Study On The Continuum Electromechanical Wave Model And Electromechanical Disturbance Propagation In Power Systems

Under normal operating conditions, an electrical power system is subjected to numerous random power impacts from sudden application or removal of loads continuously, as takes on electromechanical dynamic processes. Since electromechanical dynamics involve the motion of active power in the system, its propagation characteristics are closely related to the safe and steady operations of the overall system. Hence, study on electromechanical dynamic propagation is of especial importance in understanding the dynamic mechanisms of power systems intensively, performing dynamic stability analysis, and constructing a much safer and steadier control system.The continuum electromechanical wave model for power system is a completely innovative approach of exploring the electromechanical dynamic characteristics of large-scale power systems. In the continuum modeling technique, the generator is represented by the second order classical model and the power network by the quasi-steady state model, the power system is considered to be a continuum distributed transmission lines, generators, and loads continuously. The continuum model thinks that electromechanical disturbances propagate in the power system in the form of traveling wave, therefore, studies electromechanical disturbance propagation using wave motion theory.This dissertation attempts to study the continuum modeling theory and some fundamental physical characteristics about electromechanical disturbance propagation in a power system using the continuum model:(1) According to the idea of transverse vibrations of coupled particles to wave in the classical mechanics, it is established that the continuum model of the torsional vibrations of multi-mass damped disks, as is regarded as the mechanics basis of the continuum electromechanical wave model.(2) Based on the second order classical generator model, the nonlinear electromechanical wave equation for the continuum model in a chain power network is derived; whose similarity with the torsional wave equation of mechanical shaft is compared. In succession, the varying rules of the amplitude of electromechanical wave propagation are analyzed. Finally, the intrinsical mechanisms of attenuation or growth of electromechanical wave amplitude is revealed by a critical speed as it propagates in a uniform continuum power system.(3) Based on the linearized electromechanical wave equation, the characteristics of electromechanical wave propagation are studied. According to the Peterson's law, the effects of reflection and transmission of those lumped-parameter elements ~ generators to electromechanical wave propagation are also analyzed in the continuum power system. In the end, it validates that the electromechanical dynamics of a continuum power system could be expressed as the superposition of reflection and transmission processes of electromechanical wave at the location with non-uniform parameters.(4) The differential equations set of describing electromechanical wave propagation in a general lossless non-uniform continuum power system is established. The fundamental rules followed by the electromechanical wave propagation are studied while the per-unit length susceptance and the rotor inertia of the non-uniform continuum are power functions and slow-variation functions of spatial coordinate.(5) Based on the theoretical derivations, utilizing the combined Laplace-and Z- transformations, the analytical solutions, and the internal rules of the amplitude's growth or attenuation are presented using Bessel functions as the electromechanical disturbance propagates in a uniform chain discrete power network. Furthermore, the equivalence of the propagation velocity and the propagation time between the discrete- and continuum- models are analyzed and proved.(6) Through the simulation experiments of a standard test system—the modified New England 10-generator 39-bus, using the continuum modeling approach and the conventional modeling technique (PSS/E software package), it is studied that the propagation of electromechanical disturbance in the test power system, and both approaches could obtain almost the same results for the propagation velocity and the propagation time. It shows that the continuum model could be utilized to describe the electromechanical disturbance propagation in the power system.