Generator IPB Sizing

Short circuit rating = Rated full load current / X''d (subtransient reactance)

There is no MW restriction as such .....................MW rating can be any thing, rather there is voltage restriction. Sub transient reactance shall be used to determine the contribution from the generator

For Bus bar sizing you must always consider the lowest of the three reactances, X"d, X'd & Xd. Obviously, X"d is the lowest among the three and it must be considered for sizing the IPB.