27
Undervoltage
A function responding to voltage below its configured operating criteria.
Protection functions
Protection functions · 27A
Auxiliary-input undervoltage protection
Supervises low voltage using the auxiliary voltage input identified by the selected relay.
SLD / Schematic · 27A
What it represents
Supervises low voltage using the auxiliary voltage input identified by the selected relay.
The drafting record should connect this function to the auxiliary VT or voltage input and its phase assignment, then trace the auxiliary undervoltage output and any closing permission. 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 ETR family). 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 auxiliary VT or voltage input and its phase assignment.
- Trace the auxiliary undervoltage output and any closing permission.
Information to show or reference
- Label the auxiliary VT or voltage input and its phase assignment.
- Cross-reference the auxiliary undervoltage output and any closing permission.
- Retain the complete suffix, selected device tag and manufacturer manual revision.
A distinction that matters
In the cited Eaton family, A distinguishes the auxiliary measurement input; it is not a universal alarm-only suffix.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
ETR-4000 and ETR-5000 transformer protection function tables
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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