Three-Phase Transformer Connections: An Overview of Y-Y, Y-D, D-Y, and D-D Configurations, Slides of Electrical Engineering

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Electrical

Machines

3 ϕ Transformers

Nuha Nadhiroh

• Transformer Polarity
• Three phase Transformer Connections

Overview

3 ϕ Transformer Connections

• Transformers for three-phase circuits can be constructed in one of two ways:
• One approach is simply to take three single-phase transformers and connect them in a three-phase bank.
• An alternative approach is to make a three-phase transformer consisting of three sets of windings wrapped on a common core. Single Three-legged Transformer 3 independent Transformer

3 ϕ Transformer Connections

• The primaries and secondaries of any three-phase transformer can be independently connected in either a wye (Y) or a delta (D):
• Y-Y
• Y-D
• D-Y
• D-D

• The Y-D connection has no problem with third-harmonic components in its voltages, since they are consumed in a circulating current on the D side.
• This connection is also more stable with respect to unbalanced loads, since the D partially redistributes any imbalance that occurs. Y-D Connections

• This connection has the same advantages and the same phase shift as the Y-D transformer.
• The connection makes the secondary voltage lag the primary voltage by 30° D-Y Connections

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