7
Hydrotherrnal Coordination
7.1 INTRODUCTTON
The systematic coordination of the operation of a system of hydroelectric generation plants is usually more complex than the scheduling of an all-thermal generation system. The reason is both simple and important. That is, the hydroelectric plants rnay very well be coupled both electrically (Le., they al1 serve the same load) and hydraulically (i.e., the water outflow from one plant rnay be a very significant portion of the inflow to one or more other, downstream plants). No two hydroelectric systems in the world are alike. They are all different. The reasons for the differences are the natural differences in the watersheds, the differences in the manmade storage and release elements used to control the water flows, and the very many different types of natural and manmade constraints imposed on the operation of hydroelectric systems. River systems rnay be simple with relatively few tributaries (e.g., the Connecticut River), with dams in series (hydraulically) along the river. River systems rnay encompass thousands of acres, extend over vast multinational areas, and include many tributaries and complex arrangements of storage reservoirs (e.g., the Columbia River basin in the Pacific Northwest). Reservoirs rnay be developed with very large storage capacity with a few high-head plants along the river. Alternatively, the river rnay have been developed with a larger number of dams and reservoirs, each with smaller storage capacity. Water rnay be intentionally diverted through long raceways that tunnel through an entire mountain range (e.g., the Snowy Mountain scheme in Australia). In European developments, auxiliary reservoirs, control dams, locks, and even separate systems for pumping water back upstream have been added to rivers. However, the one single aspect of hydroelectric plants that differentiates the coordination of their operation more than any other is the existence of the many, and highly varied, constraints. In many hydrosystems, the generation of power is an adjunct to the control of flood waters or the regular, scheduled release of water for irrigation. Recreation centers rnay have developed along the shores of a large reservoir so that only small surface water elevation changes are posible. Water release in a river rnay well have to be controlled so that the river is navigable at al1 times. Sudden changes, with high-voIume releases of water, rnay be prohibited because the release could result in
