Distribution Equipment

electric-power equipment designed to receive electric power from power-station generators, from transformers, or from converters in converter substations and to distribute it among individual consumers. It comprises electric switches, disconnecting switches, current and voltage transformers, measuring instruments, buses, dischargers, and electric reactors. In order to allow maintenance of the distribution equipment or portions of the electric-power network without interruption of service, the bus system is divided into sections.

Equipment installations may be classified according to structural design as indoor or outdoor. Indoor installations are generally used for voltages up to 10 kilovolts (kV). They have all apparatus and current-carrying parts located inside a building. Where the atmosphere is heavily polluted or where deposits of dust, chemical products, or salt from the ocean may settle on insulators and act as electric conductors, indoor installations are used for voltages up to 220 kV. Outdoor installations are primarily used for voltages of 35 kV and higher. They have all apparatus mounted outside of buildings.

In order to reduce the area occupied by electric distribution equipment, shorten the time for assembly and repairs, reduce the operating costs, and increase safety during servicing, all equipment units operating at voltages up to 35 kV are commonly mounted at the factory in metal cabinets or cases. In distribution equipment with voltages less than 10 kV, the current-carrying parts in such assemblies are insulated by means of ceramic insulators and air or by cast-epoxy insulation. Since the late 1960’s, compact, hermetically sealed assemblies have become popular for voltages up to 66 kV and higher in which sulfur hexafluoride (SF₆) at a pressure of several atmospheres serves as insulation.