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

世界面临着一项重大挑战，即如何可靠、经济地向不断增长的人口供应能源，而不造成严重的环境破坏。展望未来，我们对电力的依赖将不可避免地增加，因为交通和供暖越来越电气化，而这一增长将主要由可再生能源来满足。这些设施将建在条件适宜的地方，在英国，一个例子是开发北海主要海上风力资源的计划。然而，大型海上设施的建设和由此产生的电力传回岸上仍然非常昂贵，因此，必须有效地完成这一任务。所有的发电厂都依赖于电绝缘，今天，这主要是基于聚合物。虽然这些材料是优秀的电绝缘体，但它们也是热的不良导体，因此散热是一个主要问题。因此，商业上可行的材料系统将带来巨大的技术、环境和社会效益，这些材料系统是优秀的电绝缘体和良好的导热体。虽然直观地认为可以通过在隔热材料中添加良好的热导体来增加热导率，但这通常是不正确的，因为所产生的边界会引起声子散射，从而有效地抵消预期的增益。虽然如果导热添加剂在材料中形成渗透路径，这是可以克服的，但其后果不可避免地是材料的电击穿强度的不可接受的降低。然而，最近在南安普顿大学获得的结果似乎推翻了这种范式。具体来说，在分散在聚乙烯基体中的六方氮化硼（h-BN）体系中，击穿强度增加20%的同时，导热系数增加60%。由于这些初步结果是从一个完全非优化的系统中获得的，我们相信在技术性能和经济吸引力方面的进一步改进（即通过添加更少的h-BN降低成本）是可以实现的。我们初步工作的结果与公认的理解相反，因此项目目标是确定如何同时改进，以优化与电力电缆应用特别相关的两种关键材料的使用。关键的挑战是：了解如何优化h-BN颗粒在其组成层中的剥落，并随后将其分散在基体中，从而获得所需的电学和热特性组合；确保可规模性，使实验室结果在技术上可行。在这个项目中，由于它们的技术相关性，我们将考虑两个矩阵系统。首先，我们将检查交联聚乙烯（XLPE），因为这是目前最重要的电缆绝缘材料。工作计划将逐步从改善溶剂分散、聚合物混合方法和表面功能化，到通过结合溶液和熔融工艺方法扩大母粒生产规模。表征微观结构和介电测试将确保一致的分散和分布的hBN填料，以及最佳的电性能。通过这种方式，将建立定量的结构-性能-过程关系，从而使所得到的材料系统能够可靠地用于电缆行业。虽然该项目的重点是电性能，但有关结构-性能-工艺关系的知识将影响更广泛的技术领域，这些领域将采用先进材料来改善机械或热性能。

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.