Research On Vibration Characteristics & Stability Of Hydro-mechanical-electrical System In Hydropower Station

Research on vibration characteristics and stability of hydro-mechanical-electrical system is related to the dynamic characteristics of hydraulic system, mechanical system and electrical system, mathematical model of each system and relating methods. Less achievement concerned this problem is yielded at home and abroad.With theoretical analysis, numerical computation, test simulation, the mathematical model for vibration analysis of hydro-mechanical-electrical system has been established. Further study on vibration characteristics and stability of hydro-mechanical-electrical system has been performed in this dissertation. Some new ideas and the main achievement are as follows:1^st. The practical elastic models of water flow vibration in pressurized pipelinesThe linear and nonlinear models that describe the vibration characteristics of water flow in pressurized pipelines have been deduced based on variation theory and Ritz-Galerkin approximation method. These models are easy to be decoupled and used to comprehensive analysis of hydro-mechanic-electrical system. Each vibration mode of water flow in pressurized pipelines is given actually with corresponding ordinary differential equations by means of decoupling. The practical use of these models has been analyzed, and the minimum order of elastic models corresponding to the pressurized pipelines with different length has been given considering the effect of low frequency oscillation in electrical system.2^nd. Study on self-excited vibration of reversible pump-turbineDue to the flow characteristics of possible "S" characteristic zone in reversible pump-turbine's operational curve, the mathematical equations for self-excited vibration of single unit or two units in pump/turbine condition have been established, and its approximate analytic solution has been deduced. Considering unit running in the " S " characteristic zone, a case study for free vibration analysis has been given, and the oscillating curve has been given by characteristic method. The study indicates that, the numerical result of oscillation frequency and amplitude of self-excited vibration is identical with theoretical analysis. The dangerous of self-excited vibration has been emphasized.3^rd . Influence analysis of vibration characteristics of water elastic to system's stabilityThe relation between possible zero eigenvalues and state variables in stability analysis has been studied based on linear system theory and relevant factor method.The difference of stability zone while elastic model of water flow or stiff model is adopted, has been studied in detail. The results indicate that, the stability zones have cross phenomena and area of stability zone is smaller than that of stiff model. The difference goes more serious with the increase of pipe's length.By use of elastic model with different order, the proper order is chosen based on pipes' length in order to have actual stability analysis combined with the effect of electrical system.The effect of water flow's vibration characteristics to low frequency oscillation's damping in electrical system, has been analyzed in a case study with the vibration characteristics of water flow. It is known that, considering the higher vibration characteristics,total positive damping is increasing with smaller criteria time constant Tw, while totalpositive damping is decreasing with larger Tw.4th. Influence analysis of electrical system with different load to system's stability and damping of low frequency oscillation by means of test simulation and numerical computationBased on the built experimental facility, simulation test has been finished considering different operational mode and load characteristics. Combined with case study and test simulation, it is acknowledged and proved directly that impact of large net is beneficial to operating stability, and the stability and regulation performance of unit running with dynamic loads is better than static loads. The numerical analysis is identical with test result.5th. Study on vibration characteristics and stability in two units sharing a common tail-tunnelMathematic model for stability analysis of expanding unit connection has been established. Given a system with two units having hydraulic coupling and electrical coupling (expanding unit connection), the distribution discipline between two units has been studied. It is showed that, the influence on low frequency oscillation is identical with larger increased damping on one unit or smaller increased damping on two units. The possibility and danger of resonance among multi-systems has been proposed with the study on resonance between hydro-mechanic system and electrical system.