Types of hydroturbines of micro hydroelectric power plants. Encyclopedia of radio electronics and electrical engineering

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Propeller turbines (Kaplan turbine)

The propeller turbine has the highest speed among all types of turbines. This makes it possible to obtain a higher rotation speed at low flow rates. High turbine speeds, in turn, allow the use of faster, and therefore lighter and cheaper electric generators or reduce the cost of transmission devices (gearboxes or belt transmission systems). Therefore, propeller turbines are used at the lowest pressures, when the flow rates are low.

In appearance, the propeller turbine impeller looks like a fan (Fig. 20).

Fig.20. Propeller turbine with fixed blades

The blades in the turbine can be made both fixed and rotary (Fig. 21). In the first case, the blades are fixed at a selected angle corresponding to the operating pressure and the optimal load of the generator. Rotary blades are justified to be used in large turbines with significant pressure fluctuations and generator operation under variable load conditions. With the help of rotary blades, it is possible to maintain a constant speed of rotation of the impeller and the frequency of the generated voltage in the generators.

Fig.21. Kaplan turbine

Fig.21-1. Principle of operation

The propeller turbine has a guide vane (Fig. 22), which serves to feed the water flow at the right angle to the turbine blades to achieve maximum efficiency. The guide vane allows you to adjust the power of the turbine, and, in some cases, completely stop the access of water to the turbine wheel.

Fig.22. Turbine guide vanes

Propeller turbines are equipped with suction pipes. The suction pipe is a channel expanding in cross section for draining water from the turbine. With an increase in the cross section of the pipeline, the speed of water and its kinetic energy decrease, which makes it possible to reduce energy losses in the outgoing stream. In addition, the suction pipe allows the turbine to be located above the water level in the downstream.

Beef (fr. bief) is a part of the body of water adjacent to a hydraulic structure. A distinction is made between upstream (adjacent to the forebay) and downstream (adjacent to the discharge channel).

Suction pipes are either straight or curved, as shown in Fig. 23 and 24:

Fig.23. Hydraulic unit with direct suction

Fig.24. Hydraulic unit with curved suction pipe

Radial-axial turbines (Francis turbine)

Water enters the impeller of a radial-axial turbine from the outside of the wheel and moves along the radius towards the center of the turbine (Fig. 25). Having passed between the blades of a complex spatial curved shape, the water gives energy to the rotor, causing it to rotate.

Fig.25. Radial-axial (Francis turbine)

Fig.25-1. Radial-axial (Francis turbine), appearance

For a correct and uniform supply of water around the entire circumference of the impeller, it is surrounded by a spiral chamber (Fig. 26). A guide apparatus is placed between the spiral chamber and the wheel, consisting of blades that direct water to the turbine wheel at the desired angle. The guide vanes can be made rotatable to change the water flow and the best direction of the flow to the impeller blades (Fig. 27). This increases the efficiency of the turbine in off-design modes. The guide apparatus can be equipped with a manual adjustment system, or an automatic one.

Fig.26. Scheme of the volute and guide vanes of the Francis turbine

Fig.27. Francis turbine with manually adjustable guide vane

In radial-axial turbines, there is a risk of water hammer in the pressure pipe. In the event of a generator failure or a sharp drop in load, the guide vanes reduce the water flow, and a water hammer occurs in the pressure pipeline, which can lead to a rupture of the pipeline. To prevent accidents, radial-axial turbines are equipped with a safety idle outlet that discharges water from the spiral chamber into the downstream during pressure surges.

For high-pressure radial-axial turbines, it is important to reduce the possible leakage of water past the impeller blades. This is achieved by high precision manufacturing of mating parts and special seals that reduce pressure losses.

After passing through the impeller, the water enters the suction pipe, which has a conical shape. Passing through the suction pipe, the water increases its cross section and slows down, which leads to a decrease in the kinetic energy of the uselessly leaving with the waste water. In addition, the suction pipe makes it possible to locate the hydroelectric units much higher than the downstream of the water, which is convenient for the construction of a hydroelectric power station building.

For the production of turbines, special highly wear-resistant steel grades are used to ensure long-term and reliable operation of turbines.

Pelton turbines (Pelton turbines)

This type of turbine is used for high pressures. The pressure pipeline enters the building of the hydroelectric power plant and ends with a nozzle directing the jet to the turbine impeller. A jet of water emerging from the nozzle rolls over the concave surface of the bucket and changes the direction of its movement to the opposite (Fig. 28).

Fig.28. Ladle Diagram (Pelton Pelton Turbine)

Fig.28-1. Impeller (Pelton bucket turbine)

The maximum efficiency will be in the case when the jet reflected from the bucket has zero speed with respect to the body. This is achieved, as the analysis shows, at a circumferential speed of the ladle equal to half the speed of the jet.

The buckets in the turbine are made paired and the jet is fed to the junction of the buckets to compensate for axial forces on the rotor bearings. The turbine nozzle serves to regulate the amount of incoming water. The needle moving inside the nozzle changes the cross section of the channel and the flow rate of water entering the turbine wheel (Fig. 29).

Fig.29. Needle Valve Nozzle Schematic (Pelton Pelton Turbine)

In addition to the nozzle, a deflector is used to adjust the parameters of the turbine, which is an obstacle located between the nozzle and the bucket, which deflects the jet and reduces the force of the jet on the rotor of the hydraulic unit. The deflector allows you to avoid hydraulic shocks when adjusting the turbine. When regulating the jet only with a needle, in the event of a sharp drop in the electrical load in the network, the needle blocks the water outlet, which causes a water hammer in the pipeline, and the possibility of damage to it. Waste water flows downstream. Therefore, to reduce pressure losses, the nozzle and turbine should be located as low as possible to the level of the flow. The turbine housing is used to protect against splashes of the hydroelectric plant room and is made large so that water reflected from the housing does not fall back onto the rotor and does not reduce the efficiency of the installation.

In bucket turbines, several nozzles are often installed spaced around the circumference of the impeller, which reduces the load on the rotation bearings (Fig. 30).

Modern hydraulic turbine construction is developing taking into account the following main trends:

• increase efficiency and reliability in operation;
• increasing the speed of hydraulic turbines in order to provide the required design power with smaller dimensions and weights of hydroelectric units, which ensures a reduction in the cost of power equipment and the HPP building;
• improving the energy characteristics of hydraulic turbines and increasing the average operational efficiency of units when operating at off-design loads and pressure;
• reduction of pressure pulsations in the flow path (especially behind the impeller of a radial-axial hydraulic turbine) and the accompanying vibrations of the unit;
• hydraulic units;
• the use of powerful hydroelectric units at HPPs makes it possible to reduce their number, increase efficiency and reduce the cost of power equipment and buildings;
• further growth of unit capacities.

Fig.30. Pelton turbine with two nozzles

Transfer devices

Transmission devices are needed to transfer rotational energy from the turbine to the generator. Some designs of micro hydroelectric power plants provide for direct transmission of energy through a shaft (the impeller and the generator rotor are on the same shaft). Other transmission systems (belt or gear) can both change the gear ratio of rotation of the impeller to the generator rotor, and transmit it without changes.

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

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