Introduction to civil work construction for micro-hydropower systems

Although the hydraulic construction of micro-hydro power generation is small, its quality determines whether the micro-hydro generator set can be in the best working condition.

Diversion Canal
The diversion canal is responsible for the dual task of diverting water and forming the head for power generation. The main points of the construction of the diversion channel are as follows.
1) The channel should be chosen as far as possible to avoid areas with landslides, rock crumbling and sand flow.
2) The channel should be as short and straight as possible, avoiding sharp bends to reduce head loss.
3) channels should try to avoid passing through ditches, depressions, steep walls, to reduce the construction of hydraulic buildings.
4) channel slope drop according to the size of the flow and soil conditions, micro hydropower stations generally use 1/100 ~ 1/300.

Safe flow rate is based on the channel soil and masonry materials and water flow containing sand and mud, to determine the flow rate without flushing or siltation. General experience, the flow rate of soil canals using 0.5 ~ 0.8 m / s. When the average flow speed is less than 0.5m/s, the plants are easy to reproduce; when it is more than 0.8m/s, it is easy to scour the channel.

Pressure front pond
Pressure before the pool is the channel and pressure water pipe connection structure, before the pool structure as shown in Figure 4-1. Before the pool construction points are as follows.

Before the pool can be used brick or cement slurry stone, concrete can be cast as a whole. The front pool inside and outside the surface with cement smoothing leak-proof. If the front pool is built in the place where people store access, should build a guardrail or add a cover.

The volume of the front pool should not be less than 5 cubic meters, the volume as much as possible to expand the front pool to make it more effective in regulating the effectiveness of water. Pressure water pipe mouth submersion depth should be greater than 0.8 meters, otherwise it is easy to form a whirlpool, so that the air into the pipe, affecting the turbine power.

The cross-sectional area of the overflow mouth of the front pool should not be smaller than the water inlet to ensure that the incoming water from the canal can be fully discharged from the overflow mouth when the unit is shut down.

The sand discharge port is located at the bottom of the front pool, and the outside is connected with the overflow tank. The sediment washed out from the bottom of the pool is discharged to the downstream through the overflow tank.

In the front of the pool inlet should be set up barrage. Barrage is best set at an angle, and with the water surface into 70 ° ~ 80 ° angle, in order to remove the dirt along the channel. The flow velocity at the barricade should not be too large, should be controlled within 0.4 m / s.

Drainage ditch
Different turbines have different requirements for drainage ditch. The general requirement of the drainage ditch is to ensure smooth tailwater drainage so that the water can be discharged smoothly into the downstream river. The drainage ditch should be built at the same time with the foundation of the machine room, and the two should be connected as one, while not allowing the tailwater to impact the foundation of the machine room.

Diversion weir and water storage weir
The function of the diversion weir is to introduce river water into the water channel according to the amount needed for the generator set, as shown in Figure 4-2. The amount of water introduced is limited by the size of the water outlet connected to the canal. The function of the weir is to stop most or all of the water into the canal during the dry season, while the excess water is smoothly discharged through the diversion opening of the weir when there is a lot of water or when a flood comes.

In places where water resources are insufficient and the terrain is conducive to the construction of water storage weirs, water can be stored by building weirs, as shown in Figure 4-3. The volume of the water storage weir is usually within the range of 500 to 1500 cubic meters, which is stored during the day and sent at night to solve the problem of lighting electricity for local households at night.
Micro-hydroelectric power generation project’s diversion and storage weirs are mainly slurry block stone dams. Since mountain streams often have a high sediment content, weirs are best used to release water from the bottom culvert. The weir and storage weir can be combined into one, or built separately.