capacity of 60 kW.

Fig.42. Drawing of a water intake facility on the Taldy-Suu River (Tyup district) for a micro hydroelectric power station with a capacity of 60 kW

The entrance to the diversion channel must be well reinforced from water erosion and made of reinforced concrete or rubble concrete. It must be equipped with a gate-regulator (gateway) to ensure a change in the volume of water taken into the diversion channel, as well as to completely shut off the water supplied to the hydroelectric unit for the period of repair or maintenance of the micro HPP (Fig. 43).

Fig. 43 Water intake lock of the diversion canal on the Taldy-Suu River (Tyup district) for a micro hydroelectric power station with a capacity of 60 kW

The entrance to the diversion channel should have a ledge (Fig. 44), as a trap for stones, gravel, sand and other sediments. However, the ledge cannot provide 100% sediment protection, this is the first barrier on their way. The design of hydraulic structures may provide for other devices to protect against sediments installed further than the intake structure. The ledge is made in the area of ​​the entrance to the diversion channel, in the form of a depression at the bottom. It must be periodically checked for fullness and requires regular cleaning.

Fig. 44 The classic version of the water intake structure (cross-sectional view of the structure)

derivation channel

The diversion channel is used to deliver water from the water intake facility to the penstock. It can be made in the form of an earth or concrete channel, or be built from concrete trays or hedgehogs - in the form of a plastic or metal pipeline, as is practiced in the Scandinavian countries.

The diversion channel can be of any length - from zero (if the pressure pipeline starts immediately from the water intake or dam) to several kilometers.

Most economically viable diversion channels are open earth channels. But they have a number of problems associated with high maintenance requirements; water loss; landslides caused by seeping water from unlined canal walls, the need to have a stable and relatively flat slope. For this, when constructing an earthen diversion canal, it is necessary to take into account the calculation of its slope within the values ​​of 0,002.0,003, that is, a change in height by 2-3 m for every 1000 m of the canal length. Increasing the slope can lead to subsequent erosion of the earthen walls of the canal, and reducing it can cause it to freeze in winter.

Diversion channels made of reinforced concrete (including trays and sections of high-speed currents), as well as metal or plastic, do not have the disadvantages inherent in earthen diversion channels - they are stronger and more durable, require less maintenance and repair. Such canals may have a steeper slope than earth canals and thus be less prone to freezing. To prevent freezing, diversion channels made of such materials can be additionally insulated (covered with slabs, insulating materials, deepened into the ground.

However, when designing, it must be borne in mind that a large slope of the diversion channel (and, accordingly, a high flow rate) has certain disadvantages.

Firstly, a more complex design of the pressure basin - water must enter it in compliance with a certain regime, as a rule - in a calm state, so as not to form breakers inside the pressure basin, and also not to destroy it over time. A large slope of the diversion channel, and, accordingly, a high flow rate, in general, can lead to the rapid destruction of hydraulic structures of micro hydroelectric power plants.

Secondly, a large slope reduces the pressure (height difference between the upstream and downstream). Accordingly, this will reduce the capacity of the micro hydroelectric power station. The head height is an important factor in the power, and most importantly, the cost of a micro hydroelectric power station. Low head equipment is much more expensive than high head equipment. It is also large in size and entails the construction of larger structures for its installation (support foundation, machine room, etc.).

The table below summarizes the main data on materials for the construction of a diversion canal, with their strengths and weaknesses.

A useful design for ensuring the operation of a micro hydroelectric power station is a sludge chute. The sludge discharge device prevents sludge, which is formed during the cold season, from entering the pressure basin and the turbine chamber. It is placed in the intake device in front of the diversion channel with a sufficiently short diversion channel and provided that the sludge is formed only in the river. With long diversion channels, there is a possibility of sludge formation in the channel itself. In this case, sludge-discharge devices are placed in front of the pressure basin.

The noise-discharging device in the form of a transverse tray is installed perpendicularly or at some angle to the direction of water flow in the diversion channel (Fig. 45).

Fig.45 An example of a noise discharge on a derivation channel

The bottom of the sludge tray is placed below the water horizon so that the sludge does not pass under it, but is discharged from the back wall into the sludge channel, which would divert the collected water with sludge into the river. The sludge release device is removed when there is no sludge.

pressure basin

The pressure basin of a micro hydroelectric power station is a structure for interfacing a diversion channel with a pressure pipeline, to create the necessary pressure and volume of water, as well as to clean the stream from litter, sediment and discharge excess water. It also ensures that the water regime necessary for the correct operation of the hydraulic unit is maintained.

The classic pressure basin design includes (Fig. 46):

• interface with the diversion channel (water entry into the pressure basin);
• overflow wall - for dumping excess water and floating debris;
• gates (locks) for regulating the water flow in the pressure pipeline and discharging water and bottom sediments;
• spillway - for water drainage;
• trash grate - to prevent debris and driftwood from entering the pressure pipeline.

Fig. 46 Project of a 60 kW micro HPP pressure basin on the Taldy-Suu River (Tyup district)

The pressure basin must be made of reinforced concrete. The size of the pressure basin is usually determined based on the equipment manufacturer's specification. It must have a minimum headroom in order to cope with rapidly changing turbine flow without excessively lowering the water level in the forebay. As a general rule, the required headroom volume margin corresponds to 30 seconds of turbine design flow.

Pressure pipeline

Pressure pipelines supply water from the pressure basin to the turbine chamber. They can be installed either on the surface of the earth or underground.

Above ground installation is the preferred option if the pipeline route is in rocky terrain where excavation of the trench would be too costly. Metal pressure pipelines are also preferably located above ground to facilitate maintenance and corrosion prevention work.

An underground pressure pipeline can have a number of advantages for the following reasons:

• no need for expansion joints;
• intermediate supports on which the pipeline is laid are not required;
• cushion materials (sand bedding) surrounding the pipeline can absorb shock loads.

The disadvantages of underground pipelines are additional costs, and that in steep sections the pad materials can be washed away, so it is necessary to make fences to contain the material.

The table below provides basic information on materials for pressure pipelines.

station building

The building of the micro hydro power plant is the place of installation of the hydroelectric unit and the control system of the micro hydro power plant. It also provides equipment protection from rain, snow and low temperatures.

There are many ways to build above ground, which must be done depending on local codes and regulations, material availability and climatic conditions. For mountain climate conditions, walls made of brick or masonry, or reinforced concrete blocks are usually suitable.

Transformers should be located either outside the station building or in a separate room.

The best option for building a foundation for a building and a supporting foundation for a hydraulic unit is reinforced concrete. With small sizes of equipment, it is allowed to build a foundation of rubble concrete.

The best option is to use the detailing drawing of the supporting foundation for its correct construction and compliance with the necessary specifications for fixing the equipment. This is usually provided by the equipment manufacturer or contracting organization. Figure 47 below shows a micro HPP building with a capacity of 60 kW on the Taldy-Suu River (Taldy-Suu village, Tyup district).

Fig. 47 Scheme of the building of a micro hydroelectric power station with a capacity of 60 kW on the Taldy-Suu River (Tyup district)

This drawing shows the main elements of the power plant building and the supporting foundation of the hydroelectric unit. This micro HPP has a radial-axial turbine with a vertical turbine shaft.

The following points should be considered when designing any station building:

• adequate ventilation to remove generator heat losses;
• a block for lifting the turbine, generator and gates during periodic repairs and maintenance;
• sufficient working space inside the building to repair equipment;
• entrance doors of sufficient size to bring in the largest pieces of equipment;
• a trench or trough for a pressure pipeline with drainage so that water leaks do not flood the station building;
• grounding in the foundation of the building, or grounding rods sunk into the ground at several points around the building.

Particular attention must be paid to the construction of a diversion tract for the correct diversion of water from the turbine into the river. The outlet tract must be reinforced so that the outgoing water does not erode both the tract itself and the places where the water flows into the river. It can be made of reinforced concrete. It is allowed to manufacture it from rubble concrete, subject to the relative low power of the micro hydroelectric power station.

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

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