The insulation of state-of-the-art extruded high voltage direct-current (HVDC) power cables is composed of cross-linked low density polyethylene. Driven by the search for sustainable energy solutions, concepts that improve the ability to withstand high electrical fields and, ultimately, the power transmission efficiency are in high demand. The overall performance of an HVDC insulation material is mainly limited by its residual electrical conductivity. In this work, we demonstrate that the addition of small amounts of high-density polyethylene (HDPE) to a low-density polyethylene (LDPE) resin results in a drastic reduction in DC conductivity with increased mechanical and structural integrity above the melting point of LDPE. An HDPE content as low as 1 wt % is found to introduce a small population of thicker crystalline lamellae, which are finely distributed throughout the material. The change in nanostructure correlates with a decrease in DC conductivity by approximately 1 order of magnitude to about 10−15 S m−1 at high electric fields of 30 and 40 kV mm−1 and elevated temperature of 70 °C. Furthermore the blend system is found to be miscible in the melt, thus facilitating the formation of a solid-state microstructure with a fine distribution of HDPE-rich lamellae. This allows for a significant improvement of the mechanical integrity above the melting temperature of LDPE. The observed absence of creep is explained via the existence of tie-chains and trapped entanglements that create a physically cross-linked system through the remaining HDPE crystallites. This work opens up an alternative design concept for the insulation of HVDC power cables.

Correlation between phase-behavior and thermo-mechanical properties of a melt-miscible blend

254th National Meeting (2017)

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