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This paper has the purpose to investigate the variation of electric field inside a HVDC cable insulation, and consequent potentiality of partial discharge inception in a defect upon load current variation. Simulations carried out by COMSOL Multiphysics show that load variations can incept partial discharges during cable operation at a constant voltage, depending on insulating material characteristics, defect size and location, and, in particular, the temperature and field dependence of electrical conductivity. Different values for temperature and field dependency of electrical conductivity, as well as of thermal conductivity and heat capacity are considered and their effect on the field distribution inside cavities near inner and outer semiconducting layer analyzed. For this purpose, a new analytical model to predict the behavior of PD amplitude and repetition rate from cable energization to steady state, including load variation, is introduced. The likelihood of PD inception during load transients, and not only voltage transients as previously demonstrated, poses further attention and constraints to HVDC cable design.

This paper focuses on the design of insulating materials candidate from DC-supply applications, proposing viable solutions that may increase the defect-tolerance of an insulation system and avoid the presence of highly energetic phenomena, specifically partial discharges, which can cause premature insulation breakdown. It is shown that, in principle, polymeric materials for DC insulation can be structured, possibly through nanotechnology, to avoid partial discharge inception in steady state even in UHVDC cables and high-field design insulation systems, which would exclude partial discharge degradation from the aging factors that can affect insulation reliability and life. This approach may provide basic tools to design DC insulation having electro-thermal life and reliability of virtually unlimited extent, thus of so-called PD-phobic materials. INDEX TERMS Cables, electro-thermal life, HVDC, insulation reliability, nano-filled materials, partial discharge (PD), partial discharge inception voltage (PDIV), polymeric materials.

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Dielectric polymer nanocomposites are considered as one of the most promising insulation material candidates for future capacitive energy storage applications, providing tailorability of charge trapping and transport properties at the...