The Relationship Between The Nonlinear Parameters Of Synchronous Generator And The Terminal Quantities And Its Application

With the development of power industry,the scale of power supply is expanding gradually,and the capacity of a synchronous generator is increasing rapidly,resulting in increasing influence on the entire power system.Accurate and reliable models and parameters are urgently needed in power system stability analysis,planning and design.The parameters of the conventional synchronous generator model are constants based on the assumptions of the ideal generator,which cannot fully consider the influence of nonlinear factors.However,there are many nonlinear factors of magnetic saturation,magnetic field distortion and so on existing in operating generators.And under various operating conditions,the degree of nonlinearity is also different,making quite different influence on the parameters especially on the reactance.The working conditions of a synchronous generator in a grid operation can usually be uniquely determined by a number of terminal quantities.Therefore,it is necessary to find the qualitative and quantitative relationship between the saturated reactance and different terminal quantities,which can be accurately and quickly applied to engineering practice of power system analysis.Fully taking into account the influence of a variety of nonlinear factors,this thesis uses Matlab to simulate a 300MW turbo-generator for the qualitative and quantitative relationship between the direct-and quadrature-axis synchronous reactances and the quantity of different terminal quantities.The main contents of the thesis are as follows.(1)Based on the calculated magnetic fields by Finite Element Method(FEM)and the phase diagram of the generator,the saturated reactance under different operating conditions is calculated,and the 2-D curves of the reactance variation with the different loads and different power angles are given.(2)The various 2-D curves of the reactance variation with the different terminal quantities are summed up and extended,in order to present the 3-D surface variation law of the saturated reactance.The method gives more intuitive and comprehensive characterization of the reactance variation.According to the actual given conditions of an engineering project,the appropriate combination of terminal quantities can be selected,and the corresponding saturated reactance value under a given operating condition can be quickly determined with this method.(3)The least squares method is used to fit the 3-D surface variation of the reactance,and hence obtains the new characterizations of saturated reactance with the different terminal quantities as the independent variables.Through the analysis and comparison of the different characterization errors,the practical characterization forms are determined for engineering applications.(4)By using the proposed characterization methods together with the analytical method,several steady-state behaviors of the generator are calculated,including the field current,the power angle characteristic curve,the V-shaped curve,the curve of field current vs.stator current and P-Q capacity diagram.Compared with the measured or the calculated results by FEM as the benchmark,accuracy of the proposed characterizations is verified.Compared with the traditional analytical method which uses the constant reactance value,this method can fully consider the influence of nonlinear factors on the saturated synchronous reactance under different operating conditions.The proposed method is flexible in its form and simple for practical application.