Lifetime Model for Inverter-Fed Electrical Machines Windings Including Thermal Aging and Partial Discharge Risk

Reliability is a paramount feature in electrical machines (EMs) designed for mobility applications and the demand for high-performance EMs poses a serious threat to the electrical insulation system (EIS) integrity. In high-performance EMs, the EIS is exposed to enhanced stresses, such as undesired thermal aging and partial discharge (PD) risk. In accordance with IEC 60034-18-41, the inception of PD is considered as an EIS end-of-life criterion, and a thermal aging enhancement factor (EF) is introduced in PD risk assessment for including EIS thermal degradation. These recommendations enable the EM PD-free design but do not allow the insulation lifetime evaluation under thermal and electrical stresses, which would ensure the reliability level required by a given application since the first EM design steps. To tackle this challenge, a tailored windings lifetime model for inverter-fed EMs is proposed and built relying on an extensive experimental database. The PD inception voltage (PDIV) values are collected over an accelerated thermal aging tests campaign involving three aging temperatures and at least ten diagnostic sub-cycles per aging temperature. The derived winding lifetime model is meant to be used during the EM design process for reliability check and it is applicable to a variety of transportation applications by simply updating the PDIV threshold according to interturn voltage and environmental conditions. The applicability and versatility of the proposed winding lifetime model are proved through two transportation study cases (i.e., automotive and aerospace).