Dyn11 is vector group notation of tansformer.It means LV winding,which is star connected (written in small letters means LV side and vice versa)is 30 degrees lagging by HV winding which is delta connected.In India we go for +-30 deg connection of transformer.
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D = Delta connection at primary,y = Star connection at secondary and n = neutral point connected at secondary.
Dyn 11 means that the voltage of the secondary star winding lead the primary phase voltage by 30 degree and it corresponds to 11 o’clock.
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