VT / PT
Voltage transformer
A transformer providing a voltage signal for metering or protection.
SLD / Schematic
Protection functions · 25
Synchronism check
Checks documented synchronising conditions before a permitted connection.
SLD / Schematic · 25
What it represents
A synchronism-check function supervises the conditions for connecting electrical sources or system sections. It is associated with the measured quantities and operating logic specified for the selected protection or control device.
On a power drawing, keep this function reference connected to the selected equipment and its complete designation. A multifunction relay can implement several numbered functions. This entry explains the reference; it supplies no settings or commissioning procedure.
How to read it
- Identify the voltage measurement inputs used by the function.
- Read the closing-permission relationship in the documented control scheme.
Information to show or reference
- Reference measured source or bus voltages.
- Identify the supervised closing device.
- Link the control and protection documentation.
A distinction that matters
Synchronism checking is a permissive function; a generic 25 label is not a complete synchronising controller or operating sequence.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
Public reference table of ANSI device-function numbers
Public manufacturer table used to check the base function-number name.
IEEE C37.2-2022: power-system device function numbers
Normative publication reference for the device-function convention.
Relion 620: functions, codes and symbols
Public examples of manufacturer-specific function names and suffixes.
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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