ELECTRICAL ENGINEERING
DRAWING
BY
JULIUS ASIIMWE
jasiimwe@kab.ac.ug
Power Systems Diagrams
Power Systems Diagrams
• In power engineering, a One-Line Diagram also known as
Single-Line Diagram (SLD) is a simplified notation for
representing a three-phase power system.
• 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.
• Instead of representing each of three phases with a separate
line or terminal, only one conductor is represented. It is a form
of block diagram graphically depicting the paths for power
flow between entities of the system.
How to Read single-Line Diagrams
• We use universally accepted electrical symbols to
represent the different electrical components and
their relationship within a circuit or system.
• To interpret single-line diagrams, you first need to be
familiar with the electrical symbols.
• This chart shows the most frequently used symbols.
When interpreting a single line diagram, you should always start at the top where
the highest voltage is and work your way down to the lowest voltage. This helps to
keep the voltages and their paths straight.
Typical Single Line Diagram
More Examples of Typical Power Systems Diagrams
Star-Delta Starter Control Circuit
Star-Delta Starter Power
Forward-Reverse Control Circuit