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# Delta-wye transformer

A delta-wye (Δ-Y) transformer is a transformer that converts three-phase electric power without a neutral wire into 3-phase power with a neutral wire. It can be a single three-phase transformer, or built from three independent single-phase units. The term Delta-Wye transformer is used in North America, and Delta-Star system in Europe.

Delta Wye Transformer

Delta-wye transformers are common in commercial, industrial, and high-density residential locations, to supply three-phase distribution systems.

An example would be a distribution transformer with a delta primary, running on three 11kV phases with no neutral or earth required, and a star (or wye) secondary providing a 3-phase supply at 400 V, with the domestic voltage of 230 available between each phase and an earthed neutral point.

## Output voltages

The line-to-neutral voltage is the voltage between any phase and neutral. The line-to-line voltage is the voltage between any two phases, and is equal to the phase to neutral voltage x $\sqrt{3}$ in balanced steady-state operation.

Phase-to-neutral voltage Phase-to-phase voltage (rounded)
120 208
127 220
220 380
230 400
240 415
250 433
277 480
347 600

The closed circuit on the delta side provides some benefits. Voltages on the secondaries have improved balance. Also it cancels third (or ninth et cetera) harmonics since these are not supported on the three-wire system.

## Phasing

Delta-wye transformers introduce a 30 degree phase shift. Thus they cannot be paralleled with wye-wye (or delta-delta) transformers; they can be paralleled with other delta-wye (or wye-delta with some attention) transformers.

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