For the transformers in parallel.. there's a relation Z1/Z2 = S2 (rated)/S1(rated) where Z1 & Z2 are the impedences while S1 & S2 are KVA ratings of the two transformers. Now why we are taking rated KVA values..?? I mean if Z1/Z2 < S2(rated) / S1(rated)... we increase S1 to satisfy the relation but we are already taking the rated value..so we can't increase it...!!! Maybe I am going wrong.. please correct if I am mistaken..basically I want to understand the relation practically...!!