78
Phase-angle or out-of-step protection
Supervises the angular relationship or loss of synchronism of an electrical system or machine.
Protection functions
Protection functions · 78VS
Voltage vector-shift protection
Supervises an abrupt change in the measured voltage phase angle using the selected relay's vector-shift method.
SLD / Schematic · 78VS
What it represents
Supervises an abrupt change in the measured voltage phase angle using the selected relay's vector-shift method.
The drafting record should connect this function to the measured voltage inputs and interconnection point, then trace the vector-shift operating output and interconnection protection logic. 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 measured voltage inputs and interconnection point.
- Trace the vector-shift operating output and interconnection protection logic.
Information to show or reference
- Label the measured voltage inputs and interconnection point.
- Cross-reference the vector-shift operating output and interconnection protection logic.
- Retain the complete suffix, selected device tag and manufacturer manual revision.
A distinction that matters
Vector shift 78VS/78V is a product-mapped function and differs from the complete out-of-step or pole-slip application of base 78.
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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