87
Differential protection
A function comparing documented electrical quantities across a protection zone.
Protection functions
Protection functions · 87T
Transformer differential protection
Compares currents associated with a transformer protection zone using the selected relay's differential method.
SLD / Schematic · 87T
What it represents
Compares currents associated with a transformer protection zone using the selected relay's differential method.
The drafting record should connect this function to the transformer winding CT circuits, polarity and ratio references, then trace the transformer differential zone and breaker 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 (ABB Relion 620 function mapping). 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 transformer winding CT circuits, polarity and ratio references.
- Trace the transformer differential zone and breaker trip matrix.
Information to show or reference
- Label the transformer winding CT circuits, polarity and ratio references.
- Cross-reference the transformer differential zone and breaker trip matrix.
- Retain the complete suffix, selected device tag and manufacturer manual revision.
A distinction that matters
Transformer differential needs a defined zone and winding compensation; it differs from restricted earth-fault protection limited to one earthed winding.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
Relion 620 series: published protection function and designation mappings
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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