A circuit breaker (within a switchgear enclosure) is the primary component that interrupts fault currents. The combination of equipment within the switchgear enclosure allows them to interrupt fault currents of thousands of amps. Other common types are oil or vacuum insulated switchgear. An effective although more costly form of switchgear is the gas-insulated switchgear (GIS), where the conductors and contacts are insulated by pressurized sulfur hexafluoride gas (SF 6). Switches may be manually operated or have motor drives to allow for remote control.Ī switchgear may be a simple open-air isolator switch or it may be insulated by some other substance. Oil insulated switchgear presents an oil spill hazard. Gas-insulated switchgear saves space compared with air-insulated equipment, although the equipment cost is higher. For higher voltages (over about 66 kV), switchgear is typically mounted outdoors and insulated by air, although this requires a large amount of space. Switchgear for lower voltages may be entirely enclosed within a building. This led to a further improvement, because the switching and measuring devices could be attached to the front, while the wiring was on the back. For reasons of fire protection, the wood was replaced by slate or marble. Later they were mounted on wooden panels. The first models were very primitive: all components were simply fixed to a wall. Switchgear is as old as electricity generation. Switchgear is further used to enhance system availability by allowing more than one source to feed a load. Switchgear also provides isolation of circuits from power supplies. One of the basic functions of switchgear is protection, which is interruption of short-circuit and overload fault currents while maintaining service to unaffected circuits.
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