VT / PT
Voltage transformer
A transformer providing a voltage signal for metering or protection.
SLD / Schematic
Symbols · VT
Open-delta voltage transformer connection
Two phase-to-phase VTs connected in V to provide all three line voltages without a neutral reference.
In plain English
What does Open-delta voltage transformer connection mean?
The open-delta or V-V connection uses two double-pole VTs connected between phases, sharing one phase as a common point. It gives all three line-to-line secondary voltages at lower cost than three VTs and is common in MV metering and switchgear where neutral voltages are not needed.
A simple example
Because there is no neutral reference, phase-to-neutral voltages and zero-sequence voltage cannot be measured. Earth-fault directional elements or meters needing phase-to-neutral inputs therefore cannot be fed from this connection, which the reader must check against the relay requirements.
What the drawings help you do
Identify the common phase shared by both VTs. Check that no connected device needs phase-to-neutral voltage. An open-delta connection uses two phase-to-phase VTs; a broken-delta winding uses three earthed VTs for residual voltage.
This particular reference
Two phase-to-phase VTs connected in V to provide all three line voltages without a neutral reference. An open-delta connection uses two phase-to-phase VTs; a broken-delta winding uses three earthed VTs for residual voltage.
- Winding
- A coil of conductor inside an electrical machine or transformer.
- Normally open / normally closed
- The contact state in the normal condition defined for the drawing.
- Coil
- A wound conductor that can produce a magnetic field when energised.
Read the source: Indoor current and voltage transformers · Power, potential and autotransformer symbols
SLD / Schematic · VT
What it represents
The open-delta or V-V connection uses two double-pole VTs connected between phases, sharing one phase as a common point. It gives all three line-to-line secondary voltages at lower cost than three VTs and is common in MV metering and switchgear where neutral voltages are not needed.
Because there is no neutral reference, phase-to-neutral voltages and zero-sequence voltage cannot be measured. Earth-fault directional elements or meters needing phase-to-neutral inputs therefore cannot be fed from this connection, which the reader must check against the relay requirements.
How to read it
- Identify the common phase shared by both VTs.
- Check that no connected device needs phase-to-neutral voltage.
Information to show or reference
- Show both VTs and common phase
- State ratios
- Reference secondary earthing point
A distinction that matters
An open-delta connection uses two phase-to-phase VTs; a broken-delta winding uses three earthed VTs for residual voltage.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
Indoor current and voltage transformers
Public manufacturer overview of indoor current and voltage instrument transformers.
Power, potential and autotransformer symbols
Public potential-transformer symbol family used for context.
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.
Explore related references
VT
Voltage transformer set with broken-delta residual winding
Three single-phase VTs whose residual windings are connected in broken delta to produce the zero-sequence voltage.
SLD / Schematic
VT / PT
ANSI/IEEE voltage transformer symbol
IEEE-oriented graphical reference for voltage transformer, with public vendor evidence and drawing-reading notes.
IEEE / ANSI
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