# Grid equivalent source

Canonical URL: https://eloragrid.ai/symbols/grid-equivalent-source
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: EQ SRC
Drawing use: SLD
Reference families: IEC, IEEE / ANSI

A voltage source behind an impedance used in study diagrams to represent the external network at a defined fault level.

## In plain English

### What does Grid equivalent source mean?

A grid equivalent source represents the upstream network in load flow, short circuit and stability studies as an ideal voltage source behind an impedance. The impedance is calculated from the declared fault level and X/R ratio at the connection point, often with separate maximum and minimum cases.

### A simple example

Study single-line diagrams draw it as a circle with a sine wave followed by an impedance element, labelled with the fault level in MVA or kA and the X/R ratio. Microgrid studies use it to test both strong and weak network conditions before islanding scenarios are modelled.

### What the drawings help you do

The equivalent is only valid near the declared fault level; it cannot represent upstream dynamics such as voltage control or frequency response unless additional models are attached. The symbol does not tell you which study case it belongs to.

### This particular reference

A voltage source behind an impedance used in study diagrams to represent the external network at a defined fault level. A grid equivalent is a study model; a utility grid connection symbol represents the real supply on construction drawings.

### Terms

- Terminal: An identified point where a conductor connects.
- Rating: A value stating the conditions for which equipment is specified.
- Schematic: A drawing showing function and connections rather than physical appearance.

Concept diagram: Identify the device and form → Read the connections and state → Check the equipment reference
A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram.

- [IEC graphical symbols for diagrams](https://tc3.iec.ch/tc-activity/graphical-symbols-for-diagrams/)
- [IEEE/ANSI 315-1975: graphic symbols for electrical and electronics diagrams](https://standards.ieee.org/ieee/315/515/)


## What it represents

A grid equivalent source represents the upstream network in load flow, short circuit and stability studies as an ideal voltage source behind an impedance. The impedance is calculated from the declared fault level and X/R ratio at the connection point, often with separate maximum and minimum cases.
Study single-line diagrams draw it as a circle with a sine wave followed by an impedance element, labelled with the fault level in MVA or kA and the X/R ratio. Microgrid studies use it to test both strong and weak network conditions before islanding scenarios are modelled.
The equivalent is only valid near the declared fault level; it cannot represent upstream dynamics such as voltage control or frequency response unless additional models are attached. The symbol does not tell you which study case it belongs to.

## How to read it

- Read both the fault level and X/R ratio.
- Check whether the drawing shows maximum or minimum fault case.

## Information to show or reference

- State fault level, X/R ratio and voltage.
- Show the impedance element.
- Reference study case.

## Important distinction

A grid equivalent is a study model; a utility grid connection symbol represents the real supply on construction drawings.

## Facts

- Model: Voltage source behind impedance
- Parameters: Fault level and X/R ratio
- Use: Power system studies
- Preview: Independent educational illustration; consult the applicable standard and project legend for the exact graphic

## Public references

- [IEC graphical symbols for diagrams](https://tc3.iec.ch/tc-activity/graphical-symbols-for-diagrams/) — IEC. IEC graphical symbol context for sources and impedances.
- [IEEE/ANSI 315-1975: graphic symbols for electrical and electronics diagrams](https://standards.ieee.org/ieee/315/515/) — IEEE Standards Association. IEEE/ANSI graphic-symbol context for sources.

## Graphic scope

Independent original educational concept illustration by Elora Grid. Not a certified standards graphic or manufacturer footprint. Unitless; not to scale. Original artwork licence: https://creativecommons.org/licenses/by/4.0/. Publisher material is linked only.