open-delta Transformer Connection
Learn how to wire an Open Delta transformer connection for three-phase systems using two transformers to supply three-phase loads efficiently.
reduced transformer connection
The transformer circuit of open delta enables three-phase power to be fed with only two transformers. It is economical when there is a low load need and an emergency or remote distribution system.
open delta distribution diagram
The connection of an open Delta transformer is employed to supply three-phase loads with two transformers instead of three, also known as the V connection. The given setup proves to be cost-effective in case a full three-phase capacity is not needed. Two transformers have their primary windings connected in delta, and the secondary windings are connected in delta with a missing phase to provide three three-phase loads. Open Delta transformers can deliver about 86.6 percent of the capacity of a full delta connection, although this is enough in a light industrial or emergency application. There should be proper voltage, neutral, and earth connections, particularly to facilitate safe functioning. The testing includes checking line-to-line and line-to-neutral voltage with a proper three-phase supply. They are commonly applied in open distribution in industry as well as in rural electrification and temporary installations where full transformer sets are nonexistent or uneconomical.
Work & Installation (Input → Output Summary)
- Connect theprimary windings of the two transformers in deltaconfiguration.
- Connect thesecondary windings to supply the three-phase load in open delta.
- Ensure properline voltages, neutral, and earth connections.
- Checkphasor alignment to maintain correct phase sequence.
- Apply supply and measure line-to-line voltages to verify proper three-phase output.
- Connect loads according to the available three-phase supply.
Testing & Final Adjustments
- Verify correct primary delta connection.
- Check secondary open delta connections for all load phases.
- Measure line-to-line and line-to-neutral voltages.
- Confirm correct phase sequence using a phase sequence meter.
- Inspect transformer insulation, earth, and neutral connections.
- Ensure no phase is overloaded beyond rated capacity (~86.6%).
- Test with a light load first before full load application.
- Monitor for abnormal heating or voltage imbalance.
- Document connections and voltage readings for future reference.
- Label transformer terminals for maintenance and safety.
