Influence of some voltage waveform characteristics on the partial discharge patterns: application to a PWM power supply

Different solutions have recently been proposed to address the problem of premature failure of rotating machines fed by inverters. Among them, the "shielding" of the enamel wires by an inorganic coating appears particularly interesting. Its main goal is to offer an increased resistance to partial discharge (PD) actions. The underlying idea of the proposed reinforcements does not consist therefore in increasing the PD inception voltage but in enhancing enamel resistance to PD activity. Despite their interest, there is a lack of knowledge concerning the behavior of such materials during aging. In this paper, the authors present the first result of the influence of different voltage waveform characteristics and external conditions on the discharge inception voltage and PD patterns of different materials. Samples are twisted pairs of enamel wires with or without reinforcement of different size coming from different manufacturers. These characteristics are determined prior and after aging. For the conditions under study, some conclusions may be drawn and are discussed according to lifetime measurements performed on the same kind of samples. The need for a normalized test, taking into account the specificity of the applied stresses, is demonstrated.