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In a world increasingly facing new challenges at the forefront of plasma scientific research and technological innovation, CNR and ISTP pledge progress and achieve an impact in the integration of research into societal practices and policy

WP-6: Laboratory of High Voltage insultation in fusion devices

RESEARCH UNIT: ISTP-Padova
WP LEADER: NICOLÒ MARCONATO

The knowledge of the physical mechanism governing the vacuum breakdown still remains an open issue although
decades of research activities were dedicated to study this topic. This WP proposes the creation of an advanced laboratory for the study of electrical insulation related issues in fusion machines. The main topics are high and extra-high voltage insulation in vacuum and pressurized gases, composed of two activities: the refurbishment and upgrade of the facilities of the High Voltage Padova Test Facility (HVPTF) for the study of vacuum insulation in high and very high voltage systems and the setup of a new feature of the HVPTF for the study of pressurized gas electrical insulation properties in high and very high voltage systems.

GOALS

The most relevant outcome of this WP will be: 

  • Improving the existing experimental facilities of the VHPTF in order to propose, explore and identify innovative strategies needed to satisfy the 1MV DC requirements 
  • Consolidation of a multidisciplinary experience grouping knowledge in the electrical engineering, metallurgy, applied physic and vacuum technology areas, in order to investigate the role played by the electrode material, geometry, surface finishing and pressure conditions on the electric insulating performances of particle accelerator for the heating of fusion plasmas, as well as of all applications where high voltage insulation in low pressure conditions needs to be sustained. 
  • Investigation on the breakdown statistics to optimize voltage holding conditioning procedure and to validate and fine-tune numerical models specifically implemented, which need to be tested in relevant conditions close those expected in fusion environments. 
  • Enhance the knowledge of the physical mechanism governing the vacuum breakdown, supporting the
    development and validation of new physical models. 
  • Testing specific diagnostic system, such as photon detectors, as well as components specifically designed for vacuum insulated system, such as spark gaps or standoff insulators. 
  • Design and realization of a real size facility dedicated to study insulation properties of pressurized gas in HVDC condition, with detailed study of the phenomena involved in gas insulated HVDC system, such as charge carrier accumulations on dielectric interfaces with validation and fine-tuning of advanced numerical models specifically developed for the correct simulation of the
    complex strongly nonlinear phenomena involved. 
  • Experimentation on alternative insulating gases to SF6, such as gas mixtures consisting of natural substances (N2, O2, CO2), or synthetic substances (e.g. fluoronitriles or fluorochetones).

Background

The HVPTF has been used to tests stainless steel electrodes insulated by high and medium vacuum, and the experimental results have been used to benchmark a probabilistic code able to predict the maximum hold off voltage of a generic system insulated by vacuum with a generic electrode geometry.  
The design and the installation of a new system composed by an improved vacuum vessel, upgraded cables and
feedthroughs will face one of the main issues observed after several years of operations in the HVPTF , which is the reliability of the system against the energetic vacuum arcs (>500kV), usually occurring during the experimental campaigns. 
Moreover, in many applications from the industry to fusion technology, where high power must be transmitted in high voltage DC lines with a high level of compactness and reliability, the choice of Gas Insulated Lines (GIL) would have several advantages to feed high power system in fusion facilities (higher transmission capacities, low losses, and greater overload capabilities than other cable technologies).
Whether the GIL technology in AC is mature and widely adopted in commercial application, HVDC GIL technology must face various issues still unsolved, like charge carrier accumulations on dielectric interfaces, which may lead to a decrease in  flashover voltage, requiring the understanding of the physical processes and factors of influence on the electric field distribution. The design, procurement and installation of a new system composed by a real size pressure vessel with proper air-gas bushing, HV power supplies rated to 500 kV, suitable diagnostics for gas monitoring and measurement of electric properties, and with appropriate acquisition and control system will face this relevant issue.

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CONTACTS

COMMUNICATION AND INFORMATION:
comunicazione@istp.cnr.it

WP leader:
nicolo.marconato@igi.cnr.it

 

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