ABSTRACT
The electric power grid is organized into three major segments: generation, transmission, and distribution. Historically, turbine-driven central station generators convert thermal or hydro energy into electricity, step-up transformers raise the voltage to bulk power transmission levels, where the electrical power is transmitted across wide areas. Transmission voltages are dropped to primary distribution levels (typically, 4–34 kV). Primary distribution lines move the power to industrial, commercial, and residential grid customers. Distribution transformers step the voltage down to secondary distribution (service) levels. Most customers purchase electric power at the service level, and then distribute it to loads on their premises. Some larger grid customers purchase power at the primary distribution level. A few very large customers are fed directly from the transmission grid. Figure 11.1 shows a portion of a typical substation that converts the voltage from transmission levels to primary distribution level. Representative substation with overhead bus and substation transformer. https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9781315214221/b8e2919a-8226-453c-b80b-0424e3c7347d/content/fig11_1.jpg"/>
