Research On The Transition Process Of Large Fluctuations For The Hydraulic Units Of Pressurized Diversion Power Station

During the load rejection of hydropower station,due to the emergency closure of guide vane,the load of generator changes rapidly and decreases to zero load,and the water flow torque increases rapidly.The larger torque change has a greater impact on the unit speed,and the speed increases rapidly.When the guide vane is closed,the unsteady flow phenomenon occurs in the pressure pipe due to the water inertia,resulting in larger water hammer and rapid increase of speed High and large variation of water hammer pressure brings great threat to the operation safety and stability of hydropower station.Therefore,it is of great significance to study the large fluctuation transition process of hydraulic units,which can not only ensure the reliability of equipment operation,but also reduce the investment of hydropower station.Based on the extensive reading and research of previous achievements,based on the theory of hydromechanics and transient flow,the paper uses the characteristic line method to study the whole diversion power generation system,and establishes the mathematical model of the whole diversion power generation system,including the mathematical model of each component of the mixed flow unit,the mathematical model of the pressure water transmission pipeline and the impedance surge chamber.Through the analysis of the power generation system,the paper presents a mathematical model of the whole diversion power generation system The research of system model,using MATLAB language programming,unifies each model into a whole.Combined with the engineering practice,the simulation calculation is carried out for a variety of representative working conditions in the large fluctuation transition process of a high head and pressure diversion power station.According to the calculation results,whether the minimum pressure of draft tube inlet,the change value of unit speed rise,the minimum surge water level of surge chamber,the allowable value of spiral case end pressure,the maximum surge water level of surge chamber and other parameters meet the design specifications are analyzed,and the optimal guide vane closing form and law are determined,so that all parameters are within a reasonable range,so as to ensure the safe and reliable operation of the equipment.In addition,through the sensitivity analysis of moment of inertia and penstock diameter,the improvement measures for the optimization of large fluctuation transition process are proposed.