Use of Design of Experiments (DoE) predictive models as a method of comparison of enameled wires used in low voltage inverter-fed motors

The electrical insulation system of low voltage motors is exposed to new hazards since the introduction of power electronic power supplies. Fast changing voltage fed by long connecting cable between the frequency inverter and the motor can result in high overvoltage at machine's terminals, which can lead to partial discharge (PD) activity. Primarily the insulation of the magnet wire, a very thin enamel layer, is particularly endangered by this phenomenon, as it can resist PD activity only for very short time. This will lead to premature breakdown of a machine. This paper proposes a methodology allowing to compare magnet wires basing only on relatively quick aging tests but providing reliable predictions concerning much lower stress levels. This method is based on the Design of Experiments and applies Weibull statistics. It also allows to take into consideration the dispersion of the results. Model predictions are experimentally verified in order to prove the efficiency on this method.