81
Frequency protection
A function responding to a documented frequency condition.
Protection functions
Protection functions · 81O
Overfrequency protection
Supervises frequency above the defined operating criterion.
SLD / Schematic · 81O
What it represents
Supervises frequency above the defined operating criterion.
The drafting record should connect this function to the frequency measurement source and enabled overfrequency stage, then trace the generator or interconnection overfrequency 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 (Eaton E-Series 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 frequency measurement source and enabled overfrequency stage.
- Trace the generator or interconnection overfrequency output.
Information to show or reference
- Label the frequency measurement source and enabled overfrequency stage.
- Cross-reference the generator or interconnection overfrequency output.
- Retain the complete suffix, selected device tag and manufacturer manual revision.
A distinction that matters
The suffix O is the letter O for overfrequency; use the complete label to avoid confusion with a zero in search or drawing text.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
E-Series protective relays: public family comparison brochure
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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