Enhanced Electrical and Thermal Rating Power Cables for Renewables Connections in Developing Countries

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The world faces a major challenge, namely, how to supply energy to a growing population reliably, economically and without causing severe environmental damage. Looking forward, it is inevitable that our reliance on electricity will increase, as transport and heating become increasingly electrified, and that this increase will be largely met by renewable sources. Such facilities will be constructed at locations where prevailing conditions are appropriate and, in the UK, an example relates to plans to develop major offshore wind resources in the North Sea. However, the construction of large offshore facilities and the transmission of the resulting electricity back to shore is still very expensive and, therefore, it is imperative that this is done efficiently.All electrical plant relies upon electrical insulation and, today, this is primarily based upon polymers. While these materials are excellent electrical insulators, they are also poor conductors of heat, such that heat dissipation is a major issue. There would therefore be massive technological, environmental and societal benefits from the availability of commercially viable material systems that were excellent electrical insulators and good thermal conductors. Although it is intuitively appealing to think that thermal conductivity can be increased by adding a good thermal conductor to a thermally insulating material, this is not generally true, because the resulting boundaries give rise to phonon scattering which, effectively, offsets the anticipated gains. While this can be overcome if the thermally conducting additives form percolating paths through the material, the consequences of this have inevitably been an unacceptable reduction in the electrical breakdown strength of the material. However, recent results obtained at the University of Southampton appear to overthrow this paradigm. Specifically, a 20% INCREASE in breakdown strength has been accompanied by a 60% INCREASE in thermal conductivity in a system based upon hexagonal boron nitride (h-BN) dispersed in a polyethylene matrix. Since these preliminary results were obtained from a totally non-optimised system, we believe that further improvements in both technical performance and economic attractiveness (i.e. reduced cost from adding less h-BN) are attainable.The results of our preliminary work are contrary to accepted understanding, so the PROJECT AIM is to determine how simultaneous improvement can be optimised for use in two key materials that are particularly relevant to power cable applications. The key challenges are: to understand how to optimse the exfoliation of h-BN particles into their constituent layers and, subsequently, to disperse them within the matrix, such that the required combination of electrical and thermal characteristics result; to ensure scale-ability, such that laboratory results are technologically viable. In this project, we will consider two matrix systems, due to their technological relevance. First, we will examine crosslinked polyethylene (XLPE), since this is currently the most important cable insulation material. The work programme will progressively build from improving solvent dispersion, polymer blending methods and surface functionalisation, to scale-up with masterbatch production through combined solution and melt-process methods. Characterisation of the microstructure and dielectric testing will ensure consistent dispersion and distribution of the hBN filler, as well as optimal electrical properties. In this way, quantitative structure-property-process relationships will be established that will enable the resulting material systems to be used reliably in the electrical cable industry. While the focus of this project is on electrical properties, the knowledge about structure-property-process relationships will affect much wider technology areas, which employ advanced materials for improved mechanical or thermal properties.