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Can a VFD run a wound-rotor motor?

FA237558

24 January 2022

Issue:
Wound-rotor motor

Product Line:
Altivar drives

Environment:
All models and serial numbers

Cause:
None

Resolution:
Altivar variable frequency drives may be used to operate wound-rotor motors. 
Most wound-rotor motors are used where high starting torque is required so the Altivar 312, Altivar 32, Altivar 71 (obsolete) or the currently available Altivar 320, Altivar 340, or Atlivar 930 (sized for Heavy Duty) drive would be most suitable for this application. 
The wound-rotor motors use resistor to connect the rotor windings.  The resistance can be adjusted to control the speed/torque characteristics of the motor. 
To use a variable frequency drive with a wound-rotor motor the resistors would need to be shorted.  It is not appropriate to switch the resistance when operating on a VFD.
It is also recommended to use a dv/dt filter on the output of the drive to smooth the PWM.