With vector law of paralleowgram of forces shifting would be zero when all three forces are equal and 120 degree to each other. If not then there would be appearance of resultant force equal in magnitude and direction of unbalanced voltage for isolated neutral. If neutral is connected then resultant of all three unbalanced currents would flow from NG connection.
You should calculate a (geometrical) sum of voltage phasors of all the 3 phases. This sum (named sometimes neutral displacement voltage) equals to zero at symmetrical regime and is different from zero at non-symmetrical regime.
Thanks for all of you, of course you are right, but it seems to me it must be another thinking for finding new ides for calculation this case, and analyze situations accordingly... Thanks for all of you again...