Editing Single-line diagram (section)

==Balanced systems==
The theory of three-phase power systems tells us that as long as the [[Electrical load|load]]s on each of the three phases are balanced, the system is fully represented by (and thus calculations can be performed for) any single phase (so called ''per phase analysis'').<ref name=guile_paterson>
{{citation
| first1 = A.E. | last1 = Guile
| first2 = W.| last2 = Paterson
| title = Electrical Power Systems
| edition = 2nd
| page = 4
| publisher = Pergamon
| isbn = 0-08-021729-X
| year = 1977}}</ref><ref name="RAMARKURUSEELAN2013">{{cite book | author1 = S. Ramar | author2 = S. Kuruseelan | date = 25 March 2013 | title = Power System Analysis | publisher = PHI Learning Pvt. Ltd. | pages = 8 | isbn = 9788120347335 | oclc = 1026831292 | url = https://books.google.com/books?id=ahntULiMFgwC&pg=PA8}}</ref> In power engineering, this assumption is often useful, and to consider all three phases requires more effort with very little potential advantage.<ref>
{{Citation
| first = Nasser | last = Tleis
| title = Power System Modelling and Fault Analysis
| publisher = Elsevier
| year = 2008
| page = 28
| isbn = 978-0-7506-8074-5}}</ref> An important and frequent exception is an [[asymmetric fault]] on only one or two phases of the system. 

A single-line diagram is usually used along with other notational simplifications, such as the [[per-unit system]].

A secondary advantage to using a single-line diagram is that the simpler diagram leaves more space for non-electrical, such as [[Energy economics|economic]], information to be included.