Why can not apply unbalanced fault in transformer branch?

I don't want to impose an internal transformer fault， I want to think of the transformer branch as a transmission line with a certain length. Is it possible to understand that the transformer branch has no length, it represents only the transformer itself, so there is no concept of “position”

What kind of fault do you want to simulate? What do you mean with "different postion" if it is not an internal fault?

for example, if I set unbalanced fault in non-transformer branch, I can choose fault position like in 30% bettween bus i and bus j: i ---------30%----------------------------j

My thought is, look transformer branch as: i-------------------------trans--------------------------j, then I can choose fault position in line.

That is exactly what my answer is proposing. Split the transformer with 30% of impedance in first transformer and 70% in the second and apply the bus fault inbetween!