SUBSTATION TYPES

An electrical substation is an installation with electrical equipment capable of interrupting or establishing electrical circuits and changing the voltage, frequency, or other characteristics of the electrical energy flowing in the circuits.

Transmission Substations. Figure 3.1 shows an alternating-current (ac) electric transmission substation located at an appropriate point in a network of transmission lines. The substation contains equipment used to sectionalize the electric transmission system when a fault or short circuit develops on one of the circuits. The defective circuit is switched out of service automatically and deenergized, protecting the remaining portion of the transmission network from trouble. The electric transmission system is designed to permit deen-ergizing of any one circuit without interrupting electric service to customers.

Transmission substations located at electric generating stations (Fig. 3.2) have power transformers designed to raise the voltage from generation value, usually in the range of

Figure 3.1: Transmission substation with four autotransformer, 445 MVA single-phase, 500/230/34.5 kV. One transformer is a spare. Circuit breakers in the substation are used to switch circuits and power transformers in and out of service. Series reactors in the foreground limit the fault current in the 34.5-kV circuits. (Courtesy ABB Power T&D Company Inc.)

Figure 3.2: Power transformers in an ac transmission substation located adjacent to generating station. Power transformers raise the generated voltage from 25 to 765 kV. Each single-phase transformer has a capacity of 317 MVA. The three-phase bank capacity is 950 MVA. The fourth transformer serves as a spare

13,200 to 25,000...