Phase Matching Transformers

To phase match two three-phase delta/wye transformers fed from the same source, follow these steps

1. Identify the Primary and Secondary Terminals
Label the primary and secondary terminals of both transformers as follows: Primaries

A1, A2, A3

Secondaries

X1, X2, X3

2. Connect the Primaries Connect the primaries of both transformers in a delta configuration, as shown: A1 of transformer 1 to A1 of transformer 2 A2 of transformer 1 to A2 of transformer 2 A3 of transformer 1 to A3 of transformer 23. Power Up the Transformers Energize the primary windings with three-phase power.4. Check the Secondary Voltages Using a voltmeter, measure the line-to-line voltages between the secondary terminals of each transformer. The voltages should be balanced and in phase.5. Adjust Phase Relationships If the secondary voltages are not in phase, adjust the phase relationship by reversing the connections at one of the secondary terminals of transformer 2. Continue adjusting until the secondary voltages are balanced and in phase.

Relationship Between Primary and Secondary Phasing

The relationship between primary and secondary phasing in a delta/wye transformer is as follows: The phase sequence of the secondary is the same as the phase sequence of the primary. The phase angle of the secondary is shifted by 30° with respect to the primary.

Notes: If the transformers are being used in back-to-back connection, the secondary phasing must be 180° out of phase with the primary phasing. Refer to the manufacturer's instructions for specific phasing procedures.* It is essential to ensure proper phase matching to avoid circulation currents and potential damage to the transformers. Flag for review