Fillet Radius Impact of Rectangular Insulated Wires on PDIV for Turn-to-Turn Insulation of Inverter-Fed Motors

This contribution elucidates the impact of the fillet radius (FR), a geometric feature of rectangular insulated wires not commonly considered, on the partial discharge inception voltage (PDIV) in low-voltage machine turn-to-turn winding insulation. Initial PDIV tests involve edgewise-insulated wire samples with a reference FR. These measurements are performed under constant conditions: 30 degrees C temperature, 35% relative humidity (RH), and atmospheric pressure (1000 mbar). These tests are carried out under ac 50-Hz excitations, following IEC 60034-18-41 guidelines for inverter-fed motor insulation system qualification. Subsequently, a probabilistic PDIV predictive model is developed based on Schumann's streamer inception criterion (SCSIC). This expanded model then analyzes and forecasts the impact of the FR on PDIV and its associated dispersion level, within the context of the two-parameter Weibull distribution and the given environmental conditions. Furthermore, a novel method is presented to understand partial discharge (PD) phenomenology and its destructive potential in rectangular insulated wires with varying fillet radii. This approach employs SCSIC-derived streamer inception parameters (SIPs): critical field line length (CFLL), air effective ionization coefficient (alpha(eff)), PD inception field (E-inc), and firing voltage (V-firing). The developed probabilistic predictive model enables the selection of an optimal FR value, facilitating the creation of a reliable insulation system with maximum PDIV and minimal PD-related damage.