{"schemaVersion":1,"slug":"81o-overfrequency-protection","name":"Overfrequency protection","kind":"function","abbreviation":"81O","aliases":["high frequency","over frequency","OF protection","ANSI 81O","IEEE 81O"],"category":"measurement-protection","drawingTypes":["SLD","Schematic"],"referenceFamilies":["IEEE / ANSI","Manufacturer"],"summary":"Supervises frequency above the defined operating criterion.","description":["Supervises frequency above the defined operating criterion.","The drafting record should connect this function to the frequency measurement source and enabled overfrequency stage, then trace the generator or interconnection overfrequency output. 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 (Eaton E-Series function mapping). Suffixes are not universal equivalences across products, and this reference supplies neither a protection setting nor certification of the selected scheme."],"readingNotes":["Identify the frequency measurement source and enabled overfrequency stage.","Trace the generator or interconnection overfrequency output."],"drawingChecklist":["Label the frequency measurement source and enabled overfrequency stage.","Cross-reference the generator or interconnection overfrequency output.","Retain the complete suffix, selected device tag and manufacturer manual revision."],"distinction":"The suffix O is the letter O for overfrequency; use the complete label to avoid confusion with a zero in search or drawing text.","facts":[{"label":"Function designation","value":"81O"},{"label":"Base function","value":"81 — Frequency protection"},{"label":"Published mapping","value":"Eaton E-Series function mapping"},{"label":"Suffix scope","value":"Application or manufacturer specific; check the complete drawing legend and selected device manual."}],"references":[{"sourceId":"pub-function-eaton-brochure","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":["81-frequency","voltage-transformer"],"artwork":"pub-function-box","publishedOn":"2026-10-13","updatedOn":"2026-10-13","provenance":"independent-public-research","url":"https://eloragrid.ai/protection-functions/81o-overfrequency-protection","illustration":{"url":"https://eloragrid.ai/library/illustrations/81o-overfrequency-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-eaton-brochure","title":"E-Series protective relays: public family comparison brochure","publisher":"Eaton","url":"https://www.eaton.com/content/dam/eaton/products/electrical-circuit-protection/protective-relays-and-predictive-devices/e-series-protective-relays-br026001en.pdf","type":"manufacturer","scope":"Public function-name and suffix mappings across feeder, motor, transformer and generator relays. Linked as documentation only; no illustrations or product drawings are copied.","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."}]}