Hydraulic turbines can be divided into impact turbines and impact turbines according to their working principles. The runner of the impact turbine is rotated by the impact of the water flow. The pressure of the water flow during the work is unchanged, mainly due to the conversion of kinetic energy. The runner of the impact turbine is rotated by the reaction force of the water in the water. Both energy and kinetic energy change, but mainly the conversion of pressure energy. The following China Francis Turbine Supplier will introduce you in detail.
Percussion turbines can be divided into two types according to the direction of the water flow: cut-type (also known as bucket type) and oblique type. The structure of the oblique impact turbine is basically the same as that of the bucket turbine, except that the jet direction has an inclination and is only used for small units.
Impact turbines can be divided into mixed flow, axial flow, diagonal flow and cross flow. Francis turbine is the most widely used turbine in the world. It was invented by American engineer Francis in 1849, so it is also called Francis Turbine. Compared with the axial-flow propeller type, its structure is simpler, the operation is stable, and the highest efficiency is higher than the axial-flow type. However, when the head and load change are large, the average efficiency is lower than that of the axial-flow propeller type. Some of the highest efficiency has exceeded 95%. Mixed-flow turbines have a wide range of heads, ranging from 5 to 700 meters, but the most widely used are 40 to 300 meters.
Mixed flow runners are generally made of low-carbon steel or low-alloy steel castings or cast-welded structures. In order to improve the anti-cavitation and anti-sand wear performance, stainless steel can be deposited on cavitation-prone parts, or stainless steel blades, and sometimes the entire runner can be stainless steel. The use of a cast-welded structure can reduce costs, make the runner size more accurate, and the runner surface smoother, which is conducive to improving the efficiency of the turbine. It is also possible to use different materials to make the blades, upper crown and lower ring.
In mixed-flow turbines, the water flows radially into the water guiding mechanism and flows out of the runner axially; in axial-flow turbines, the water flows radially into the guide vanes and axially enters and leaves the runner; in diagonal flow turbines, the water flows Radially enter the guide vane and flow into the runner in a direction inclined to the main shaft, or flow into the guide vane and runner in a direction inclined to the main shaft; in a cross flow turbine, water flows into the guide vane in the axial direction And runner. Axial flow, cross flow and diagonal flow turbines can be further divided into fixed and rotary paddles according to their structure. Fixed paddle type runner blades are fixed; paddle type runner blades can be rotated around the blade axis during operation to adapt to changes in head and load. Axial flow turbines are suitable for power stations with lower heads. At the same head, its specific revolution is higher than that of the mixed flow turbine.
The blades of the axial-flow fixed-paddle turbine are fixed on the runner body. The general installation height is 3-50m. The blade placement angle cannot be changed during operation, the structure is simple, and the efficiency is low. It is suitable for power stations with small load changes or by adjusting the number of generating units to adapt to load changes.
Axial-flow propeller turbine was invented by Austrian engineer Kaplan in 1920, so it is also called Kaplan Turbine. The general installation height is 3-80m. The runner blade is generally operated by an oil pressure relay installed in the runner body, which can be rotated according to the change in water head and load to maintain the optimal cooperation between the movable guide blade angle and the blade angle, thereby improving the average efficiency. The highest efficiency of hydraulic turbines has exceeded 94%.