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June 15, 2020
Water turbines, as the machinery that converts the energy of water flow into mechanical energy, can be traced back to 100 BC. The prototype is a water wheel, which is often used to irrigate farmland and process grain. With the changes of the times, science and technology are changing with each passing day, and hydraulic turbines are now mainly installed in hydropower stations and used to drive generators to generate electricity. The higher the water flow and head, the greater the power transmission. How to adjust the speed of the turbine?
In small hydropower plants, the restrictions on the frequency change of the alternating current are generally not strict. The rotation speed of some commonly used processing machinery such as rice mills and mills can also have a large range of change. , And most are manual operations. The speed of the turbine can be adjusted in different ways. The simplest and most effective way is to change the flow through the turbine when the load changes, so that the output of the turbine can always be balanced with the load to maintain a fixed speed. In small-sized counter-attack turbines, this type of speed regulating equipment mainly has the following types.
The first is the movable guide vane type. This type of speed regulation equipment relies on changing the opening of the guide vane to adjust the flow rate to achieve the purpose of speed regulation. The governor shaft is connected to the governor ring of the hydraulic turbine through a push-pull rod to turn the handwheel, so that the governor shaft drives the governor ring to rotate, and all guide vanes rotate at an equal angle to change the opening degree, so the flow into the turbine changes accordingly. When all the guide vanes are connected end to end, the water flow is cut off and the turbine stops working. For open-type horizontal-axis turbines with relatively small output, the opening of the guide vane can be adjusted by turning the speed control ring directly by hand.
The second type is the cylinder gate (drum gate) type. In the hydraulic turbine with fixed guide vane, the cross section of the water guide mechanism is changed by moving the position of the cylindrical gate at the periphery of the guide vane to achieve the purpose of adjusting the flow rate. There are three lifting points on the cylinder gate. After the hoisting rope passes through the three pulleys, they are combined into one and connected to the winch. When the sluice gate is rotated to raise the sluice gate, the cross section of the water guide mechanism increases and the flow increases; when the sluice gate falls, the flow rate decreases; when the sluice gate covers all the guide vanes, the water guide mechanism closes and the turbine stops working . The speed control of the sluice gate is simple and can be produced on site, so it is used more in small hydropower stations. However, when the gate is partially opened, the water flow is not good, the efficiency of the turbine will be reduced, and it may not be close enough when closed. Therefore, the gate closed by its own weight should have sufficient weight, generally more than 10 kg more than the buoyancy of water.
The third is the single guide vane type. The single guide vane type speed regulating device is installed at the inlet of the volute with a rotatable tongue guide vane, and the flow can be adjusted by changing the position of the guide vane. This type of speed control equipment has a simple structure and low cost, and is mostly used in small enclosed hydraulic turbines. In order to further improve the performance, the single guide vane tongue plate can be properly lengthened, and the position of the rotating shaft is moved forward.
The fourth is the speed regulation of the intake gate. When the water turbine does not have a water guide mechanism to adjust the flow rate, and the cylinder gate cannot be installed, the water inlet gate can be used to adjust the speed. There are four commonly used gates. The first one is the flat gate and the beam gate. This kind of gate speed control is not ideal, time-consuming and labor-intensive, and it is not easy to control. When it is partially opened, it is easy to form a jet. The inlet of the turbine is often not fully submerged. The water flow is turbulent and contains air, which is unfavorable for the operation of the turbine. Therefore, it is only used as an auxiliary speed control device. The second is the arc gate. It is relatively labor-saving and can be manipulated in the plant by ropes and pulleys. It is flexible and convenient, but it is also easy to form a jet when partly opened. The third is the blink gate. It consists of movable gate and fixed gate. It is fully open when overlapped and fully closed when staggered. The stroke from full open to fully closed is small, the duration is short, and the speed adjustment is relatively flexible. The fourth is the butterfly gate. It is similar to the single guide vane and is generally installed in front of the volute.