It is worth repeating that the space vectors at some arbitrary time t
in Fig. 3-3 are expressed without a superscript “a” or “A.” The reason
is that a reference axis is needed only to express them mathematically
by means of complex numbers. In other words, these space vectors in
Fig. 3-3 would be in the same position, independent of the choice of
the reference axis to express them. We should note that the relative
position of is and ir is shown arbitrarily here just for definition purposes
(in an induction machine, the angle between is and ir is very large—
more than 145°).