Abstract
Extruded high voltage direct current (HVDC) cable systems contain interfaces with poorly understood microscopic properties, particularly surface roughness. Modelling the effect of roughness on conduction in cable insulation is challenging, as the available results of macroscopic measurements give little information about microscopic charge distributions at material interfaces. In this work, macroscopic charge injection from interfaces is assessed by using a bipolar charge transport model, which is validated against a series of space charge measurements on cable peelings with different degrees of surface roughness. The electric field-dependent conduction and charge trapping effects stimulated by the injection current originating from rough surfaces are assessed. It is shown that by accounting for roughness enhanced charge injection with the parameters derived in part I of the paper, reasonable agreement between computed and measured results can be achieved at medium field strengths (10–40 kV/mm).
Highlights
High voltage direct current (HVDC) cable systems allow for long-distance energy transmission and can be used as interconnectors between power grids or for offshore wind integration
An inherent feature of XLPE-based HVDC insulation systems is charge accumulation in the material due to long-lasting unipolar electric fields inducing the transport of charge carriers through the insulation
The level of the recombination rates involving mobile carriers (S1-3 ) shown in measured space charge distributions are shown in the figures for comparison
Summary
High voltage direct current (HVDC) cable systems allow for long-distance energy transmission and can be used as interconnectors between power grids or for offshore wind integration. While HVDC cables using conventional mass-impregnated or lapped paper insulation have been used reliably for a long time, recently developed insulation materials such as crosslinked polyethylene (XLPE) have been developed for a voltage level of 525 kV [1]. Such extruded HVDC cables are in high demand, owing to their cost-efficient jointing and manufacturing processes. To utilize their capacity to the fullest extent and to secure reliable operation, physical processes in extruded cable insulation stimulated by the combined effect of strong electric fields and thermal stresses need to be further understood. The amorphous and Energies 2020, 13, 1750; doi:10.3390/en13071750 www.mdpi.com/journal/energies
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