# Open-delta voltage transformer connection

Canonical URL: https://eloragrid.ai/symbols/open-delta-voltage-transformer-connection
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: VT
Drawing use: SLD, Schematic
Reference families: IEC, IEEE / ANSI, Manufacturer

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.

### Terms

- 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.

Concept diagram: Identify the device and form → Read the connections and state → Check the equipment reference
A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram.

- [Indoor current and voltage transformers](https://www.abb.com/gb/en/areas/electrification/medium-voltage/grid-components/core-components/indoor-instrument-transformers)
- [Power, potential and autotransformer symbols](https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-C1FE1690-DBF4-4F69-85C4-28E41F0A6392.htm)


## 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

## Important distinction

An open-delta connection uses two phase-to-phase VTs; a broken-delta winding uses three earthed VTs for residual voltage.

## Facts

- VT count: Two double-pole VTs
- Not available: Phase-to-neutral and residual voltage
- Preview: Independent educational concept; consult the applicable standard and project legend for the exact graphic

## Public references

- [Indoor current and voltage transformers](https://www.abb.com/gb/en/areas/electrification/medium-voltage/grid-components/core-components/indoor-instrument-transformers) — ABB. Public manufacturer overview of indoor current and voltage instrument transformers.
- [Power, potential and autotransformer symbols](https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-C1FE1690-DBF4-4F69-85C4-28E41F0A6392.htm) — Autodesk. Public potential-transformer symbol family used for context.

## Graphic scope

Independent original educational concept illustration by Elora Grid. Not a certified standards graphic or manufacturer footprint. Unitless; not to scale. Original artwork licence: https://creativecommons.org/licenses/by/4.0/. Publisher material is linked only.