Will your motor insulation survive a new adjustable-frequency drive?

The latest family of insulated-gate-bipolar-transistor (IGBT)-type adjustable-frequency drives (AFDs) produce voltage wavefronts that are extremely fast as a result of increasing carrier frequency. The frequency may be as high as 20 kHz. Motors which are designed for low-voltage sinusoidal power run more efficiently and quieter under this condition. However, the insulation in small- and medium-size motors may experience undesirable stress, resulting in accelerated aging. This aging usually leads to premature failure of motors, sometimes days or months after startup. Even new motors make this an issue. Harsh environments may also add to the problem. This paper presents a practical approach to the motor insulation concerns of applying AFD power to less than 1000 V three-phase older motors and give specification details on new motors for AFD service.