{"schemaVersion":1,"slug":"21g-ground-distance-protection","name":"Ground distance protection","kind":"function","abbreviation":"21G","aliases":["earth distance","ground impedance","ANSI 21G","IEEE 21G"],"category":"measurement-protection","drawingTypes":["SLD","Schematic"],"referenceFamilies":["IEEE / ANSI","Manufacturer"],"summary":"Evaluates a distance characteristic for a phase-to-earth fault loop.","description":["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."],"readingNotes":["Identify the phase and residual current references, VT circuit and protected line.","Trace the ground distance zones and earth-loop compensation reference."],"drawingChecklist":["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."],"distinction":"Ground distance includes the ground-loop measurement treatment; it is not simply phase distance with a different alarm label.","facts":[{"label":"Function designation","value":"21G"},{"label":"Base function","value":"21 — Distance protection"},{"label":"Published mapping","value":"SEL line protection documentation"},{"label":"Suffix scope","value":"Application or manufacturer specific; check the complete drawing legend and selected device manual."}],"references":[{"sourceId":"pub-function-sel-product-catalog","relevance":"Explicit public manufacturer mapping of 21P to phase distance and 21G to ground distance in the protection feature tables."},{"sourceId":"pub-function-sel-distance","relevance":"Public primary-source function or application mapping used to identify this designation; wording and drafting notes are original."},{"sourceId":"ieee-functions","relevance":"Device-number and suffix convention. This page is not a reproduction of the full licensed standard."}],"related":["21-distance-protection","current-transformer"],"artwork":"pub-function-box","publishedOn":"2026-10-13","updatedOn":"2026-10-13","provenance":"independent-public-research","url":"https://eloragrid.ai/protection-functions/21g-ground-distance-protection","illustration":{"url":"https://eloragrid.ai/library/illustrations/21g-ground-distance-protection.svg","scope":"Original educational concept; not an official standard graphic or product footprint","license":"https://creativecommons.org/licenses/by/4.0/"},"sources":[{"id":"pub-function-sel-product-catalog","title":"SEL 2022 Product and Solution Guide: published protection function tables","publisher":"Schweitzer Engineering Laboratories","url":"https://selinc.com/api/download/136012","type":"manufacturer","scope":"Public historical product guide documenting 21P phase distance and 21G ground distance mappings among other line-protection functions. Referenced for terminology, not current product availability or a product recommendation.","checkedOn":"2026-10-13","reuse":"link-only","relevance":"Explicit public manufacturer mapping of 21P to phase distance and 21G to ground distance in the protection feature tables."},{"id":"pub-function-sel-distance","title":"SEL-321 phase and ground distance relay documentation","publisher":"Schweitzer Engineering Laboratories","url":"https://selinc.com/products/321/docs/","type":"manufacturer","scope":"Manufacturer documentation landing page for phase and ground distance protection. The legacy product is referenced to explain the measurement roles, not to recommend it for a new project.","checkedOn":"2026-10-13","reuse":"link-only","relevance":"Public primary-source function or application mapping used to identify this designation; wording and drafting notes are original."},{"id":"ieee-functions","title":"IEEE C37.2-2022: power-system device function numbers","publisher":"IEEE","url":"https://ieeexplore.ieee.org/document/9984140","type":"standard","scope":"Device function numbers, acronyms and contact designations. The full publication may require access through IEEE.","checkedOn":"2026-10-13","reuse":"link-only","relevance":"Device-number and suffix convention. This page is not a reproduction of the full licensed standard."}]}