Aging effects and failure mechanisms of wire insulation when exposed to high voltage gradients

• Applicants: Privatdozent Dr.-Ing. Martin Dazer; Professor Dr.-Ing. Stefan Tenbohlen
• Subject Area: Electrical Energy Systems, Power Management, Power Electronics, Electrical Machines and Drives ; Synthesis and Properties of Functional Materials
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 551038671

The longevity of electrical machines, particularly in electromobility, represents essential ecological and economic factors. Defects lead to downtime, additional costs, and negatively impact the CO2 balance. A significant contribution to the lifespan of high-power density electric drive machines is made by the permanent function of the machine's electrical insulation. Determining the reliability and lifespan of this insulation is an open question, especially since electrical loadings on insulation systems become more critical due to new inverter technologies: higher operational voltages and shorter switching times result in increased electric field strengths connected with steeper voltage gradients. Combined with additional influencing factors (temperature, humidity), potentially new damage mechanisms are triggered that can reduce lifespan. These types of damage are largely unknown in industrially relevant applications so far. This project aims to close the research gap and clarify which damage mechanisms (delamination, cracking, partial discharges) are primarily responsible for insulation degradation during operation, so that degradation and aging behavior can be modeled. This is realized through experimental measurement series as a Design of Experiment (DoE) in a specially developed test setup that allows for variable environmental conditions as well as freely adjustable electrical loading. Degradation effects are evaluated alongside measurement results based on extensive diagnostics. Since it is not yet conclusively determined which measurement metric is most suitable as an indicator for qualitative and quantitative assessment of degradations, this includes various methods for comparison: non-destructive methods (partial discharge behavior, insulation resistance / leakage currents, complex impedance analysis / tan delta, imaging procedures like X-ray analysis) as well as destructive methods (section images for determining insulation thickness, determination of final breakdown voltage after aging). The methodological diagnostics along the aging tests, for example, show whether the reduction of the partial discharge inception voltage (PDIV) represents a suitable aging indicator. From the measurement results, a statistical-empirical aging model is derived. This allows for a statistically validated estimate of insulation aging depending on the load spectrum. The statistical results and the results of the diagnostics are combined and serve as the basis for the assignment to known physical principles. By linking the statistical measurement data (e.g. PRPD pattern) of failure mechanisms and consequences, a physics of failure model is created, thus gaining insights that allow future derivation of underlying failure mechanisms from the measurement data.

• DFG Programme: Research Grants
• International Connection: Italy, Sweden
• Co-Investigator: Dr.-Ing. Michael Beltle
• Cooperation Partners: Professor Dr. Andrea Cavallini; Professor Dr. Thomas Hammarström