Generator Specification Meaning Xd' and Xd"?

See [for instance]:

http://www.fecime.org/referencias/npag/chap5-46-77.pdf

thank you for your good explaination at this article, but my concern is precentage of this describe what? of generator.?

Seems to me to explain the saturation- and the unsaturation percentage of the magnetic coils.

Xd' unsat means unsaturated transient synchronous reactance where as Xd"sat means saturated sub_transient synchronous reactance. suffix d represents direct axis values. The statement Xd'unsat = 20.7% max means that for the generator under question should not have unsaturated transient synchronous reactance more than 20.7%. This limit is put to control the transient stability of the generator (P = EVSinδ/Xd'). So higher value of Xd' would reduce value of P. The statement Xd"sat = 11.7% min means that the generator should have minimum 11.7% value of Xd". This minimum value is required to limit the fault current which in turn would control the size of the generator circuit breaker. So maximum values of Xd' unsat and minimum value Xd" sat always form part of generator specification.

Thank you for your clear explanation