Electrical substations are among the most important installations in a power system. A substation receives electricity from generating stations or transmission networks, changes voltage levels where required, switches electrical circuits, isolates faulty sections, measures electrical quantities, and distributes power to outgoing transmission or distribution feeders. Substations are necessary because electrical power must move safely and efficiently from its source to consumers. Transmission substations generally operate at high or extra-high voltage, while distribution substations reduce voltage to levels suitable for local distribution networks and industrial consumers. Modern substations may use Air-Insulated Switchgear, or AIS , Gas-Insulated Switchgear, or GIS , or a hybrid arrangement. AIS is generally suitable where sufficient land is available, while GIS is frequently selected for urban, industrial, coastal, or space-restricted locations because of its compact arrangement. Moder...