Partial discharges on low voltage stator windings subjected to voltage surges from adjustable speed drives

Random wound stator windings in motors operating in industrial applications have been reported to suffer from premature failures. Although several failure mechanisms exist, some of these failures have been caused by exposure to fast rise-time voltage surges coming from inverter drives. Dissection of failed stator windings have indicated that partial discharges have been a predominate cause of the stator failure. Partial discharges may occur between turns during fast rise-time voltage surges. Voltage surges of a sufficient magnitude can result in the degradation of the organic magnet wire enamel impregnants, eventually resulting in turn-to-turn or, phase-to-phase failures. This paper discusses the specific mechanisms, and the specific conditions under which partial discharges may occur in low voltage motor surge environments. Furthermore, this paper presents the characteristics of partial discharges measured during such surge conditions. Methods used to identify which stators are at risk are presented here, allowing for an assessment of the data acquired using voltage surge measurements.