Bob Swinney wrote:
Brian,
The "speed" of reversing a 3-phase motor would be a function of how stiff
the 3-phase source is. A genuine 3-phase line being the quickest. I have
done this and it is hard to tell when stop-then- reverse occurs. It is
about as close as you can get to instantaneous. Following, I would guess,
is a good stiff, balanced, rotary phase converter such as the 25 HP one you
propose. Though I've not tried reversing with a VFD, I believe the smaller
the power rating of the VFD, the longer it would take to reverse a 3-phase
motor.

Based on my limited experience, it's based more on
the stored energy in the drivetrain and the braking
ability of the VFD. The VFD has to eat the energy
that it takes to stop the drivetrain so a little
VFD and a massive, fast drivetrain takes a long time
to stop without the VFD faulting.