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Principle And Structural Characteristics Of Water Flow Action Of Counter-Turbine Generator

Author: source: date: 2020-09-30 14:17:42

Principle and structural characteristics of water flow action of counter-turbine generator


The counter-turbine is a hydraulic machine that uses the pressure of the water flow to convert water energy into mechanical energy.


(1) Structure. The main structural components of the counter-turbine are the runner, the diversion chamber, the water guide mechanism and the draft tube.

1) Runner. A runner is a part of a water turbine that converts water flow energy into rotating mechanical energy. According to the different direction of water energy conversion, the structure of various counter-turbine runners is also different. The Francis turbine runner is composed of streamlined twisted blades, the crown and the lower ring and other main vertical components; the axial flow turbine runner is composed of the main components such as blades, runner body and drain cone: the structure of the diagonal flow turbine runner is more complex. The blade placement angle can be changed according to the working conditions, and is matched with the guide vane opening, the blade rotation center line is at an oblique angle (45° ~ 60°) with the turbine axis.


2) Diversion room. Its function is to make the water flow evenly flow into the water guiding mechanism, reduce energy loss, and improve the efficiency of the turbine. Large and medium-sized hydraulic turbines with a water head of more than 50m often use a circular cross-section metal volute, and those below 50m often use a trapezoidal cross-section concrete volute.


3) Water conducting agency. It is generally composed of a certain number of streamlined guide vanes and their rotating mechanisms arranged uniformly around the periphery of the runner. Its function is to guide the water flow to the runner evenly, and to change the flow rate of the turbine by adjusting the opening of the guide vane to adapt to the load requirements of the generator set. It also plays the role of sealing the water when it is fully closed.


4) Draft tube. There is still some unused energy left in the water flow at the runner outlet. The function of the tailpipe is to recover this part of energy and discharge the water downstream. The draft tube is divided into two types: straight tapered and curved. The former has a large energy coefficient and is generally suitable for small horizontal and cross-flow turbines; the hydraulic performance of the latter is not as good as straight cones, but the digging depth is small, and it is widely used in large and medium-sized impact turbines.


(2) Classification. Counterattack turbines are divided into Francis turbines, Diagonal turbines, Axial turbines and Tubular turbines according to the axial direction of the water flow through the runner.


1) Francis turbine. Francis type (radial axial flow or Francis type) turbine is a counterattack turbine with water flowing axially from the circumference of the runner to the flow direction. This type of turbine has a wide range of applicable heads (30-700m), simple structure, small volume and low cost. The largest Francis turbine that has been put into operation in my country is the turbine of Ertan Hydropower Plant, with a rated output power of 582MW and a maximum output power of 621 MW.


2) Axial flow turbine. Axial-flow turbine is a counter-turbine with water flowing in axially and flowing out axially. This type of turbine is divided into two types: fixed pulp type (screw type) and rotary paddle type (Kaplan type). The former blades are fixed and the latter blades can rotate. The flow capacity of axial flow turbines is greater than that of Francis turbines. The paddle-turbine turbine can change its position with the change of load, so it has high efficiency in a large load change range. The axial flow turbine's anti-cavitation performance and mechanical strength are inferior to the Francis turbine, and its structure is more complicated. At present, the applicable head of this turbine has reached more than 80m.


3) Tubular turbine. The water flow of this type of turbine is axially flowing from the axial flow runner, and there is no counter-rotating turbine that has any rotation before and after the runner. The head range is 3-20. . The fuselage has a small height, good water flow conditions, high efficiency, low civil engineering cost, low cost, no volute and curved draft tube, etc., and the lower the head, the more obvious the advantages.

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According to the connection and transmission mode of the generator, the tubular turbine is divided into two types: full-through type and semi-through type. The semi-through type is further divided into bulb type, shaft type and shaft extension type. There are inclined axis and horizontal axis. At present, the most widely used are the bulb flow type, shaft extension type and shaft type, which are mostly used for small units. In recent years, the shaft type is also used in large and medium-sized units.


The generator of the shaft through-flow unit is installed outside the water channel, and the generator is connected to the turbine with a long inclined shaft or horizontal shaft. This shaft-extended structure is simpler than the bulb type.


4) Diagonal flow turbine. The structure and size of diagonal flow (also called diagonal) turbines are between Francis and Axial flow. The main difference is that the centerline of the runner blades is at a certain angle from the centerline of the turbine. Due to the structural characteristics, the unit is not allowed to sink during operation, so the structure 2 is equipped with an axial displacement signal protection device to prevent accidents where the blades collide with the runner chamber. The head of the inclined flow turbine is 25~200m.


At present, the largest single-unit rated output power of oblique-drop turbines in the world is 215MW (former Soviet Union), and the highest utilization head is 136m (Japan).

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