{"schemaVersion":1,"slug":"51q-time-negative-sequence-overcurrent","name":"Time negative-sequence overcurrent","kind":"function","abbreviation":"51Q","aliases":["negative sequence IDMT","I2 time overcurrent","ANSI 51Q","IEEE 51Q"],"category":"measurement-protection","drawingTypes":["SLD","Schematic"],"referenceFamilies":["IEEE / ANSI","Manufacturer"],"summary":"Supervises negative-sequence current using a time-dependent operating criterion.","description":["Supervises negative-sequence current using a time-dependent operating criterion.","The drafting record should connect this function to the three phase CT measurements used to derive negative-sequence current, then trace the unbalance-sensitive timed trip and coordination 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 (Eaton ETR family). Suffixes are not universal equivalences across products, and this reference supplies neither a protection setting nor certification of the selected scheme."],"readingNotes":["Identify the three phase CT measurements used to derive negative-sequence current.","Trace the unbalance-sensitive timed trip and coordination reference."],"drawingChecklist":["Label the three phase CT measurements used to derive negative-sequence current.","Cross-reference the unbalance-sensitive timed trip and coordination reference.","Retain the complete suffix, selected device tag and manufacturer manual revision."],"distinction":"51Q is a negative-sequence time-overcurrent element; generator thermal unbalance protection may use a separate machine-damage model.","facts":[{"label":"Function designation","value":"51Q"},{"label":"Base function","value":"51 — Time overcurrent"},{"label":"Published mapping","value":"Eaton ETR family"},{"label":"Suffix scope","value":"Application or manufacturer specific; check the complete drawing legend and selected device manual."}],"references":[{"sourceId":"pub-function-eaton-transformer","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":["51-time-overcurrent","current-transformer"],"artwork":"pub-function-box","publishedOn":"2026-10-13","updatedOn":"2026-10-13","provenance":"independent-public-research","url":"https://eloragrid.ai/protection-functions/51q-time-negative-sequence-overcurrent","illustration":{"url":"https://eloragrid.ai/library/illustrations/51q-time-negative-sequence-overcurrent.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-transformer","title":"ETR-4000 and ETR-5000 transformer protection function tables","publisher":"Eaton","url":"https://www.eaton.com/us/en-us/catalog/electrical-circuit-protection/transformer-relays.html","type":"manufacturer","scope":"Public transformer-relay mappings including restrained/unrestrained differential, restricted ground differential, main and auxiliary voltage inputs, and measured/calculated earth-current inputs.","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."}]}