Please help! Confusion with 30 degree phase angle shift between delta wye in a transformer

[poosri]

Hi All,

This phase shift seems to be killing me.

Based on Wildi,

if wye connected, V L-N = (V L-L/sqrt 3) at angle -30 degree

if delta connected I phase = (I line/sqrt 3) at angle -30 degree

But in the attached problems, eg. E-25, at the end, Ia seems to be calculated at -30 degree. I think Ia must be 173 at angle 10 degrees (+30-20)? same follows in problem E-26 Ia must be 300 at -20 degrees?

Thanks for your help/time!