Motor experts please.

[Ronnie Sullivan]

The results are in.
The 11 kw motor when free running had 2v ac across the winding connections
The 5kw had 10v.
Both zero volts when stopped - so nothing was induced.

 

[Gene Bond]

I've had a few machines like this, using 2 Soft Starters. They replaced a 2 speed motor with a 4pole and 6pole motor. The application was slow forward and fast reverse.

As far as generated power on the open motor, yes, there will be some voltage, based on the residual magnetism, as mentioned above. But, the actual power is negligible. With an open circuit on the contactor, there's no worry.

Just ensure the 2 motors are properly interlocked so they can't try to run at the same time.

 

[JesperMP]

The measurements makes sense to me.
The squirrel cage bars will pass through a weak magnetic field of the stator. This generates a weak current in the squirrel cage when the rotor is driven mechanically.
The current in the rotor in turn generate a voltage in the stator windings, albeit not very high.
If the voltage is more than 48V then it must be considered 'high voltage'. I agree that it is very unlikely.

 

[pal]

Did you check the rotation direction ? I have seen this set - up with the small motor used as a low speed reversing motor hence the interlocks .
( The load equipment could come apart with severe consequences if run in reverse at high speed }
Pal