Open Delta Transformer Connection Diagram for Three-Phase Systems

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.

Frequently Asked Questions - open-delta Transformer Connection:

What is an Open Delta transformer connection?

A configuration using two transformers to supply three-phase load instead of three.

When is it used?

For reduced load requirements, rural distribution, or temporary installations.

What is another name for it?

V-V connection.

How much capacity does it provide?

Approximately 86.6% of full delta transformer capacity.

Can it supply full three-phase load?

No, only partial load; suitable for light or emergency use.

Is earthing required?

Yes, for safety and proper operation.

How to check voltages?

Measure line-to-line and line-to-neutral voltages on the secondary side.

How to maintain phase sequence?

Proper phasor alignment is required on primary delta connection.

Can it be used for motors?

Yes, if motor load is within capacity limits.

Why use open delta instead of full delta?

To save one transformer and reduce cost when full capacity is not needed.

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