21
Distance protection
Uses measured voltage and current to assess an electrical distance or impedance characteristic.
Protection functions
Protection functions · 21G
Ground distance protection
Evaluates a distance characteristic for a phase-to-earth fault loop.
SLD / Schematic · 21G
What it represents
Evaluates a distance characteristic for a phase-to-earth fault loop.
The drafting record should connect this function to the phase and residual current references, VT circuit and protected line, then trace the ground distance zones and earth-loop compensation reference. Keep the complete designation and equipment tag together so that the SLD, relay logic and terminal schedule describe the same implementation.
The cited mapping is a public manufacturer example (SEL line protection documentation). Suffixes are not universal equivalences across products, and this reference supplies neither a protection setting nor certification of the selected scheme.
How to read it
- Identify the phase and residual current references, VT circuit and protected line.
- Trace the ground distance zones and earth-loop compensation reference.
Information to show or reference
- Label the phase and residual current references, VT circuit and protected line.
- Cross-reference the ground distance zones and earth-loop compensation reference.
- Retain the complete suffix, selected device tag and manufacturer manual revision.
A distinction that matters
Ground distance includes the ground-loop measurement treatment; it is not simply phase distance with a different alarm label.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
SEL 2022 Product and Solution Guide: published protection function tables
Explicit public manufacturer mapping of 21P to phase distance and 21G to ground distance in the protection feature tables.
SEL-321 phase and ground distance relay documentation
Public primary-source function or application mapping used to identify this designation; wording and drafting notes are original.
IEEE C37.2-2022: power-system device function numbers
Device-number and suffix convention. This page is not a reproduction of the full licensed standard.
About this graphic
This illustration was authored independently by Elora Grid to explain the concept. It is not reproduced from a customer drawing, an official standard graphic or a manufacturer CAD file. Its correspondence to an exact IEC or IEEE symbol identifier has not been certified.
SVG and DXF downloads contain this original artwork. DXF uses unscaled drawing units; a GA envelope supplies no product dimensions, clearances or fabrication information. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.
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