Study On Mechanical And Electrical Vibration Of Hydraulic Generator Set In Three Gorges

With the development of power system, the structure of power system nowadaysis becoming more and more complex. The application of various electrical controllersand the union of large scale power network make the nonlinear vibration ofmechanical and electrical coupled systems and stability of power system a key factorto analyze the system thoroughly. Using the theory of nonlinear dynamics ofmechanical and electrical coupled systems and bifurcation theory of nonlinear system,based on the generator set in Three Gorges, the theoretical and numerical calculationare presented to analyze the stability and bifurcation phenomena with electromagneticparameter change. Major work and results obtained are as follows: (1) A review is given on the development and methods of analysis. A briefdepiction is given too on the basic concepts not only about the dynamic process ofpower system but also about the nonlinear vibration and bifurcation. (2) According to two different opinions : electromechanics and analytic dynamicsof mechanical and electrical systems, we obtained the same differential dynamicalequations of the whole system. It proved that the energy combined the mechanical andelectrical parts to a coupled system in which the variables affect each other. analyticdynamics of mechanical and electrical systems provides a useful tool for analysis ofnonlinear system. (3) We expatiated three kind of symmetry or asymmetry failure, which are threephase short-circuit, two phase short-circuit and one phase short-circuit, to find theinfluence on the vibration of system, currents and power angle. We also studied theinfluencing extent on system with different location where short-circuit take place.Then, we sought the law of initial frequencies and studied the transient responses ofcurrents and electromagnetic torque in out-of-phase synchronization. We got the curvebetween the angle of out-of-phase and maximum of transient torque. (4) Considering the co-action of turbine exciting and parameters of generator andelectric transmission line, we studied several kinds of special resonance phenomena inmechanical and electrical coupled system. We noted that power angle δ and angularvelocity of rotor ω4 are the key variables that linked other mechanical or electricalvariables and caused them to interact each other. (5) Through numerical calculation, we obtained the stability figure for wholesystem with two parameters changing simultaneously. We have tested the characterpoints by numerical calculation and find the law of eigenvalues of system. (6) Based on the theory of nonlinear normal modes, we reduced the dimension ofhigh dimension nonlinear system when it has two positive real eigenvalues. Thesimplified equations can reflect the dynamic behavior to some extent, which will behelpful for the future research.