Speaker
Description
The design and operation of magnetic confinement fusion devices and associated high-power systems require reliable electrical insulation solutions capable of operating under extreme conditions. In particular, several subsystems of fusion facilities—such as Neutral Beam Injectors (NBIs) and high-power transmission infrastructures—operate at high or extra-high voltage levels, where insulation performance becomes a critical technological challenge. Within the NEFERTARI project, Work Package 6 has been devoted to the development of an advanced experimental laboratory for the investigation of high-voltage insulation phenomena relevant to fusion applications, focusing on both vacuum and pressurized gas environments.
The activities have been carried out at the High Voltage laboratory of the Industrial Engineering department of the University of Padova, where the High Voltage Padova Test Facility (HVPTF) has been operating since 2010. The facility is capable of performing high-voltage DC tests in high and ultra-high vacuum conditions, applying voltages up to 800 kV on a single vacuum gap. One of the main objectives of the work package was the refurbishment and upgrade of the existing experimental setup dedicated to vacuum insulation studies. Vacuum represents an attractive insulating medium due to its environmental compatibility and its excellent dielectric properties; however, the physical mechanisms governing electrical breakdown in vacuum remain only partially understood despite decades of experimental investigations. The upgrade of the HVPTF facility involved the improvement of the vacuum system, the installation of new high-voltage feedthroughs, the enhancement of diagnostic capabilities, and the implementation of improved environmental control of the laboratory. These upgrades were necessary to increase the reliability of the system and to mitigate the effects of energetic vacuum arcs that may occur during high-voltage experiments, enabling more stable and reproducible experimental campaigns.
In parallel, a second major objective of WP6 was the design and realization of a completely new experimental facility dedicated to the study of electrical insulation in pressurized gases under high-voltage DC conditions. Gas-insulated transmission technologies are widely used in high-power electrical systems due to their compactness, high reliability, and low transmission losses. In fusion facilities, Gas Insulated Lines (GIL) represent an attractive solution for supplying high-power systems such as Neutral Beam Injectors. However, while AC gas-insulated technologies are mature and widely adopted in industrial applications, several open issues remain in the case of HVDC systems. In particular, the stationary electric field distribution along insulating structures under DC voltage is strongly influenced by charge transport processes and charge accumulation at gas–solid interfaces, which can significantly affect insulation performance and reduce the flashover voltage.
The new experimental facility developed within WP6 includes a real-scale pressurized vessel equipped with high-voltage bushings, electrodes, and dedicated diagnostic systems, together with a high-voltage DC power supply rated up to 500 kV and a dedicated data acquisition and control system. This infrastructure enables systematic investigations of insulation phenomena in gas-insulated HVDC systems, including the study of charge carrier transport, surface charge accumulation, dark currents injected by high-voltage electrodes, and the influence of environmental factors such as temperature, humidity, and particle contamination. Particular attention is also devoted to the investigation of alternative insulating gases and gas mixtures with lower environmental impact than SF₆, contributing to the development of more sustainable solutions for high-voltage technologies.
In addition to experimental investigations, the experimental activities also support the development and validation of advanced numerical models for the simulation of electro-quasi-static phenomena in HVDC gas-insulated systems. These models aim at capturing the complex interaction between electric fields, charge transport mechanisms, and material properties, including effects such as radiation-induced conductivity (RIC) that may occur in fusion environments. The combined experimental and modeling approach provides a powerful framework for improving the understanding of insulation phenomena and for supporting the design of reliable high-voltage components for future fusion devices.