Insulation of small and medium size motors - IGBT inverter fed

The latest IGBT type of adjustable speed drives (ASD's) produce over voltage with extremely high carrier frequency. The frequency may be as high as 20khz. 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 aging. This aging usually leads to premature failure of motors sometimes days or months after startup. Even new motors make this an issue. Harsh application conditions may also add to the problem. This paper will present approaches taken to deal with the motor insulation concerns of applying ASD power to less than 1000 V three phase motors.