Study On The Characteristics Of Pump-turbine And Transient Process Based On The Curved Surface

Pumped storage stations are the inevitable products during the development of modern power gird. They also play the irreplaceable role in the power system. Especially under the large-scale development of green energy, pumped storage stations have various roles and show huge advantages in peak-clipping, valley-filling, spinning reserve as well as frequency and phase modulation. Therefore, it has a large improvement in terms of quality, flexibility and reliability of the electric system. The guaranty calculation of regulation is one of the key contents in design and operation of the pumped storage stations. However, there are still more than seven issues that are listed below:1) The expression of the characteristic plane curves of pump-turbines may lead to the result that the interpolation and iteration can not continue because of multiple values and corresponding issues.2) Differences between the characteristics of the applied turbine and the real machine may lead to the wrong results of the transient process.3) Because of the improper solution method, the complex boundary conditions of units may give no or wrong solution.4) It lacks a suitable way of computation for enormous pressure pulsation in the transient process.5) The optimization of guide vane closing law of pumped storage stations does not have a clear theoretical basis.6) The design theory of conventional hydropower surge tank may not be suitable for pumped storage stations.7) It is not clear that the influence of the layout and dimensions of the water system on the calculation results of transient process.Based on the previous research, this dissertation deeply discusses the first, third, fourth and fifth issues mentioned above. The main contents include the following aspects:1. Research on the B-spline surface construction for the complete characteristics of pump-turbineOn the basis of the modeling technique of B-spline curve and surface, a B-spline curved surface in On1'Q1'M' coordinate system is constructed for the representation of the complete characteristics of pump-turbine in the second chapter. It can be proved to eliminate the multi-valued and non-corresponding problems existed in the plane curves representation. The approach of curved surface reconstruction is used for five sets of characteristic data in different segments of water head. Also, the approximation accuracy to the data points and opening lines are analyzed by changing the number of gird along the direction of opening (u direction) and the distribution of parameters (u direction).2. Research on the mathematical model and solution method of transient process for pump-turbine sets on the base of the curved surface.The mathematical model for the pump-turbine sets of transient process is based on the characteristic curved surface in the third section. In this model, the speed error function ? is proposed for the equation solving, which takes ?=0as the criterion of the root. Directional derivative of ? is taken along the whole opening line which is divided into several regions. And the changes of the signs and the absolute values of the items composing the directional derivative among the regions are discussed to study the monotonicity and the signs at the search boundary of ? which are taken as the theoretical basis of unique solution and root-seeking.3. Research on the simplified simulation method of pressure pulsation during pump-turbine load rejection.By means of the contour lines of pressure fluctuation of the model pump turbine, the fourth part focuses on the simplified simulation method of pressure pulsation amplitude along with the condition trochoid in load rejection. In order to obtain the accurate pressure pulsation value of the operation point at each moment, there are two means employed in this dissertation:Firstly, empirical mode decomposition method (EMD) is used to decompose measured pressure fluctuation signal. In accordance with the results and the trend of pressure pulsation contour curves, the model test data are extended to the turbine breaking range and the reverse pump range. Secondly, a triangulation network is built between the two adjacent contour lines of pressure fluctuation to interpolate the pressure pulsation amplitude of the operation point according to the values of the triangular grid points.4. Research on the optimization of guide vane closing law based on the pump-turbine opening characteristicsThe last chapter firstly describes the general analytical method of the variation of the head square root (ie the sign of AX) within the time step. Secondly, according to the sign of?n1,?Q1'of each time step, the moving direction of operating points and the monotonicity of speed error function, the trajectories are classified into32cases, the existence of which can be proved through mathematics. Thirdly, the sign of AX in each case is discussed and the impact on?X from the changes of the angle of trajectory is analyzed. The accuracy of the theoretical analysis is verified by a few examples, through which the impacts on AX from the changes of angle of trajectory caused by the shape of opening line and the guide vane closing velocity are also analyzed. Finally, this chapter summarizes the above research and proposes the optimization idea of guide vane closing based on opening characteristics.