Opening lecture
In pursuit of electrical ageing mechanisms in polymeric insulations: Current status and trends for the future
Gilbert Teyssedre, Laplace, Université de Toulouse and CNRS, Toulouse, France
Abstract: The approach to more efficient energy conversion and transmission systems has led to tougher specifications for insulating materials used in power equipment: higher service temperature, higher service field and demand for longlife materials in service. These evolutions have typically led to service fields of the order of 8kV/mm under 320 kV HVAC cables to typically 30 kV/mm for 520 kV HVDC cables representing a huge gain in transmission capacity per cm of insulation thickness. Thin films capacitors work with service field beyond 100 kV/mm. In the field of power electronics, combined local high temperature and high electric field, with diverging geometry are the challenge to go to wide band gap semiconductors. All along progresses in developing materials and exposing them to new stresses, there has been a salient question: do materials deteriorate under electrical stress, how, and how to anticipate their end.
The considered mechanism is the following: due to ageing factors, the material integrity evolves and its cohesion weakens, leading to embrittlement to a point it cannot oppose to the propagation of treeing. Then, the cause roots of material evolution need to be found. While it is relatively straightforward identifying it in hydrolytic or oxidative environment, processes under pure electric stress are more difficult to demonstrate. My purpose in this lecture will be to review current knowledge in this field, particularly as regards the access to the cascade of events that lead to a loss of dielectric strength in insulations.
Gilbert Teyssedre (Senior Member, IEEE) earned an engineering degree in materials physics and a master’s degree in solid-state physics from the National Institute of Applied Sciences (INSA) in Toulouse in 1989, followed by a PhD from the Solid-State Physics Laboratory at Paul Sabatier University in Toulouse in 1993, for a work on ferroelectric polymers. He joined the French National Centre for Scientific Research (CNRS) in 1995 and has since worked at the Laboratory of Electrical Engineering (now Laplace – Laboratory of Plasmas and Energy Conversion), a joint research unit between the CNRS and the University of Toulouse. His research interests include the development of luminescence techniques in insulating polymers, with a focus on chemical and physical structure, degradation phenomena, space charge, and transport properties. He is currently a senior researcher at CNRS. He led the Solid Dielectrics and Reliability Group at Laplace from 2004 to 2015. Dr. Teyssedre has served in the Scientific Committee of several conference series, including CEIDP, ICD, ICEMPE, ISEIM and JiCable. He was conference chair of ICD 2024. He has been an associate editor of the IEEE Transactions on Dielectrics and Electrical Insulation since 2021.
e-mail: [email protected]
2026 Thomas W. Dakin Distinguished Technical Contributions Award
Recent developments in electro-thermal life modelling of HVDC cables
Giovanni Mazzanti, Department of Electrical, Electronic and Information Engineering (DEI), University of Bologna, Bologna, Italy
Abstract: This paper aims at illustrating the recent developments in the field of electro-thermal modelling the life and reliability of HVDC cables, with focus on the contributions provided by the author. The technical-scientific significance of this work stems from the fact that the models used to estimate the life and reliability of HVDC cables (and cable systems) are fundamental, as they foster power system reliability and resilience.
In the first part of the paper, an introductory theoretical background shows the derivation of the popular phenomenological IPM-Arrhenius life model holding under constant electrical and thermal stress, which is taken as a reference by major international Standards and Recommendations for HVDC cables. The IPM-Arrhenius model is compared with the physical DMM life model. The IPM-Arrhenius model is also cast within an ad hoc probabilistic framework to enable the consideration of volume insulation enlargement effects and the estimation of reliability for a whole HVDC cable system with accessories. The theoretical background is closed by showing how the IPM-Arrhenius model can be used in an algorithm for life and reliability estimation of HVDC cables subjected to transient electric and thermal stresses.
In the second part of the paper, the algorithm for life and reliability estimation of HVDC cables subjected to transient electric and thermal stresses is applied to some practical cases. The first case is relevant to HVDC cables subjected to Type Test load current cycles according to Cigrè Technical Brochure 852; here the algorithm based on the traditional macroscopic approach to electrical conductivity and field computation is compared with a recently-developed microscopic approach relying on an ad hoc Bipolar Charge Transport model. Then, the algorithm is employed to estimate the life of HVDC cables subjected to transient voltages, such as long Temporary Over-Voltages (TOV), Superimposed Switching Impulses and Damped Transient Oscillating Voltages arising from switching operations of Direct Current Circuit Breakers. These results are compared with the experimental outcomes of aging tests on polymeric insulation specimens subjected to the combination of DC voltage plus TOVs. A final discussion emphasizes the limits of the presented life models and singles out possible innovative avenues for future research.
Giovanni Mazzanti (IEEE Fellow “for contributions to HVDC cable systems“, and recipient of the 2026 IEEE DEIS Thomas W. Dakin Distinguished Technical Contributions Award) is professor of High Voltage Engineering & HVDC Technology, Electrical Technologies & Power Quality at the University of Bologna, Italy. His research topics are reliability & diagnostics of HV insulation, power quality, renewables, human exposure to Electro-Magnetic Fields. He is consultant to TERNA, the Italian TSO. He is author or coauthor of 370 published papers (h-index=40 on Scopus, 41 on ResearchGate) and of the book Extruded Cables for HVDC Transmission: Advances in Research and Development, Wiley-IEEE Press, 2013. He is chairman of the IEEE DEIS Technical Committee (TC) on “HVDC cable systems”, and member of: IEEE Power and Energy Society (PES), IEEE Dielectrics & Electrical Insulation Society (DEIS), IEEE DEIS TC on “Smart grids”, IEEE PES Transmission & Distribution Committee (HVDC & FACTS Subcommittee), IEC TC 20, Cigré, Cigré JWG B4/B1/C4.73, Cigré WG-B1.91, Cigré SC-B.1, European Commission Implementation Working Group on HVDC Set Plan. He is co-Editor of the IEEE Transactions on Dielectrics and Electrical Insulation.