50
Instantaneous overcurrent
An overcurrent function without an intentional operating time delay in its instantaneous application.
Protection functions
Protection functions · 50Q
Instantaneous negative-sequence overcurrent
Supervises negative-sequence current for an instantaneous overcurrent element.
SLD / Schematic · 50Q
What it represents
Supervises negative-sequence current for an instantaneous overcurrent element.
The drafting record should connect this function to the three phase-current inputs and calculated negative-sequence quantity, then trace the negative-sequence element and selected 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 generator protection feature 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 three phase-current inputs and calculated negative-sequence quantity.
- Trace the negative-sequence element and selected trip matrix.
Information to show or reference
- Label the three phase-current inputs and calculated negative-sequence quantity.
- Cross-reference the negative-sequence element and selected trip matrix.
- Retain the complete suffix, selected device tag and manufacturer manual revision.
A distinction that matters
Negative-sequence current is a derived unbalance quantity; it is not a fourth physical CT channel merely because a separate function appears on the SLD.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
Generator protection feature and function comparison
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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