Impedance of DG & Transformer

I am no authority on this but I'll offer what I think is the basic difference.

The impedance of a transformer is essentially static. That is, it never changes except in response to a change in frequency of the applied voltage.

However, the impedance of a generator, while being characteristic of its design, is dynamic in that it is speed dependent.

Hopefully, someone out there has experience with generator design and can offer a more intelligent explaination. Then we will both learn.