VT / PT
Voltage transformer
A transformer providing a voltage signal for metering or protection.
SLD / Schematic
Protection functions · 91
Voltage directional relay
Uses a voltage relationship with a defined direction criterion in a specialist protection or control scheme.
SLD / Schematic · 91
What it represents
Uses a voltage relationship with a defined direction criterion in a specialist protection or control scheme.
In a drafting package, connect this reference to the compared voltage references and polarity convention. The associated drawing should trace the directional-voltage operating circuit; the number identifies the role and does not specify the terminal arrangement, ratings or operating settings.
This designation is useful when reading machine and legacy control drawings. Retain the documented function on an existing drawing and consult the original equipment manual before assigning it to a new design.
How to read it
- Identify the compared voltage references and polarity convention.
- Trace the directional-voltage operating circuit.
Information to show or reference
- Label the compared voltage references and polarity convention.
- Cross-reference the directional-voltage operating circuit.
- Identify the device tag, manual revision and logic drawing that define this implementation.
A distinction that matters
Directional voltage 91 is not equivalent to directional power 32 or ordinary overvoltage 59.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
ANSI device-number and suffix reference table
Public manufacturer number/name association. Drafting explanations are independently written.
IEEE C37.2-2022: power-system device function numbers
Normative device-number publication; exact edition wording and compliance require the 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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