Study On Electromechanical Disturbance Propagation In Power Systems Based On Distributed Fluid Network

Connection of the power grids, which improves the system economic operation, is the development trends in the countries of the whole world, however, the probability of various disturbance subjected to the power grids gradually increases. After the power system in normal operating state suffered by the disturbance, the relationship between the mechanical power and the electromagnetic power of the generator lose balance, thus the generator operates into a dynamic process. Through the use of the synchronized phasor measurements (PMU) with the help of the global positioning system (GPS), rotor angles of the generators in different places show a transmission process, not changing at the same time. The spread of the mechanical and electrical disturbance in the power system may cause many faults and these faults may also show the evolution of the chain reaction, which makes the power system lose stability. With the installed capacity of the wind power currently increasing, the stability of the power grid is affected increasingly by the intermittent of the output power of the wind generators, which requires the accurate grasp of the transmission characters of the mechanical and electrical disturbance in the power system and the deep study of the suppression measures of the mechanical and electrical disturbance.This paper analyzes the research situation of the electromechanical disturbance propagation in the power system and reviews the development process of electromechanical dynamic based on continuum model. Based on the thinking of time-domain modeling of distributed fluid pipeline network, a new simulation model for the research on the propagation of electromechanical disturbance in power systems is posed, which can reflect topological structure of power systems and consider internal reactance of generators reasonably, is proposed. Applied the proposed model to a simulation system composed of5generators and comparing the simulation results with those by PSS/E, the correctness of the distributed fluid network model is proved and the remarkable influence of internal reactance of generators on the propagation characteristics of electromechanical disturbance is revealed. According to the basic equations of electromechanical disturbance propagation, the transient process of electromechanical disturbance propagate is studied by analytical solution. When the initial disturbance is the form of step function, electromechanical disturbance transient transition process is composed of a series of ladder waver with linear superposition which have a specified delay. The characteristics of electromechanical propagation in the power grid including Doubly Fed Induction Generator (DFIG) are studied. Aerodynamic model and wind model, which are suitable for the study of electromechanical dynamics, are defined in Power System Simulation Software (PSS/E), and the characteristics of electromechanical dynamics which are effected by DFIG, are simulated and studied, when the initial disturbance is the change of wind speed. The results prove that, as a result of the decoupled control strategy, DFIG has little effect on the time response of the electromechanical disturbance in the propagation process, but makes the amplitude of disturbance larger. Compared with the variation speed of voltage phase angle of the bus connected common generator, the bus connected DFIG is faster, and then the serious consequence will be taken place.Results of the presented research offer a new idea for the research on propagation of electromechanical disturbance in power system. The factors which effect the electromechanical disturbance propagate are analyzed by analytical solution, and the analytical solution is better to insight into the nature of the electromechanical dynamicin powersystem. A new thinking which can be used to control the propagation of the electromechanical disturbance is provided. The studies of electormechinal disturbance progation in power system including wind turbines have a special theoretical reference value of anysizing the impact performance to the power grid caused by wind turibe machines.