ELECTRIC SYSTEM GENERAL

The electric systems in the United States and Canada are interconnected, forming a network of electric facilities all across the continent. It is difficult to distinguish the electric system of one company from neighboring utilities. Figure 2.1 is a single-line diagram showing schematically a portion of an elementary electric system. Most electric utility companies will have many generating stations supplying a very large, complex, and intricate network of transmission and distribution circuits.

Figure 2.1: Single- line schematic diagram of a portion of an elementary ac electric system

The electric system in Fig. 2.1 has nuclear, fossil-fired, and hydroelectric generating stations. The bulk of the electric energy in the United States is generated in fossil-fired steam turbine-driven generating stations using coal, natural gas, and oil fuel. Hydroelectric generating stations using water pressure to turn a turbine have been constructed at most of the sites where there is sufficient waterfall to economically generate electricity. Nuclear generating stations use the heat from an atomic chain reaction to generate steam to turn a turbine generator.

Most electric energy is generated at a voltage in a range of 13,200 to 24,000 volts. The voltage is raised to transmission levels in a transmission substation located at the generating station. Transmission substations N, F, and H, shown schematically (Fig. 2.1), serve this purpose. Transmission circuits or lines operating at 138,000 to 765,000 volts deliver the energy to the load area. Transmission substations A, B, and C (Fig. 2.1) adjacent to the load area reduce the...