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 choice of location and layout of micro HPPs are determined by natural conditions, capabilities and desires of the future user. All these issues are complex and include both hydrological parameters and electrical, construction and economic issues. Should be considered main issues of construction of micro hydroelectric power plants.

Power lines

It is preferable to build a micro hydroelectric power station closer to housing, to the consumer, since with an increase in the distance and the corresponding length of power lines, both the costs of building, installing and maintaining these lines increase, as well as the loss of electricity due to resistance in power lines (TL).

 Electrical resistance is a physical quantity (expressed in ohms) that characterizes the resistance of a conductor to electric current (power line wires). This value varies depending on the material, cross section and length of the conductor.

Figure 34 shows the losses on the example of a micro hydro power plant with a capacity of 10 kW. The calculations shown in the figure compare the losses in a power transmission line with a length of 3 km and 200 meters (wire material - aluminum with a cross section of 25 mm).

Fig.34. Calculation of electricity losses depending on the length of power lines

As you can see, the voltage drop in the power transmission line with a length of 3 km was 68%, while in the power transmission line of 200 meters - only 5%.

At sufficiently large hydroelectric power plants (or powerful small hydroelectric power plants), this problem is solved by transmitting electricity to a substation, where its voltage is increased to hundreds of kilovolts, which makes it possible to transmit large power through power lines with a minimum wire cross section and with minimal losses. Technically, a system of transformers (to increase the voltage followed by a decrease in voltage) can also be supplied for micro HPPs, but this will increase the overall cost of micro HPPs.

The second factor in reducing the voltage / power indicators reaching the consumer is the material and cross-section of the wires of the power transmission line.

Why is it necessary to calculate wires and cables for long-term permissible current? First of all, calculations are performed for a safe and reliable power supply. Another important factor is the economic part. It would be easy to take a thick copper wire and, without counting anything, be sure that the electric current will pass through such a wire without loss. But the cost of such power lines will not be economically justified.

It is understood that with the same current in the power line and with an increase in voltage, more power can be transmitted. This means that with a constant cross-section of the wire of a power transmission line, it is possible to transmit large powers over long distances.

Therefore, for a technically and economically efficient micro hydroelectric power station, it is necessary to choose a place for its construction as close as possible to consumers and use appropriate materials for power transmission lines.

Assessment of hydrological parameters

The potential capacity of a micro HPP is calculated on the basis of two main indicators:

• water pressure in meters;
• water consumption in liters (or cubic meters) per second.

These indicators are used in the following formula for calculating the productive capacity of the selected area:

,

where: P = electrical power, kW; Q = flow rate, m3/s; H = head value, m; g = gravitational acceleration (9.81 m/s2); η = overall efficiency (use 70%).

As you can see, for the calculation it is necessary to enter the values ​​\uXNUMXb\uXNUMXbof the pressure and flow of water into the formula. To obtain this data, there are many ways suitable for calculating power - simple and complex, accurate and approximate.

The values ​​of pressure and water flow are the main indicators for choosing a site for the construction of a hydroelectric power station. In practice, there are places that are attractive for the construction of micro hydroelectric power plants, where it is quite easy to make a preliminary assessment of the head and flow. However, there are also often places where the parameters of the watercourse are not so clearly visible. This may be hindered by a small slope of the watercourse or an unorganized flow of water (when a river or stream consists of several channels or many inflows and outflows). In order not to make detailed measurements of pressure and water flow in different places every time, it is advisable to make a preliminary assessment in several places where the construction of a micro hydroelectric power station is visually feasible. This is necessary to select the best location for already detailed surveys.

For this, different methods are used. For example, you can use:

Cartographic data, which indicates elevations on the ground. Such maps are available from geologists, local Gosregisters, LSG or authorities responsible for irrigation. Such maps indicate all significant changes in elevation on the ground and water edges (river banks). With their help, you can preliminarily estimate the height difference and, accordingly, the potential pressure. It is also possible to approximately estimate the required length of the diversion channel (in the case of the diversion type of micro HPP).

• Leveling on the ground.
• Estimation of terrain heights and water lines using a GPS device, both special and available in some models of mobile phones.
• Estimation of average long-term water discharges based on the data of gauging stations.
• Data on water consumption from authorities responsible for irrigation.

This assessment will allow you to weed out less attractive places and start more detailed surveys in one or two places.

Water pressure gauge

For the construction of a sufficiently powerful micro hydroelectric power station (for example, more than 10 kW), it is preferable to conduct surveys with the help of specialists and their equipment. If this is not possible, or if it is planned to build a small micro hydroelectric power station, then you can conduct your own research using relatively simple means.

Fig.35. Determination of pressure using a hose with water

This method (Fig. 35) uses a transparent tube (for example, an irrigation hose) filled with water and the principle of communicating vessels. The water level at one end of the tube should be at the top mark; in this case, it is necessary to measure the distance from the water level at the other end of the tube to the ground (lower mark). At the next measurement, the level of the upper mark should be where the lower mark was at the previous measurement. The sum of these heights will give the total height between upstream and downstream (i.e. head).

The same principle is used when measuring pressure using a building level and a measuring bar (Fig. 36).

Fig.36. Determination of pressure using the building level

It is necessary that the board be located strictly horizontally (this is ensured using the building level) and the pressure is measured according to the same principle as indicated in the example with a tube.

Water flow measurement

Water consumption in mountain rivers and streams of Kyrgyzstan is observed:

• the largest - in June ... August;
• the smallest - in January ... March.

The maximum flow is usually 3 to 5 times the minimum flow. Therefore, when making an assessment, it is necessary to take as a basis the period of minimum water flow. As a rule, water consumption is minimal in the winter season, when the most electricity is required. The diagram below (Fig. 37) illustrates this relationship on the example of the Taldy-Suu River and the Taldy-Suu village (Tyup district).

Fig.37. Ratio of water consumption in the Taldy-Suu River and electricity consumption in the village of Taldy-Suu

As in the case of assessing the water pressure, two approaches can be used to assess the flow - with the help of specialists and their equipment, or independently, using improvised means (Fig. 38).

Method a) is more intended for small streams (stream, ditches) and uses domestic containers (bucket, barrel). It is necessary to detect the time of filling the container (the exact volume of which is known) and determine the flow of water.

Fig.38. Measurement of water flow using: a) buckets; b) float.

For large volumes, it is advisable to use method b). To measure the flow of water in this way, it is necessary to choose a place on the river bed, 5-10 m long, the most even in depth and width, and with a calm current. It is necessary to measure the depth and width of the flow in the area in several places and determine the average value. The second step is to determine the flow rate. To do this, a float is thrown at the beginning of the selected section (any light floating object, for example, paper, foam, etc.) and the time it takes for it to swim through this section of the river is measured.

The water consumption indicator is determined by the formula:

,

where: Q - water consumption, m3/s; h - flow depth, meters; b - flow width, meters; v - flow velocity, meters per second; f is the flow factor.

For this formula, it is necessary to apply the flow coefficient indicator (f = 0,5 ... 0,8). The rougher the coast, the rockier the bottom, the shallow depth and the greater the width of the channel, the smaller the value of f must be used in the formula.

Example:

• flow depth h is 0,4 m;
• flow width b - 1,0 m;
• flow velocity v - 0,5 m/s;
• flux factor f is taken as 0,6

Water consumption (Q) will be equal to: Q \u0,4d 1 x0,5 x 0,6 x 0,12 \u3d XNUMX mXNUMX / s.

Electricity needs assessment

A correct assessment of electricity needs is very important in order to determine whether your micro hydro power plant will be sufficient to meet your electricity needs.

First of all, in order to determine the volume of electricity consumption, it is necessary to take into account in which system it will be used - in public electric networks or in its own consumption network.

When transferred to the central system, any power produced by the micro HPP will go to the public network and, in this case, there is no need to calculate the ratio of consumption and production of electricity.

In the case of the operation of a micro hydroelectric power station in its own network, it is necessary to carry out calculations for the consumption and production of electricity. This is necessary to eliminate both the underproduction of electricity and its overproduction. If the underproduction can be compensated by the parallel consumption of electricity from public consumption networks (RES), then the construction of more than necessary capacity will lead to an unjustified increase in the cost of building a micro hydroelectric power station. In addition, as described in the "Micro HPP control system" section, excess electricity must be consumed by the ballast load (for example, heating elements for heating water) in order to ensure the normal operation of the hydroelectric unit. This also leads to an increase in the cost of construction, since the installation of a ballast load requires additional work and materials.

The potential capacity of micro hydroelectric power plants (electricity generation) is calculated taking into account the already known power calculation formula

As for electricity consumption, each device has its own indicator of electric power consumption.

For example, you can use the data in the table below for calculations. This table can be supplemented with data on the consumption of other electrical appliances.

At the same time, if it is envisaged that electricity will be used by a large number of consumers, then it is very difficult to determine how much power and at what time will be consumed. In this case, it is necessary to coordinate the mechanism of consumption with consumers. An example during peak hours (in the morning and evening), consumers should turn off (or not turn on) some electrical appliances, such as: irons, vacuum cleaners, heaters, electric stoves, etc.

Particular attention should be paid to electric motors and household electrical mechanisms based on electric motors (circular saw, sewing machines, pumps, compressors, etc.). When starting the electric motor, the starting current may increase by 3-5 times compared to the rated power, which is indicated on the electric motor. Simultaneous switching on of several electric motors can lead to the fact that for a short period of time the load on the SHPP will increase, beyond the allowable one, which may adversely affect its operation.

Information about the engine is indicated in its passport (in the documentation and on a metal plate attached to the body). Nominal values ​​are given here, i.e. those for which the engine is designed in its normal operation at the maximum permissible load.

For example, the plate says: P = 1,1 kW; U = 220 V; I = 4,3 A; f = 50 Hz; = 2810 rpm; Efficiency = 77,5%; cos f = 0,87. It means:

• P = 1,1 kW rated useful power on the motor shaft is 1,1 kW, or 1100 W
• U = 220 V line voltage is 220 V
• I = 4,3 A line current is 4,3 A
• f = 50 Hz mains frequency must be 50 Hz
• n = 2810 rpm rated rotation speed, i.e. motor speed at rated load is 2810 rpm
• Efficiency = 77,5% nominal efficiency (the ratio of useful shaft power to the consumed power of electricity received from the network, paid by the meter) is 77,5%
• cos f = 0,87 The power factor (also called "cos phi") is 0,87. The power factor is the ratio of the active power of electricity, i.e. one that can be converted into another form, in this case - into a mechanical one, to the full power of electricity.

Thus, taking into account the indicated coefficients, the consumption of electric power by the electric motor during operation will be about 1,5 kW.

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

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