Proper application of motors operated on adjustable frequency control

Adjustable speed drives are becoming an increasingly popular process control method. The drive consists of a combination of a control, motor (or motors), and any motor mounted auxiliary devices. The term control refers to the electronic devices that control the DC or constant voltage and frequency AC power to a controlled output AC voltage and current. In the context of this paper, references to these are abbreviated as AFC (adjustable frequency control), and ASD (adjustable speed drive). Much has been written about the effect that AFCs have on motors over the last several years. Most of what has been written addresses details concerning the impact on winding insulation, reflected waves, rotor slots optimized for ASD application and other such motor design topics. The pragmatic issues concerning the application aspects of AFC operated motors have not been covered as well. In many cases, standard motors can be successfully utilized on AFCs without any modification. In some cases, minor motor modification is required. Properly applied, the AFC driven motor should have a life similar to the life of the motor operated on sinewave power.