Research On Setting Criterion Of Tailrace Surge Chambers And Theoretical Construction Of Complete Characteristics Of Pump-turbines

The accidents during the operation of hydropower stations are mostly related to the hydraulic transients.Therefore,under the background of continuous large-scale development of hydropower(including pumped storage)in China,it is necessary to take full consideration of the internal characteristics of the hydraulic transients and to seek measures to improve the operating conditions of the units in the preliminary design stage of the power stations.Considering the key design parameters of the power station are uncertain and the complete characteristic curves of the hydraulic machinery are unavailable in the preliminary design stage,it is difficult to effectively carry out the numerical simulation of the hydraulic transients and judge the reasonableness of the setting of the surge chambers.Therefore,according to the design parameters of multiple power stations and the combination of theoretical deduction and numerical simulation,the regression analysis of the key parameters,the setting criterion of the tailrace surge chambers,the theoretical construction method of the complete characteristic curves of the reversible pump-turbines and the numerical simulations of the hydraulic transients are conducted.These research achievements can provide important scientific basis for engineering design.The main originalities of the thesis are as follows:1.A new setting criterion of the tailrace surge chambers that considers the dynamic head loss of long water conveyance system and the time sequence superposition of the water hammer vacuum(WHV)caused by the inertia of tailrace system,the velocity head vacuum(VHV)at the draft tube inlet and the head loss vacuum(HLV)of the water conveyance system is derived.And the mathematical model of the critical length of tailrace system(CLTS)is put forward.Through performing a comparative analysis with other criteria,the results show that taking more comprehensive influencing factors into account,the discriminant results obtained by the new setting criterion are more realistic.It can be used as a preliminary judgement standard for setting up a tailrace surge chamber in a conventional hydropower station or a pumped-storage power station with medium and low head.2.According to multiple sets of measured complete characteristic curves,explicit expressions for the characteristic parameters of characteristic operating point sets(COPs),as functions of specific speed and guide vane opening,are developed.And by combining with the regression analysis of COPs,the method for constructing the complete characteristic curves of the Francis pump-turbine is proposed based on the revised internal character analysis theory.This method effectively improves the simulation accuracy of the hydraulic transients in the preliminary design stage of pumped-storage power stations.3.Based on the statistical analysis of the relevant design parameters of 20 pumped storage power stations with high,medium and low water heads,the new empirical formulas of the key parameters,such as suction height,specific speed of turbine mode and pump mode and moment of inertia,are proposed.They can be used to analyze the hydraulic transients and judge the necessity of setting up surge chambers,thus providing scientific basis for the design of power stations.4.The method for predicting and simulating the hydraulic transients is presented for the lack of design data and complete characteristic curves of hydraulic machinery.And the practicability of this method is demonstrated by taking two domestic pumped storage power stations as examples.