In this example case the transformer current vectors and the transformer connection looks like in the
following gure.
Figure. 5.4.18. - 75. Yd1 transformer internal connection in principle.
In modern relays these standard vector groups (wye, delta, lead or lag) are de ned by a setting
selection and there is no need for interposing transformers. If the transformer vector group is not
standard it should still be settable within the relay (in case of zigzag transformers).
In this case in differential relay the differential function applies following translation to delta side
currents (note that the correction is not only to the angles but also to the amplitudes since the per
unitized delta side has relation amplitude difference to star connected side)
AQ-T257
Instruction manual
Version: 2.00
147
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