{"schemaVersion":1,"slug":"87-differential","name":"Differential protection","kind":"function","abbreviation":"87","aliases":["differential relay","87T","87B","87G","differential protection relay"],"category":"measurement-protection","drawingTypes":["SLD","Schematic"],"referenceFamilies":["IEEE / ANSI"],"summary":"A function comparing documented electrical quantities across a protection zone.","description":["Differential protection compares quantities associated with the boundaries of a protection zone according to the selected implementation. Equipment and application suffixes can distinguish transformer, busbar, line or other arrangements. The base number alone does not define the zone or measurements.","On a power drawing, keep this function reference connected to the selected equipment and its complete designation. A multifunction relay can implement several numbered functions. This entry explains the reference; it supplies no settings or commissioning procedure."],"readingNotes":["Identify the protected zone and each measurement boundary.","Read CT associations, polarity and any device-specific compensation from the protection documentation."],"drawingChecklist":["Identify the protected equipment or zone.","Reference measurement boundaries.","Link the relay application and trip destinations."],"distinction":"Transformer differential, busbar differential and other differential applications are not interchangeable merely because they share the base number 87.","facts":[{"label":"ANSI / IEEE function number","value":"87"},{"label":"Equipment implementation","value":"Consult the selected device manual"},{"label":"Suffix interpretation","value":"Application and manufacturer documentation"}],"references":[{"sourceId":"device-numbers","relevance":"Public manufacturer table used to check the base function-number name."},{"sourceId":"ieee-functions","relevance":"Normative publication reference for the device-function convention."},{"sourceId":"abb-functions","relevance":"Public examples of manufacturer-specific function names and suffixes."}],"related":["current-transformer","power-transformer","busbar"],"artwork":"function","publishedOn":"2026-10-13","updatedOn":"2026-10-13","provenance":"independent-public-research","url":"https://eloragrid.ai/protection-functions/87-differential","illustration":{"url":"https://eloragrid.ai/library/illustrations/87-differential.svg","scope":"Original educational concept; not an official standard graphic or product footprint","license":"https://creativecommons.org/licenses/by/4.0/"},"sources":[{"id":"device-numbers","title":"Public reference table of ANSI device-function numbers","publisher":"Schneider Electric","url":"https://www.se.com/es/es/faqs/FA34639/","type":"manufacturer","scope":"Spanish-language public reference table. Used to check device-number names; no claim that every function is implemented in every device.","checkedOn":"2026-10-13","reuse":"link-only","relevance":"Public manufacturer table used to check the base function-number name."},{"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":"Normative publication reference for the device-function convention."},{"id":"abb-functions","title":"Relion 620: functions, codes and symbols","publisher":"ABB","url":"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","type":"manufacturer","scope":"Published product mappings between function names, IEC 61850 identifiers, IEC mnemonics and ANSI designations. These are product examples, not universal equivalences.","checkedOn":"2026-10-13","reuse":"link-only","relevance":"Public examples of manufacturer-specific function names and suffixes."}]}