Abstract
Partial-discharge (PD) testing has long been an important tool for assessing the condition of the high-voltage insulation in motor and generator stator windings. In the past several years, many motors have been powered from inverters, which facilitate variable-speed motor operation. The most common drive used today is the voltage-source pulse-width modulation (VS-PWM) type. VS-PWM drives rated up to 13.8 kV are becoming more common in natural gas processing plants, as well as in other petrochemical facilities. Such drives generate high-voltage impulses in the kilovolt range with rise times in the submicrosecond range. These impulses are a form of severe electrical interference that can make difficult the online detection of PD (with magnitudes 1000 times smaller) due to the overlapping frequency content in PD and in the impulses. Thus, PD detection on medium-voltage VS-PWM systems has been a challenge in spite of the serious stator winding insulation aging that such drives may cause to these motors. This paper discusses the stator winding failure mechanisms that produce PD, including the insulation problems that VS-PWM drives can accelerate. A research project that lasted several years is reviewed. This project culminated in a prototype online PD monitoring system suitable for motors fed by VS-PWM drives.
Published Version
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