87
Differential protection
A function comparing documented electrical quantities across a protection zone.
Protection functions
Protection functions · 87N
Neutral differential protection
Identifies a differential scheme involving neutral or residual-current quantities as defined by the equipment documentation.
SLD / Schematic · 87N
What it represents
Identifies a differential scheme involving neutral or residual-current quantities as defined by the equipment documentation.
The drafting record should connect this function to the neutral and phase/residual CT circuits and protected winding boundary, then trace the neutral differential operating element and earth-fault 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 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 neutral and phase/residual CT circuits and protected winding boundary.
- Trace the neutral differential operating element and earth-fault trip matrix.
Information to show or reference
- Label the neutral and phase/residual CT circuits and protected winding boundary.
- Cross-reference the neutral differential operating element and earth-fault trip matrix.
- Retain the complete suffix, selected device tag and manufacturer manual revision.
A distinction that matters
The N suffix does not establish whether the scheme is high- or low-impedance restricted earth fault; record the actual scheme.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
ANSI device-number and suffix reference table
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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