"Steve Lusardi" wrote in message
...
John,
Excellent description. You are correct, but I know of no VFD unit that
increases voltage with frequency. The effect is that current drops from
rated with frequency above rated frequency, but speed increases limiting
somewhat the drop in net power. Overheating of the motor occurs at
frequency below the motor rating without reducing the applied voltage.
Again, I know of no VFD that reduces voltage either.
Steve


You can set a number of parameters on the newer VFD's including current
limiting which in effect does this by voltage limiting. Much of the motor
heat comes from resistance losses. some from friction and the rest from eddy
current losses in the magnetic material. you can ramp the current and
therefore voltage in relation to frequency similiar to a soft start unit
used on larger hp motors.


John