Anjana Samarakoon with Advisor Prof. Kiruba S. Haran

The design of insulation for electrical machines used in electric vertical take-off and landing (eVTOL) aircraft has become increasingly complex due to demanding mission profiles, harsh operating environments, and the need for higher power density. These factors place significant stresses on the insulation systems of electrical machines, including thermally induced mechanical stress. Low-voltage electric machines typically employed in aircraft propulsion utilize Type 1 insulation, which must be designed to be free of partial discharge (PD). Traditional insulation designs often overlook the effects of thermally induced mechanical stresses on partial discharge inception voltage (PDIV) over time, as well as their dependence on operational duty cycles.

The objective of the Motor Winding Reliability research is to create a mathematical model to predict the PDIV of motor winding insulation based on results from accelerated aging tests. We plan to fabricate and test one hundred motorettes with varying temperature profiles. This predictive model will help assess the impact of temperature and cycle counts on PDIV drop, aiding in the evaluation of motor winding lifetime and establishing safe operating voltages for long-term PD-free operation.

The research comprises three main tasks: simulation, testing, and analytical modeling, all conducted in collaboration with NASA Glenn Research Center. Samples have been fabricated and impregnated with assistance from NASA. Initial aging tests revealed insulation degradation due to mechanical stresses during the curing process and high-temperature aging cycles. Ongoing tests are focused on studying thermal cycling aging at lower temperatures.

The finite element analysis (FEA) modeling and validation are complete, with the next steps involving the development of an analytical model and further testing to confirm its accuracy. The research also explores the behavior of PD in form-wound windings and its response under altitude pressure and high operating temperatures.

FEA simulated model of the winding and the cross-section of a motorette specimen.  The cross-sectional view shows the quality of the VPI

Insulation health monitoring and aging setup. (A) oscilloscope (B) specimen test stand (C) PD Base II (D) high current supply for specimen aging (E) variable AC power supply (F) Doble M4100 high voltage insulation tester (G) vacuum oven for PD measurements at high temperature and vacuum (H) specimen aging setup

Turn-to-turn Partial Discharge Inception Voltage variation with aging cycles