Electrical Insulation Design and Qualification of a SiC-based Generator-Rectifier Unit (GRU) for High-Altitude Operation

Silicon Carbide (SiC) devices are highly desirable in aircraft generator-rectifier units (GRUs) as they can offer significant improvements to the converter system efficiency, power density and specific power. However, the combination of the higher system voltages and the lower breakdown electric field (E-field) of air at high altitudes can initiate surface discharges, especially along exposed metal or insulator surfaces, in the GRU components and their assembly. This paper presents the insulation design and qualification of a SiC based GRU for partial discharge (PD) free operation at 15,200 m (50,000 ft) air pressure. Critical areas of the GRU prone to high E-field are identified and preemptively addressed in the design to prevent PD under normal operating conditions. A high altitude PD test bed is designed to qualify the GRU assembly under a test pressure of 11.599 kPa (87 Torr) to emulate the working environment at 15,200 m and experimental data are presented to validate the design.