# Negative-sequence differential protection

Canonical URL: https://eloragrid.ai/protection-functions/87q-negative-sequence-differential-protection
Publisher: Elora Grid
Updated: 2026-10-13
Lookup label: 87Q
Drawing use: SLD, Schematic
Reference families: IEEE / ANSI, Manufacturer

Compares negative-sequence current information across a differential protection zone.

## What it represents

Compares negative-sequence current information across a differential protection zone.
The drafting record should connect this function to the zone-boundary phase-current measurements and sequence compensation reference, then trace the negative-sequence differential element and associated trip 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 (SEL public device-number table). Suffixes are not universal equivalences across products, and this reference supplies neither a protection setting nor certification of the selected scheme.

## How to read it

- Identify the zone-boundary phase-current measurements and sequence compensation reference.
- Trace the negative-sequence differential element and associated trip output.

## Information to show or reference

- Label the zone-boundary phase-current measurements and sequence compensation reference.
- Cross-reference the negative-sequence differential element and associated trip output.
- Retain the complete suffix, selected device tag and manufacturer manual revision.

## Important distinction

Sequence differential 87Q is not the same as local negative-sequence overcurrent 51Q; it compares quantities across a zone.

## Facts

- Function designation: 87Q
- Base function: 87 — Differential protection
- Published mapping: SEL public device-number table
- Suffix scope: Application or manufacturer specific; check the complete drawing legend and selected device manual.

## Public references

- [ANSI device-number and suffix reference table](https://selinc.com/pt/products/tables/ansi/) — Schweitzer Engineering Laboratories. Public primary-source function or application mapping used to identify this designation; wording and drafting notes are original.
- [IEEE C37.2-2022: power-system device function numbers](https://ieeexplore.ieee.org/document/9984140) — IEEE. Device-number and suffix convention. This page is not a reproduction of the full licensed standard.

## Graphic scope

Independent original educational concept illustration by Elora Grid. Not a certified standards graphic or manufacturer footprint. Unitless; not to scale. Original artwork licence: https://creativecommons.org/licenses/by/4.0/. Publisher material is linked only.