| When the lower reaches of the hydropower plant have a long pressure tailrace tunnel, in order to prevent the tail water system producing high water hammer pressure in the transient process, and to protect the unit from the tail pipe reverse water hammer caused by failure, we need to set up tailrace surge chamber to reduce the water hammer pressure.In this paper, establishing the mathematical model and boundary conditions analysis of the diversion system with pressure of hydraulic transition process, combining the pressure fluctuation of water hammer with quality fluctuation of chamber to calculate, studying and comparing the two kinds of different layout of the surge chamber in hydraulic transition process . The main conclusions are as follows:(1) In three different closed ways of guide vane, fast followed by slow of the two segment closing law can effectively reduce the maximum pressure at the end of volute and the maximum rising ratio of rotating speed, when the turbine is in the transition process of load rejection ,selecting appropriate closing time and breakpoint opening can improve the characteristics and control parameters economically and effectively.(2)Selecting the reasonable impedance hole diameter can accelerate the speed of water hammer wave attenuation, make the unit operate more safely and stably ,at the same time, it can reduce the pressure chamber excavation area, reduce the amount of excavation, reduce project cost. When the impedance hole diameter is same , the different arrangements of surge chamber also have a great influence on the volute end pressure, rotating speed, surge water level and other parameters.Therefore, we should analysis the problem comprehensively and comparatively before arranging the position of surge chamber.(3)Analysing the surge chamber position effect on the minimum pressure in draft tube, not the tailrace surge chamber is closer to the plant is more favorable to the unit, there is an optimal critical position, when exceeding the critical position and closing to the plant, there is no influence for the minimum pressure in draft tube.Thus,increasing the distance between the plant and the tailrace surge chamber can make the surrounding rock of underground caves more stably , at the same time, increasing the area of surge chamber can significantly improve the minimum pressure in draft tube.(4)The pressure of tailrace channel roughness on different parameters of the transition process has a certain influence. When increasing the tailrace channel roughness,the maximum pressure at the end of the volute and the rise rate of the maximum speed of the unit decreasing,the minimum pressure in draft tube increasing, the amplitude of surge water level decreasing,the hydraulic transition process of hydropower station is more secure. However, increasing the roughness, the anti-seepage effect of the tail channel becomes worse, head loss increasing, the flow pattern is getting worse. So combined with the actual project, the final roughness of the tailrace tunnel is 0.014. |
