Electromechanical Wave Propagation in Large Electric Power Systems

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ECS-9709253 Thorp One of the results of deregulation and the creation of large independent system operators (ISO) is that the physical size of the system to be operated will be greatly increased. Systems will be larger both in terms of square miles and in electrical dimension. It is our premise that there are effects in such large systems that are not easily understood using existing models and that valuable understanding can be obtained by taking a macroscopic view of the system. As the number of buses reach tens of thousands and system dimensions are measured in thousands of miles, it is useful to imagine a distributed system with a contimuun of transmission, generation, and load. The phenomenon of electromechanical oscillations of generator rotors caused by faults and equipment outages is one of the most vexing problems facing the interconnected network operators . If the protection and control systems do not function as they are designed to do in the face of a disturbance, the disturbance can propagate over the network, and expose individual generators, or groups of generators to the danger of going 'out-of-step' with the rest of the network. If a sufficient number of generators lose synchronism in this fashion, a system black-out results, and very expensive, disruptive, and time-consuming restoration procedures have to be followed. These phenomena -familiarly knows as 'transient stability' studies-are the subject of the most important investigations in power system planning. The normal techniques for studying electromechanical transient phenomena are time-consuming and lead to voluminous outputs, and very often it is difficult to grasp the sense of the ensuing phenomena on a global scale. The proposal is to study the problem of electromechanical oscillations of generator rotors from an entirely different point of view . The power system with its transmission lines, generators, and loads is considered to be a continuum . When the power system spans entire continents, thi s is certainly a reasonable extrapolation. In doing so, we give up the detail associated with the motion of each machine rotor. In return , we gain and insight into the mechanisms by which the disturbances initiated by faults and other random events propagate in the continuum. When the problem is cast in this fashion, we find that very powerful techniques developed in others fields (wave propagation phenomena in plasma) can be brought to provide important insights and useful results. Power system engineers have long recognized that electromechanical disturbances propagate over the power network with finite speed, and exhibit dispersion phenomena. It is only in recent years that simultaneous measurement of rotor angles (through synchronized phasor measurements) has been made possible with the help of the GPS satellite system. Using these measurements over long distances, we expect to observe the traveling wave phenomena in actual power systems. The preliminary investigations confirm the presence of electromechanical traveling waves on the network treated as continuum. The research proposal identifies several important areas in which this work needs to be extended in order to produce results which could be used in designing next generation monitoring, protection and control systems on power networks.