Editing Single-line diagram (section)

{{Short description|Simplest symbolic representation of an electric power system}}
[[Image:One-line diagram.svg|thumb|right|300px|A typical single-line diagram with annotated power flows. Red boxes represent [[circuit breaker]]s, grey lines represent three-phase bus and interconnecting conductors, the orange circle represents an [[electric generator]], the green spiral is an [[inductor]], and the three overlapping blue circles represent a double-wound [[transformer]] with a tertiary winding.]]
In [[power engineering]], a '''single-line diagram''' ('''SLD'''), also sometimes called '''one-line diagram''', is a simplest symbolic representation of an electric power system.{{sfn|Oliver|1991|p=38}}<ref name=csd>
{{citation
| first1 = Thomas | last1 = McAvinew
| first2 = Raymond | last2 = Mulley
| title = Control System Documentation
| page = 165
| publisher = ISA
| isbn = 1-55617-896-4
| year = 2004}}
</ref> A single line in the diagram typically corresponds to more than one physical [[Electrical conductor|conductor]]: in a [[direct current]] system the line includes the supply and return paths, in a [[three-phase]] system the line represents all three phases (the conductors are both supply and return due to the nature of the [[alternating current]] circuits).{{sfn|Oliver|1991|p=38}}   

The single-line diagram has its largest application in [[Power flow study|power flow studies]]. Electrical elements such as circuit breakers, transformers, capacitors, [[Busbar|bus bars]], and conductors are shown by standardized schematic symbols.<ref name=csd/> Instead of representing each of three phases with a separate line or terminal, only one conductor is represented. 

It is a form of [[block diagram]] graphically depicting the paths for power flow between entities of the system. Elements on the diagram do not represent the physical size or location of the electrical equipment, but it is a common convention to organize the diagram with the same left-to-right, top-to-bottom  sequence as the [[switchgear]] or other apparatus represented. A single-line diagram can also be used to show a high level view of conduit runs for a [[Power-line_communication|PLC]] control system.