Moving Toward Partial Discharge-Free Design of Electrical Machines for More Electric Aircraft Applications

For aerospace electrical machines (EMs), the partial discharge (PD) risk is becoming much more severe due to higher dc link voltage levels and faster switching devices. Traditionally, EMs for safety-critical applications mainly rely on overengineering methods to guarantee reliability. However, a recent shift toward reliability-oriented design, which is based on understanding the physics of failure, allows for meeting the reliability requirements while ensuring performance. From the perspective of the reliability-oriented methodology, the PD-free design of a starter/generator (S/G) with a 540-V dc bus is presented and the main steps for a comprehensive PD risk evaluation are discussed. First, the PD inception mechanism is experimentally investigated under pulse voltage excitation for several rise times, temperatures, and pressure values. Then, the measured PD inception voltage (PDIV) values are used to perform an accurate PD risk assessment, which includes the winding hotspot temperature resulting from the S/G mission profile, the environment operating conditions, and the connection cable length. Finally, the PD risk of an S/G with a higher dc bus (i.e., 800 V) is examined to comply with the future aircraft voltage level.