{"schemaVersion":1,"slug":"open-delta-voltage-transformer-connection","name":"Open-delta voltage transformer connection","kind":"symbol","abbreviation":"VT","aliases":["V-V VT connection","two-VT open delta"],"category":"measurement-protection","drawingTypes":["SLD","Schematic"],"referenceFamilies":["IEC","IEEE / ANSI","Manufacturer"],"summary":"Two phase-to-phase VTs connected in V to provide all three line voltages without a neutral reference.","description":["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."],"readingNotes":["Identify the common phase shared by both VTs.","Check that no connected device needs phase-to-neutral voltage."],"drawingChecklist":["Show both VTs and common phase","State ratios","Reference secondary earthing point"],"distinction":"An open-delta connection uses two phase-to-phase VTs; a broken-delta winding uses three earthed VTs for residual voltage.","facts":[{"label":"VT count","value":"Two double-pole VTs"},{"label":"Not available","value":"Phase-to-neutral and residual voltage"},{"label":"Preview","value":"Independent educational concept; consult the applicable standard and project legend for the exact graphic"}],"references":[{"sourceId":"instrument-transformers","relevance":"Public manufacturer overview of indoor current and voltage instrument transformers."},{"sourceId":"autodesk-transformers","relevance":"Public potential-transformer symbol family used for context."}],"related":["voltage-transformer","voltage-transformer-with-residual-winding","ansi-voltage-transformer"],"artwork":"s28-open-delta-voltage-transformer-connection","publishedOn":"2026-10-28","updatedOn":"2026-10-28","provenance":"independent-public-research","plainEnglish":{"title":"What does Open-delta voltage transformer connection mean?","introduction":"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.","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.","drawings":"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.","terms":[{"name":"Winding","meaning":"A coil of conductor inside an electrical machine or transformer."},{"name":"Normally open / normally closed","meaning":"The contact state in the normal condition defined for the drawing."},{"name":"Coil","meaning":"A wound conductor that can produce a magnetic field when energised."}],"diagram":"flow","steps":["Identify the device and form","Read the connections and state","Check the equipment reference"],"caption":"A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram.","sources":[{"label":"Indoor current and voltage transformers","url":"https://www.abb.com/gb/en/areas/electrification/medium-voltage/grid-components/core-components/indoor-instrument-transformers"},{"label":"Power, potential and autotransformer symbols","url":"https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-C1FE1690-DBF4-4F69-85C4-28E41F0A6392.htm"}],"detail":"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.","profileId":"reviewed-symbol-20261028"},"url":"https://eloragrid.ai/symbols/open-delta-voltage-transformer-connection","illustration":{"url":"https://eloragrid.ai/tools/electrical-library/illustrations/open-delta-voltage-transformer-connection.svg","scope":"Original educational concept; not an official standard graphic or product footprint","license":"https://creativecommons.org/licenses/by/4.0/"},"sources":[{"id":"instrument-transformers","title":"Indoor current and voltage transformers","publisher":"ABB","url":"https://www.abb.com/gb/en/areas/electrification/medium-voltage/grid-components/core-components/indoor-instrument-transformers","type":"manufacturer","scope":"Public current- and voltage-transformer product families. Ratings, terminals and dimensions depend on the model.","checkedOn":"2026-10-13","reuse":"link-only","relevance":"Public manufacturer overview of indoor current and voltage instrument transformers."},{"id":"autodesk-transformers","title":"Power, potential and autotransformer symbols","publisher":"Autodesk","url":"https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-C1FE1690-DBF4-4F69-85C4-28E41F0A6392.htm","type":"cad-reference","scope":"Power transformers, voltage transformers, winding counts, screens and autotransformers.","checkedOn":"2026-10-13","reuse":"link-only","relevance":"Public potential-transformer symbol family used for context."}]}