Single-line diagram

Electrical elements such as circuit breakers, transformers, capacitors, bus bars, and conductors are shown by standardized schematic symbols.

A one-line diagram can also be used to show a high level view of conduit runs for a PLC control system.

For sufficiently large systems, these points represent physical busbars, so the diagram nodes are frequently called buses.

When using the method of symmetrical components, separate one-line diagrams are made for each of the positive, negative and zero-sequence systems.

For example, in general a generator will have different positive and negative sequence impedance, and certain transformer winding connections block zero-sequence currents.

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 an electric generator , the green spiral is an inductor , and the three overlapping blue circles represent a double-wound transformer with a tertiary winding.