# Admittance-based earth-fault protection

Canonical URL: https://eloragrid.ai/protection-functions/21yn-admittance-based-earth-fault-protection
Publisher: Elora Grid
Updated: 2026-10-13
Lookup label: 21YN
Drawing use: SLD, Schematic
Reference families: IEEE / ANSI, Manufacturer

Uses earth-fault voltage and current relationships to assess an admittance-based directional criterion.

## What it represents

Uses earth-fault voltage and current relationships to assess an admittance-based directional criterion.
The drafting record should connect this function to the residual voltage and residual current measurements and neutral-earthing method, then trace the earth-fault operating element and selected feeder trip. 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 (ABB Relion 620 function mapping). 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 residual voltage and residual current measurements and neutral-earthing method.
- Trace the earth-fault operating element and selected feeder trip.

## Information to show or reference

- Label the residual voltage and residual current measurements and neutral-earthing method.
- Cross-reference the earth-fault operating element and selected feeder trip.
- Retain the complete suffix, selected device tag and manufacturer manual revision.

## Important distinction

ABB documents 21YN for EFPADM; this admittance earth-fault function is distinct from a generic line-distance zone.

## Facts

- Function designation: 21YN
- Base function: 21 — Distance protection
- Published mapping: ABB Relion 620 function mapping
- Suffix scope: Application or manufacturer specific; check the complete drawing legend and selected device manual.

## Public references

- [Relion 620 series: published protection function and designation mappings](https://techdoc.relays.protection-control.abb/r/620-series-IEC-60870-5-103-Point-List-Manual/2.0-FP1-IEC/en-US/Functions-codes-and-symbols) — ABB. 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](https://ieeexplore.ieee.org/document/9984140) — IEEE. Device-number and suffix convention. This page is not a reproduction of the full licensed standard.

## 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.