{"schemaVersion":1,"slug":"50q-instantaneous-negative-sequence-overcurrent","name":"Instantaneous negative-sequence overcurrent","kind":"function","abbreviation":"50Q","aliases":["negative sequence IOC","I2 instantaneous","ANSI 50Q","IEEE 50Q"],"category":"measurement-protection","drawingTypes":["SLD","Schematic"],"referenceFamilies":["IEEE / ANSI","Manufacturer"],"summary":"Supervises negative-sequence current for an instantaneous overcurrent element.","description":["Supervises negative-sequence current for an instantaneous overcurrent element.","The drafting record should connect this function to the three phase-current inputs and calculated negative-sequence quantity, then trace the negative-sequence element and selected trip matrix. 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 generator protection feature table). 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-current inputs and calculated negative-sequence quantity.","Trace the negative-sequence element and selected trip matrix."],"drawingChecklist":["Label the three phase-current inputs and calculated negative-sequence quantity.","Cross-reference the negative-sequence element and selected trip matrix.","Retain the complete suffix, selected device tag and manufacturer manual revision."],"distinction":"Negative-sequence current is a derived unbalance quantity; it is not a fourth physical CT channel merely because a separate function appears on the SLD.","facts":[{"label":"Function designation","value":"50Q"},{"label":"Base function","value":"50 — Instantaneous overcurrent"},{"label":"Published mapping","value":"SEL generator protection feature table"},{"label":"Suffix scope","value":"Application or manufacturer specific; check the complete drawing legend and selected device manual."}],"references":[{"sourceId":"pub-function-sel-generator","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":["50-instantaneous-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/50q-instantaneous-negative-sequence-overcurrent","illustration":{"url":"https://eloragrid.ai/library/illustrations/50q-instantaneous-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-sel-generator","title":"Generator protection feature and function comparison","publisher":"Schweitzer Engineering Laboratories","url":"https://selinc.com/products/comparisons/generator-protection/","type":"manufacturer","scope":"Public mappings for generator functions, including phase distance, field/stator ground, thermal RTD, sequence-current and vector-shift applications. Product availability depends on model/options; no settings are provided here.","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."}]}