A Single Line Diagram or SLD is a simple visual representation of three phase power systems.

In this post you’ll learn what is Single Line Diagram and why do we need it.

Our electrical power systems primarily contain three phases of AC circuits. All transmission lines, distributions lines, and power transformers are also three phases in nature. While analyzing these systems, the use of three lines (all three phases) makes the documentation work complex. For this reason, a single line diagram is used instead.

Consider the schematic diagram of a three-phase generator that feeds a three-phase motor load:

Let’s redraw the single line diagram for above case:

As you can see, the single line diagram is a clean representation of the overall system that provides the big picture of the entire power system. Even for a simple case like above, the SLD is useful, practically SLDs are used for power systems and substations containing thousands of components and devices.

Given below are 20 SLD symbols that components that are most important in Electrical and Electronics Engineering.