Abstract
Among the various requirements that high voltage direct current (HVDC) insulation materials need to satisfy, sufficiently low electrical conductivity is one of the most important. The leading commercial HVDC insulation material is currently an exceptionally clean cross-linked low-density polyethylene (XLPE). Previous studies have reported that the DC-conductivity of low-density polyethylene (LDPE) can be markedly reduced either by including a fraction of high-density polyethylene (HDPE) or by adding a small amount of a well dispersed, semiconducting nanofiller such as Al2O3 coated with a silane. This study demonstrates that by combining these two strategies a synergistic effect can be achieved, resulting in an insulation material with an ultra-low electrical conductivity. The addition of both HDPE and C8–Al2O3 nanoparticles to LDPE resulted in ultra-insulating nanocomposites with a conductivity around 500 times lower than of the neat LDPE at an electric field of 32 kV/mm and 60–90 °C. The new nanocomposite is thus a promising material regarding the electrical conductivity and it can be further optimized since the polyethylene blend and the nanoparticles can be improved independently.
Highlights
The growing global demand for renewable sources of energy in creases the need for transporting electrical energy over large distances with minimal losses [1]
It was concluded that the electrical conductivity of low-density polyethylene (LDPE) can be significantly reduced by adding small fractions of either high-density polyethylene (HDPE) or metal-oxide nanoparticles such as octyl-coated aluminium oxide
The addition of 4 wt% HDPE to the LDPE resulted in a moderate decrease in conductivity (~2–10 times), while the addition of 3 wt% C8–Al2O3 caused a larger drop (~200 times)
Summary
The growing global demand for renewable sources of energy in creases the need for transporting electrical energy over large distances with minimal losses [1]. A suitable HVDC insulation material should have good thermal and mechanical properties as well as excellent electrical characteristics – high electrical breakdown strength, low dielectric permittivity, low space charge accumulation, low tendency for electrical treeing, low electric conductivity – in order to fulfil the demanding long-term requirements [2,5]. Among these requirements, an exceedingly low electrical conductivity is important [6,7,8]. If an additive or synergetic effect were observed, this would indicate that the conductivity reductions with HDPE and nanoparticles are due to two different mechanisms and that the polymer matrix and the nanoparticles have the potential to be optimized independently
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