Answer Posted / doug marshall

As I understand it, the convention is counterclockwise
rotation. Therefore DYn1 means that the secondary lags the
primary by 30 degrees (Subtractive Polarity). DYn11 means
that the secondary lags the primary by 330 degrees which is
the same as secondary leads the primary by 30 degrees
(Additive Polarity). Likewise, a DYn1 when operated as a
YnD1 (Step Up), the secondary or delta leads the primary Y
by 30 degrees. Therefore two DYn1 transformers connected in
series DYn1 - DYn1, the output will lag the input by 60
degrees but YnD1 - DYn1, the first stage results in the
intermediate voltage (Delta) leads by 30 degrees and at the
last stage, there is a 30 degrees lagging phase shift so
the sum phase shift from Y - Y is 0 degrees.

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