Investigations on Different Polymers used for Insulation in E-Mobility Applications

Due to the demand for the reduction of greenhouse gas emissions, the importance of energy efficiency measures and energy conservation becomes a worldwide focus. The aim of reducing emissions is to limit the global rise of temperature in a short period to below 2 °C – if possible below 1.5 °C. In all areas of material usage and use of energy this goal is accompanied by the implementation of stricter rules. As a result, these developments also affect the energy and power sector. The increasing demand is accompanied by further development of production technology for e-motors. This development includes quality, life span and reduction of expenses. A common reason for unscheduled failures of rotating electrical machines are defects in the stator insulation. The production failures associated with the stator insulation failures are expensive and not economical. Because of this, a reliable insulation of stators is essential. Frequently occurring types of stator insulation faults are the delamination of the main insulation from the conductor, the delamination of the main insulation, micro voids, contamination, cracks, the deformation of the insulation, the variation of the thickness and slot discharges. Furthermore, the aging of the insulation material has a significant influence on the reliability of the stator insulation. Against this background, samples of polyamide 6 and polyamide 6.6 are investigated, which could possibly be used as slot insulation in a stator of an electric machine. For this purpose, the samples are subjected to thermal stress for different aging times, up to 1500 h, and investigated concerning the dielectric properties dissipation factor and permittivity. Due to the dependence of dielectric properties on temperature, these are measured at six different temperatures in a range between 25 °C and 155 °C. It has been shown for both materials that at a frequency of 50 Hz the dissipation factor tends to decrease with aging time. Air pockets and cracks due to thermal aging are the main cause of the decrease. For the temperatures and frequencies studied, polyamide 6 has a higher relative permittivity and dissipation factor compared to polyamide 6.6.