Considerations in derating induction motors for applications on variable frequency drives

The basic operational features and special operational considerations of controlling industrial motors with variable frequency drives (VFDs), particularly those featuring pulse width modulation technology, are described. The consequences of using VFDs on the motor insulation and cooling system are discussed, and approaches to ensure reliable system designs are recommended. It is shown that proper sizing of the motor for common applications makes the use of standard NEMA design A and B motors possible with a high degree of confidence and that, for specialized duty, it is necessary to carefully engineer the VFD and motor system simultaneously