Control of electric power systems

commercial and industrial type. It must withstand with reasonable security the capricious forces of nature. In an age of high energy costs it is called upon to transform the prime energy resources into electric form with an optimum overall efficiency. The control functions are obviously many and varied. Some control and decision processes, exemplified by the optimal utilization of the controlled flow of river systems involve dynamics with month-long time constants. Other phenomena, like the transients on the transmission lines following lightning strikes, run their course in a few milliseconds. The slower control processes are normally handled by computer-assisted human operators. The faster control functions are trusted to fully automatic control systems of either open or closed-loop nature. The objective of this article is first to outline briefly the basic functional features of a power system and, secondly, describe some of the more important controls required for its satisfactory operation. Finally some of the more relevant research and development areas are identified and discussed. Fig. 1 shows a one-fine diagram of a section of a larger system. The electric power is produced in the generators. transformed to an appropriate voltage level in the transformers and then via the buses sent out on the transmission fines for final distribution to the loads. Via tie-lines the system is connected to neighboring systems belonging to the same pool. Fig. 1 does not show the low-voltage distribution portion of the system, which contains the majority of the load objects. For most important system studies it is sufficient to use lumped or composite representations of the loads. The load symbols in Fig. 1 are of the latter type. The circuir breakers permit the tripping of faulty components and also sectionalizing of the system. High voltage dc (HVDC) is being used in special cases. However, the vast majority of the world's electric power is being generated, transformed, transmitted and distributed as high voltage ac (HVAC) of the threephase variety. Collectively the generators, transformers, buses, lines and loads constitute the power network or grid.