One-line diagram

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A typical one-line diagram with annotated power flows. Red boxes represent circuit breakers, grey lines represent three-phase bus and interconnecting conductors, the orange circle represents a generator, the green spiral is an inductor, and the three overlapping blue circles represent a power transformer.
A typical one-line diagram with annotated power flows. Red boxes represent circuit breakers, grey lines represent three-phase bus and interconnecting conductors, the orange circle represents a generator, the green spiral is an inductor, and the three overlapping blue circles represent a power transformer.

In power engineering, a one-line diagram is a simplified notation for representing a three-phase power system.[1] The one-line diagram has its largest application in power flow studies. Electrical elements such as circuit breakers, transformers, capacitors, bus bars, and conductors are shown by standardized schematic symbols.[1] Instead of representing each of three phases with a separate line or terminal, only one conductor is represented.

The theory of three-phase power systems tells us that as long as the loads on each of the three phases are balanced, we can consider each phase separately.[2] In power engineering, this assumption is usually true (although an important exception is the asymmetric fault), and to consider all three phases requires more effort with very little potential advantage.[3]

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

A secondary advantage to using a one-line diagram is that the simpler diagram leaves more space for non-electrical, such as economic, information to be included.

[edit] References

  1. ^ a b McAvinew, Thomas & Mulley, Raymond, Control System Documentation, ISA, p. 165, ISBN 1556178964 
  2. ^ Electrical Power Systems, Pergamon, p. 4, ISBN 0-08-021729-X 
  3. ^ Tleis, Nasser (2008), Power System Modelling and Fault Analysis, Elsevier, p. 28, ISBN 978-0-7506-8074-5 
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