It is obvious that effect of stator current suppressed is very
good in all those various transform point. In other words,
stator current during transform can be suppressed well enough
by wye-delta soft transform. However, effect of current in
figure 8 (d) is best for two main reasons. The first is that
inrush current in transform is steady and small enough. The
second is that operation of motor change immediately into
steady state after soft transform from wye to delta. That is, area
of region B in the figure 8 (d) is nearly zero.