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FIGURE 1.6 Illustrative analogy of electric transmission and distribution. Unlike a set of rigid drive shafts (above) that move power from generators to loads, AC power transmission and distribution systems are more accurately thought of in terms of a series of coil springs of varying stiffness through which power is transmitted by twisting (below). Since these links are not rigid, under some circumstances they can exhibit complex oscillatory behavior, or even become so tangled that they can no longer transmit power.

advantage might sabotage its competitor’s equipment, and in the process compromise the integrity of the system. Until the pernicious actions of Enron traders were revealed, few would have given such a possibility a second thought. With tighter oversight and greater awareness within the industry, plus FERC’s increased emphasis on market monitoring, such activity is probably unlikely, but the potential for it should not be ignored. The possibilities include, for example, (1) generators in one independent system operator (ISO) capturing transfer rights on tie-lines between control areas in order individual parts cannot be selected to increase congestion at those facilities and thereby maintain local market power, or (2) large buyers creating transient disturbances on the system in an effort to reduce the number of other buyers, thereby lowering system load and price. A simplified model illustrates how two or more small, physically separated generators acting together might have their supply frequencies altered and produce resonant phenomena that might cause protective devices on other large competi-



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