{"schemaVersion":1,"slug":"27q-reactive-power-undervoltage-protection","name":"Reactive-power undervoltage protection","kind":"function","abbreviation":"27Q","aliases":["reactive power undervoltage","Q U protection","ANSI 27Q","IEEE 27Q"],"category":"measurement-protection","drawingTypes":["SLD","Schematic"],"referenceFamilies":["IEEE / ANSI","Manufacturer"],"summary":"Combines a reactive-power criterion with undervoltage supervision in the cited interconnection application.","description":["Combines a reactive-power criterion with undervoltage supervision in the cited interconnection application.","The drafting record should connect this function to the voltage and current inputs and defined reactive-power direction, then trace the combined reactive-power and undervoltage operating logic. 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 voltage and current inputs and defined reactive-power direction.","Trace the combined reactive-power and undervoltage operating logic."],"drawingChecklist":["Label the voltage and current inputs and defined reactive-power direction.","Cross-reference the combined reactive-power and undervoltage operating logic.","Retain the complete suffix, selected device tag and manufacturer manual revision."],"distinction":"27Q is an Eaton application designation; ABB separately labels a related function 32Q,27, so retain the device-specific legend.","facts":[{"label":"Function designation","value":"27Q"},{"label":"Base function","value":"27 — Undervoltage"},{"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":["27-undervoltage","voltage-transformer"],"artwork":"pub-function-box","publishedOn":"2026-10-13","updatedOn":"2026-10-13","provenance":"independent-public-research","url":"https://eloragrid.ai/protection-functions/27q-reactive-power-undervoltage-protection","illustration":{"url":"https://eloragrid.ai/library/illustrations/27q-reactive-power-undervoltage-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-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."}]}