Graphical symbols

A single-line diagram (SLD) draws each device as a graphical symbol. The symbols of the design's SLD are simplified from IEC 60617, and the SLD's legend names each one (Figure 1). A reader who knows the symbols can follow a circuit from the line through its bay to the bus, and from the transformer to the medium-voltage (MV) feeders.

Read first: Single-line diagram (SLD)

1The legendCopy link to The legend

The legend of the SLD lists the symbols the drawing uses, with the name of each device (Figure 1). A series device sits on the conductor, such as the circuit breaker, the isolator, the isolator with its earth switch, the current transformer and the fuse. A device at the end of a branch hangs off it, such as the voltage transformer and the surge arrester, each with its earth. The transformer is drawn as its windings, with the vector group beside it, and its neutral grounding resistor (NGR) in its neutral.

2Symbols and designationsCopy link to Symbols and designations

On the drawing a symbol carries the device's designation before its name (Single-line diagram (SLD), The order in a bay). In the IEC + CEA / CBIP set the circuit breaker is −Q0, the bus isolators −Q1 and −Q2, and the line isolator −Q9 with its earth switch −Q8. The current transformer is −T1, the capacitor voltage transformer −T5 and the surge arrester −F1. In the ANSI / IEEE set the breaker is 52 and the disconnect switches 89, the device function numbers of IEEE C37.2-1996. Sketch mode's SLD library offers IEC symbols for edits to the drawing.