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The term switchgear, commonly used in association with the electric power system, or grid, refers to the combination of electrical disconnects and/or circuit breakers meant to isolate equipment in or near an electrical substation.
Location
Typically switchgear is located on both the high voltage, and the low voltage side of large power transformers. The switchgear located on the low voltage side of the transformers in distribution type substations, now are typically located in what is called a Power Control Center. Inside this building are typically smaller, medium-voltage (~15kV) circuit breakers feeding the distribution system. Also contained inside these Power Control Centers are various relays, meters, and other communication equipment allowing for intelligent control of the substation.
Housing
Switchgear for low voltages may be entirely enclosed within a building. For transmission levels of voltage (high voltages over 66 kV), often switchgear will be mounted outdoors and insulated by air, though this requires a large amount of space. A compact, though more costly form of switchgear is "gas insulated switchgear" (GIS), where the conductors and circuit breakers are insulated by pressurized sulfur hexafluoride gas.
At small substations, switches may be manually operated, but at important switching stations on the transmission network all devices have motor operators to allow for remote control.
Functions
One of the main basic functions of switchgear is protection: discrimination between circuit breakers enhances availability, that is to say continuity of service. The overall approach is termed coordination: the standards provide a framework for discrimination and cascading that protects the integrity of the power system and minimizes the scope of downstream outages.
External links
"Switchgear"