21
Distance protection
Uses measured voltage and current to assess an electrical distance or impedance characteristic.
Protection functions
Protection functions · 21P
Phase distance protection
Evaluates an impedance characteristic for phase-fault loops on the protected circuit.
SLD / Schematic · 21P
What it represents
Evaluates an impedance characteristic for phase-fault loops on the protected circuit.
The drafting record should connect this function to the phase CT and VT measurements and line direction, then trace the phase distance zones and breaker trip matrix. 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 generator protection feature table). 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 CT and VT measurements and line direction.
- Trace the phase distance zones and breaker trip matrix.
Information to show or reference
- Label the phase CT and VT measurements and line direction.
- Cross-reference the phase distance zones and breaker trip matrix.
- Retain the complete suffix, selected device tag and manufacturer manual revision.
A distinction that matters
A phase distance element uses phase-fault loops; ground distance 21G includes the earth-return circuit treatment.
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.
Generator protection feature and function comparison
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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