Editing Substation (section)

===Switching station===
A switching station is a substation without transformers and operating only at a single voltage level. Switching stations are sometimes used as collector and distribution stations. Sometimes they are used for switching the current to back-up lines or for parallelizing circuits in case of failure. An example is the switching stations for the [[Inga–Shaba|HVDC Inga–Shaba]] transmission line.

A switching station may also be known as a switchyard, and these are commonly located directly adjacent to or nearby a [[power station]]. In this case the generators from the power station supply their power into the yard onto the generator bus on one side of the yard, and the transmission lines take their power from a Feeder Bus on the other side of the yard.

An important function performed by a substation is [[switch#Power switching|switching]], which is the connecting and disconnecting of transmission lines or other components to and from the system. Switching events may be planned or unplanned. A transmission line or other component may need to be de-energized for maintenance or for new construction, for example, adding or removing a transmission line or a transformer. To maintain reliability of supply, companies aim at keeping the system up and running while performing maintenance. All work to be performed, from routine testing to adding entirely new substations, should be done while keeping the whole system running.
<gallery mode="packed">
File:Grand Coulee Dam electrical switchyward.jpg|Switchyard at [[Grand Coulee Dam]], United States, 2006. This is a 500 kV switchyard.<br/>
File:Umspannwerk Stuttgart-Seewiesen.jpg|Former high-voltage substation in Stuttgart, Germany, now 110&nbsp;kV switching station. The 220&nbsp;kV level is eliminated for grid simplification.<br/>
File:E11445 - DPLA - 59d7213736b68ece2fbcf348197aecda.jpg|230&nbsp;kV High-voltage switching station in Washington, United States
</gallery>
Unplanned switching events are caused by a [[fault (power engineering)|fault]] in a transmission line or any other component, for example:
*a line is hit by lightning and develops an [[Electric arc|arc]],
*a [[Transmission tower|tower]] is blown down by high wind.
The function of the switching station is to isolate the faulty portion of the system in the shortest possible time. De-energizing faulty equipment protects it from further damage, and isolating a fault helps keep the rest of the electrical grid operating with stability.<ref>{{cite web |title=Transformer Fire Video |url=http://www.metacafe.com/watch/39058/transformer_fire_video/ |website=metacafe |publisher=User Eagle Eye |access-date=4 February 2016}}</ref>