The hydroelectric generating set includes turbines, generators and their associated turbine governors, hydraulic devices, excitation devices and power station control equipment.
According to the working water head level, the hydraulic generator group can be divided into low head, medium head and high head hydraulic generators. Due to its low water head, a low-head hydraulic generator must require a large water flow to obtain a certain power generation power. A typical machine has an axial-flow hydraulic generator; Compared with low-head hydroelectric generators, the required water flow is small, and the typical machine is a bucket type hydroelectric generator.
The hydroelectric generating set can also be divided into vertical type and horizontal type according to the installation method. The vertical hydraulic generator set is installed upright, and the rotating shaft is perpendicular to the ground. Since the generator is on the upper part and the turbine is on the lower part, it is beneficial to the generator to be waterproof and moisture-proof. Generally, large and medium-sized units with low and medium speed are mostly used vertically. The horizontal hydraulic generator set is installed horizontally, and the rotating shaft is parallel to the ground. Horizontal hydro-generators are suitable for small and medium-sized, tubular and impact turbines.
Prompt: The demarcation boundaries of low, medium and high water heads of hydroelectric generators of different power sizes are different. The low head of small hydroelectric generators may refer to less than 6m, while the low head of large hydroelectric generators generally refers to Below 30m.
The turbine in the generator set is a hydraulic prime mover that converts water energy into mechanical energy and provides the motive power for the generator.
According to the action of water flow on the runner of the turbine, the turbine can be divided into two categories: the impact turbine and the impact turbine. The energy conversion of the runner of the impact turbine is carried out in a pressurized pipe flow; the energy conversion of the runner of the impact turbine is carried out in an unpressurized atmosphere.
Various types of turbines have many different forms due to their different structures. Impact turbines include Francis flow, axial flow (axial flow rotary paddle type, axial flow fixed paddle type), oblique flow and tubular flow (through flow rotary paddle type, tubular fixed paddle type), etc.; impact turbines have water Bucket type, oblique type and double-click type, etc. The working principles and characteristics of various types of turbines will be introduced below.
- Counterattack turbine
The impact turbine is the most widely used in hydropower stations and is suitable for hydropower stations with various heads and flows. Its application range is water head H=2~300m, output P=4~10000kW.
The impact turbine mainly uses the pressure energy of the water flow (a small part is the water flow energy) to do work. When the water flow passes through the runner blades, the water flow changes the pressure and flow rate due to the action of the blades, thus producing a reaction force on the blades, forming a rotating torque, and making the runner rotate.
According to the direction of the water flow through the runner, the impact turbine can be divided into axial flow, Francis flow, oblique flow and tubular flow. Axial turbines and Francis turbines are basically the same in structure, and the main difference between the two is the runner. The tubular turbine is the same as the runner of the axial turbine.
1) Axial turbine
Axial turbines are characterized by the fact that when the water flows through the runner, it is always in the direction of the axis.
The water flow of the axial-flow turbine has turned a 90° angle before entering the runner. The water flow enters the runner along the axis of the main shaft and flows out of the runner along the axis of the main shaft. The water flow in the runner performs both rotational motion and axial motion, and there is no radial motion, so it is called “axial flow. This type of turbine is suitable for hydropower stations with a head of 3~80m, and is a low-head, high-flow model.
2) Francis turbine
The characteristic of Francis turbine is that the water flow enters the runner radially first, and then flows out of the runner approximately axially.
The runners of Francis turbines look complex, and are shaped so that all the water flow through the blades pushes the runners into rotation. When the water flow enters the runner, it pushes the runner when it passes through the blades in the direction of the axial core, and also pushes the runner when it passes through the blades downward.
The water flow of the Francis turbine enters the radial direction of the main shaft at the front of the runner, turns oblique in the runner, and finally flows out of the runner along the axis of the main shaft, as shown in Figure 4.7. While the water flow is rotating in the runner, it also performs radial and axial movements, so it is called “mixed flow”.
This type of turbine is suitable for hydropower stations with a head of 30~800m. It is a medium head and medium flow type. At the same time, it runs stably and has high efficiency. At present, the highest efficiency of the runner has reached 94%, which is the most widely used turbine.
3) Diagonal flow turbine
For the oblique flow turbine, the water flow in the runner is the same as that of the Francis turbine, but its runner blades are the same as those of the axial-flow rotary paddle turbine, as shown in Figure 1.
This type of turbine absorbs the advantages of Francis and Axial Rotary paddle turbines, and can adapt to a large water head range by adjusting the blade angle. The structure and process of the blade rotating mechanism of the oblique flow turbine are relatively complex, so the cost is high, and it is rarely used in China after the 1960s.
4) Tubular turbine
The feature of the tubular turbine is that the water flow is axial from the inlet to the draft tube outlet.
The runner structure of the tubular turbine and the water movement in the runner are exactly the same as those of the axial turbine. Different from the axial flow turbine, the water flow of the tubular turbine is almost always parallel to the main axis from entering the turbine to exiting the turbine, hence the name “tubular flow”.
Since the water flow into and out of the turbine is almost smooth, the over-current capacity of the turbine is very large, and electricity can be generated as long as there is a water level difference of 0.3m. This type of turbine is suitable for large-flow hydropower stations below 30m head, especially tidal power stations, which are ultra-low head and ultra-large flow models.
Tubular turbines are divided into four types according to their structural forms: shaft-extension tubular, bulb tubular, shaft tubular and full tubular. Among them, bulb tubular turbine has a reasonable structure and high efficiency, so it is widely used.
- Impact turbine
The impact turbine uses the kinetic energy of the water flow to push the turbine runner to rotate to do work. It does not need draft tubes, volutes and complicated water guiding mechanisms, so its structure is simpler than that of impact turbines, and it is easy to maintain and manage.
The water flow in the impact turbine impinges on the runner in the form of jet, so that the runner outputs mechanical torque. According to the way the jet impinges on the runner, the impingement turbine is divided into bucket type, oblique flow type (or oblique stroke type) and double-click type.
The bucket turbine is currently the most widely used impact turbine, which is suitable for power stations with high head and small water volume. The oblique type and double-click type turbines are simple in structure and easy to manufacture, but their efficiency is low, and they are mostly used in small rural power stations with small output.
1) Water bucket turbine
The bucket turbine is currently the most widely used impingement turbine, which is customarily called the impingement turbine. The water flow of this type of turbine is formed by the nozzle to form a high-speed moving jet, and the jet impacts the bucket blades of the runner along the tangential direction of the rotating plane of the runner, so it is also called a shear-impact turbine. The bucket of the bucket turbine consists of two scoop-shaped bodies juxtaposed.
This type of turbine is suitable for hydropower stations with a head of 100~1700m, and is a type of high head and small flow. The water head range of the small bucket turbine is 100~300m, and the output is below 2000kW. Large bucket turbines can be used in hydropower stations with a head of more than 700m.
2) Inclined type turbine
The main working parts of the oblique type turbine are basically the same as those of the bucket type turbine, except that the working jet and the runner inlet plane are at a certain angle a, and the jet is directed obliquely to the runner, so it is called the oblique type turbine. The oblique type turbine is suitable for smaller turbines, mainly used in places with high water drop, such as waterfalls, mountain streams, mountain streams, etc. The water head is 20~300m, and the power is below 500kW.
3) Double-click turbine
The application of the double-click turbine has a lower water head and does not have the nozzles in the bucket and oblique turbines. Instead, a nozzle with a rectangular section equal to the width of the runner is connected to the end of the pressure pipe. The water flow formed by the double-click turbine is relatively small. After the water flows out of the nozzle, it first enters the runner from the top of the outer cylindrical surface of the runner and flows through the blades, converting 70% to 80% of the water energy into mechanical energy, and then from the runner. The inner cavity falls, bypasses the main shaft and enters the runner centrifugally from the inner cylindrical surface of the runner and flows through the blades for the second time, converting the remaining 20%~30% of the water energy into mechanical energy, and finally the water flow centrifugally leaves the rotor from the outer edge of the blade. wheel. The so-called “double-tap” means that the water flows over the runner blades twice.
The double-click turbine has a simple structure but the lowest efficiency, and is suitable for small rural hydropower stations with a head of 5~100m.
- Reversible turbine
Reversible turbine is a new type of turbine, which is mostly used in pumped storage power stations and tidal power stations. The reversible turbine in the pumped-storage power station can operate as a water pump during forward rotation to pump water for energy storage; during reverse rotation, it can operate as a turbine to discharge water to generate electricity. The reversible turbines used in tidal power plants can be used for pumping water storage in both forward and reverse rotations, and can also be used as turbines to discharge water to generate electricity. There are four types of reversible turbines: reversible Francis flow, reversible oblique flow, reversible axial flow and reversible tubular flow.
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