Answer / salah

Dyn11-secondary voltage lags primary by 30degree

Dyn1-secondary voltage leads primary by 30deg

hence it is not satisfying the condition for
pare;;alisation .

if we connect two TR in parallel current drwn form the
source by both transformer is not in phase hence
circulating current will produce & damage the winding as
well in secondary aslo

Answer / tanesh

When DYn11 and DYn1 are out of phase by 60deg. Although the magnitude of both transformers are same, but phase different would cause potential difference between the transformers. This will cause short circuit the two transformers are paralleled.

Answer / debashisdb

Doug - you are absolutely right for Dyn1. To look at this graphically, a positive 30 degree angle of secondary to primary means that secondary voltage sinusoidal wave starts 30 degrees after the primary sinusoidal wave. Hence in reality it is indeed lagging the primary. Just reverse for Dyn11.

Answer / 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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