The North American electric power transmission system has been described as the largest, most complex machine ever built by humanity. It is a massive network of generating stations, transmission lines, substations, distribution lines, motors, and other electrical loads all interdependently linked for the conversion, transportation, and control of electrical energy. Approximately 60 percent of all energy utilized in the United States passes through the interconnected electric power system. The major goal of the system is to most efficiently and reliably deliver electric power from generating stations to residential, commercial, and industrial consumers.

A small portion of the power system is depicted in Figure 1. The flow of energy is as follows: at generating stations, mechanical, chemical, or some other form of energy is converted into electricity, most often using a synchronous generator. The electrical output from the generator is converted...