Analysis And Study On Transition Process Of Tail Water System Of Large Capacity Unit In High Altitude Area

In recent years,with the rapid development of our country’s hydropower industry,there have emerged many large-scale underground hydropower projects with high altitudes,large capacity of machine units,and long tail water systems.These engineering characteristics have made the hydraulic transition process of tail water systems particularly problematic,but this process is a key factor to ensure the safe and stable operation of hydropower stations.Therefore,for this kind of hydropower project,it is very necessary to conduct a comprehensive and in-depth study to the hydraulic transition process.Based on the previous research results,this paper uses the method characteristics to analyze the transition process of the tail water systems which with large-capacity unit in high altitude areas,and then we obtain the following research results:(1)Through the calculation of regulating guarantee for machine units,we optimized the wicket closure rule and deeply studied the mutual influence rule between the wicket closing process and the pressure distribution of the tailrace system,the pressure difference of the resistance plate and the turbine generator inertia,and other issues.Then we concluded a reasonable wicket closure rule for effectively control the inlet pressure of the draft tube to meet the requirements of the large-capacity unit power station in high-altitude areas.(2)Under large fluctuation transaction period,the impact of tailrace tunnel size,surge chamber type,impedance hole size,etc.on the transition process of large fluctuations is mainly studied,and it is concluded that:the influence of different structural types of surge chambers on the minimum pressure of the draft tube inlet were different,however,the reasonable use of impedance surge chamber can effectively control the minimum pressure of the draft tube inlet in high-altitude power station,which can meet the special requirements of the "Surge Chamber Design Code".Besides,the change of tailrace tunnel length has a greater impact on the inlet pressure of the draft tube.high-altitude power stations must effectively control the length of the tailrace tunnel.(3)Under small fluctuation period,the increase in the size of the impedance hole slows the attenuation of surge water level fluctuations in the surge chamber,and the adjustment quality of large-capacity unit deteriorates;the increase in tailrace tunnel length increases the surge water level in the surge tank and prolongs the fluctuation period,the regulation quality of the large-capacity generators becomes worse;increasing the section area of the surge chamber can improve the regulation quality of the unit.(4)Under hydraulic interference conditions,increasing the size of the impedance hole is detrimental to the stable output swing of the large-capacity disturbed unit and the stable surge water level fluctuation of the surge tank;increasing the tailrace tunnel length slows the attenuation of the surge tank water level fluctuation and causes adverse effects to the stability of the system;increasing the tailrace tunnel area is conducive to reducing the output swing of the large-capacity disturbed unit and the stable surge water level fluctuation of the surge chamber.