87
Differential protection
A function comparing documented electrical quantities across a protection zone.
Protection functions
Protection functions · 87B
Busbar differential protection
Compares currents at the boundaries of a busbar protection zone.
SLD / Schematic · 87B
What it represents
Compares currents at the boundaries of a busbar protection zone.
The drafting record should connect this function to the CTs bounding the bus zone and any zone-selection status contacts, then trace the bus differential trip matrix and included breakers. 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 CTs bounding the bus zone and any zone-selection status contacts.
- Trace the bus differential trip matrix and included breakers.
Information to show or reference
- Label the CTs bounding the bus zone and any zone-selection status contacts.
- Cross-reference the bus differential trip matrix and included breakers.
- Retain the complete suffix, selected device tag and manufacturer manual revision.
A distinction that matters
87B commonly identifies bus differential, but ABB also uses 87B for a phase-B high-impedance element; the application legend resolves the meaning.
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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