I. Introduction
In low-voltage traction drives, the DC-link voltages are increasing to achieve a faster battery charging process keeping the current level constant. Additionally, SiC-MOSFETs are used to increase the switching frequency and reduce power electronic switching losses [1]. The use of SiC-MOSFETs causes higher inverter slew rates compared to conventional Si-IGBTs. The resulting overvoltages lead to higher electric fields inside the machine and thus to higher electrical loads on the insulation system [2]–[4]. If the critical voltage inside the insulation system is exceeded, partial discharges can occur. Low-voltage electrical machines are designed to be PD-free at any operation point by standard [5]. The critical voltage can be increased by applying a thicker insulation which decreases the copper filling factor of the machine. If the insulation is exposed to partial discharge, this leads to electrical aging and erosion. After a certain time, depending on parameters such as switching frequency, voltage and material data, the insulation can not longer withstand the electrical load resulting in the breakdown of the insulation [6]. It is known from literature that the winding insulation is usually the weakest element [2]. The expected lifetime for conventional enameled wires reduces to a few hours or less. Another possibility of facing the higher demand on the insulation is to use corona-resistant insulation materials which can withstand electrical loads significantly longer.