Editing Substation (section)

=== Switchgear ===
High-voltage [[circuit breaker]]s are commonly used to interrupt the flow of current in substation equipment. At the time of interruption, current could be normal, too high due to excessive load, unusual due to a fault, or tripped by protective relays prior to anticipated trouble.{{sfn|Blume|2016|p=69}}  The most common technologies to extinguish the [[power arc]] from separating the conductors in the breaker include:{{sfn|Blume|2016|p=70}}
*Air at atmospheric pressure (air-insulated switchgear (AIS)), which is the most common worldwide.{{sfn|Twomey|2018|p=12}} Air is the cheapest insulator and is easy to modify, but AIS takes up more space, and leaves equipment exposed to the outside environment.{{sfn|Twomey|2018|p=13}} One drawback of AIS is the visual impact of a larger substation with overhead power lines entering and exiting, which may be unacceptable in scenic or urban areas.{{sfn|Glaubitz|2018|p=363}} AIS requires additional bracing in a seismically active area, and emits more [[electromagnetic fields]] and noise than alternative technologies.{{sfn|Glaubitz|2018|p=365}}
*Gas (gas circuit breaker (GCB) or gas-insulated switchgear (GIS)), most commonly [[sulfur hexafluoride]] (SF<sub>6</sub>) or a mixture of gases including SF<sub>6</sub>.{{sfn|Twomey|2018|p=12}} Although it is the most expensive, these gases are a much more effective insulator than air.{{sfn|Twomey|2018|p=13}} GIS require only 10 to 20 percent of the land area as AIS,{{sfn|Glaubitz|2018|p=361}} which can save on land acquisition cost in urban areas,{{sfn|Twomey|2018|p=13}} and allow the substation to be built at the exact location where its power is being used in an industrial or urban area—which can be a significant cost savings. On the generation side, GIS can be installed closer to the generator which allows cost savings in cabling, bus duct connections, and civil construction and can increase reliability.{{sfn|Glaubitz|2018|p=363}} GIS can replace AIS if power requirements increase without requiring additional land area.{{sfn|Glaubitz|2018|p=363}} Additionally, GIS is commonly installed in an enclosed building that keeps the equipment protected from pollution and salt.{{sfn|Twomey|2018|p=13}}{{sfn|Glaubitz|2018|p=363}} Unless the substation is often used for switching, maintenance cost can be very low or even zero for many years.{{sfn|Glaubitz|2018|p=368}}  Because SF<sub>6</sub> turns to solid around {{convert|-40|C}}, in some climates these circuit breakers require heaters to function in extremely cold weather.{{sfn|Blume|2016|p=72}} SF<sub>6</sub> has been used in switchgear since the 1960s.{{sfn|Nixon et al.|2018|p=329}}
*[[Mineral oil]] (called OCB for oil circuit breaker) provides a high resistance between the opened contacts, effectively stopping the flow of current.{{sfn|Blume|2016|p=70}} Although oil circuit breakers are suitable for a wide range of voltages, the oil becomes contaminated during the suppression of arcs and must be filtered or replaced periodically.{{sfn|Blume|2016|p=71}}
*[[Vacuum]] is a better insulator than air but less than gas or oil. Vacuum circuit breakers (VCB) are smaller than air circuit breakers and are commonly used in distribution and other switchgear under 35kv.{{sfn|Blume|2016|p=72}}
*Mixed, including both gas and air insulation. Although it’s the least common option{{sfn|Twomey|2018|p=12}} it can be useful when an air-insulated substation needs to be expanded but there is very limited location for additional construction.{{sfn|Twomey|2018|p=13}}

[[Recloser]]s are similar to breakers, and can be cheaper because they do not require separate protective relays. Often used in distribution, they often are programmed to trip when the amps exceed a certain amount over a period of time. Reclosers will attempt to re-energize the circuit after a delay. If unsuccessful for a few times, the recloser will have to be manually reset by an electrical worker.{{sfn|Blume|2016|p=74}}