What is SLD in Electrical Power Systems?

SLD is a short form of the term Single Line Diagram. It is also called as One Line Diagram. SLD is a very simplified representation of electrical systems. Basically it is a combination of lines, Symbols and block diagram. Here is an example, how a typical single line diagram is.

SLD for A Balanced Three Phase Power System

For a balanced 3 phase power supply, only a single line is used to represent three phase conductors and one neutral conductor. From this we can get an idea that four lines are represented by just one line. This makes representation of electrical systems simple. 

SLD for An Unbalanced Three Phase Power System

But for unbalance three phase power systems, each phase is represented by positive sequence, negative sequence and zero sequence systems. In this case SLD becomes complex. Hence it is very convenient to use SLD for balanced power systems.

Let’s see these following symbols used in SLD and their meaning.

Advantages of SLD

It provides clarity about given system and enables swift action.

SLD is a great way to communicate the action plans and installation plans related to the power system.


Updating SLD is also relatively easy and important. Usually electrical power system changes over time depending upon the demand of that region. Hence accordingly it is very important to update the SLD of that particular system, in accordance with the changes.

Leave a Comment

Your email address will not be published.