87
Differential protection
A function comparing documented electrical quantities across a protection zone.
Protection functions
Protection functions · 87L
Line current differential protection
Compares current information from the terminals of a protected line using a communication-assisted differential scheme.
SLD / Schematic · 87L
What it represents
Compares current information from the terminals of a protected line using a communication-assisted differential scheme.
The drafting record should connect this function to the local and remote terminal CTs and protection communication links, then trace the line differential zone and terminal breaker trips. 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 line differential documentation). 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 local and remote terminal CTs and protection communication links.
- Trace the line differential zone and terminal breaker trips.
Information to show or reference
- Label the local and remote terminal CTs and protection communication links.
- Cross-reference the line differential zone and terminal breaker trips.
- Retain the complete suffix, selected device tag and manufacturer manual revision.
A distinction that matters
Line differential requires its measurement and communication arrangement; it is not a local distance zone or directional permissive alone.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
SEL-411L line differential protection overview
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
Device-number and suffix convention. This page is not a reproduction of the full licensed standard.
About this graphic
This illustration was authored independently by Elora Grid to explain the concept. It is not reproduced from a customer drawing, an official standard graphic or a manufacturer CAD file. Its correspondence to an exact IEC or IEEE symbol identifier has not been certified.
SVG and DXF downloads contain this original artwork. DXF uses unscaled drawing units; a GA envelope supplies no product dimensions, clearances or fabrication information. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.
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