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

Lead Research Organisation: University of Southampton
Department Name: Electronics and Computer Science

Abstract

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.

Planned Impact

Economic: This project will bring economic benefits to both developed and developing economies. In Europe, some 1.5 Mton per annum of polymeric materials are used for electrical insulation, with an estimated value of ~£2bn. The "UK Renewable Energy Roadmap" published in 2013 indicates that DECC recorded announcements of private sector investment in renewable generation worth £31bn between January 2010 and September 2013, with the potential to support over 35,000 jobs. According to DECC's April 2014 "Energy Investment Report", the pipeline of UK energy sector investment projects is worth £218bn; thousands of associated supply-chain jobs are being produced across the UK. The 2014 "IEA Renewables Report" indicates a similar position worldwide, with global investment of around $250bn in new renewable power capacity in 2014 alone. We therefore believe that the technology that results from this work will lead to increased global sales of UK manufactured advanced materials and high technology equipment and, consequently, will enhance the provision of UK high technology jobs. The Sub-Saharan Africa (SSA) power outlook, as conducted by KPMG in 2016, estimates a short-term increase of ~70 GW in the need for electricity and that investments of $120bn to $160bn are required, per annum, in order to provide electricity access to the entire Sub-Saharan region by 2030. Cross border projects, as exemplified by the MoZiSa and ZiZaBoNa transmission schemes, are needed to significantly upgrade the regional transmission network between the respective countries. Several energy initiatives amongst ASEAN countries show
the increased momentum towards enhancing and expanding interconnections throughout the region. There has been particular interest in tapping the hydropower potential in Cambodia, Lao PDR and Myanmar for domestic use and cross-border interconnections, to supply growing demand in Thailand, Malaysia, Singapore and Viet Nam, as a means of facilitating trade and underpinning dlopment of a regional power market. For example, Lao PDR more than quadrupled electricity exports from 2.8 TWh in 2000 to 12.5 TWh in 2013 and expects to quadruple again by 2025.

Social and Environmental: The provision of improved cable systems for the efficient connection of renewable resources to national networks and for the interconnection of neighbouring power systems will bring social and environmental benefits to both developing and developed economies. This includes contributing to the provision of electricity access the entire Sub-Saharan region through increased access to energy, by optimising the exploitation of renewable generation resources and realising more affordable tariffs. This will, then, lead to more reliably energy supply to the population and subsequently provide the basis for improved water management and supply, and drive improved social, agricultural and industrial development, as part of primary infrastructure development. Similar benefits are expected in South East Asia, with the growth of hydropower, wind and solar-based renewables. In UK, the technology developed in this project will help the UK government to meet its post-2020 cost target of <£100/MWh, and will grow UK on- and offshore wind energy employment (currently 18,300 and 17,100 employees respectively). We anticipate the development of the Custom Material Supply chain by GnoSys will help protect >3,000 jobs in the UK electronics, automotive and aerospace industries, where optimised high performance materials are crucial for competitiveness. HM government has estimated that UK materials-related industries have a yearly turnover of £197bn. The result of this project will be integrated into the University of Southampton's EPSRC funded public engagement activities activities (POLYMAT EP/N002199/1), which include Café Scientifique lectures, school visits and supporting web-based materials that demonstrate the societal benefits that stem from materials and energy research.

Publications

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Description Traditionally, any changes to an electrical insulation material, which improve its thermal properties will diminish the ability to withstand electrical fields. This follows the logic that what anything that is a good thermal conductor (e.g. metals) is also a good electrical conductor. The objective of this feasibility study was to find out if simultaneous improvement of electrical and thermal ratings can be achieved and optimised reliably for the use in power cable applications. This was achieved by using hexagonal boron nitride platelets of nanometric scale, which have improved thermal conductivity by virtue of their material properties, but also helped the ability to withstand electrical breakdown due to their barrier properties. This improvement has been shown to be reliable and repeatable, not only for conventional XLPE as currently used in power cables, but also in polypropylene based insulation for the next generation of power cables. The optimal combination of electrical and thermal properties was found to be achieved at a boron nitride fillgrade of just 2 % by weight. Additionally, the DC resistance was also found to be reduced, which further helps high voltage DC systems, which are vital to transmit power from renewables in remote locations to our city centres.
Exploitation Route The findings of this feasibility study can be taken forward by cable manufacturers and are of particular use for HVDC cable systems that connect renewables like offshore wind platforms with the grid. The next step will be the use of these materials that have been shown to work on laboratory scale in medium voltage or minicables. The simultaneous improvement of electrical and thermal properties is not limited to be used in power cables, but can also find use in aerospace electronics or power electronics, where the ability to transfer heat away while retaining high dielectric strength would be beneficial. Furthermore, the increase in dielectric breakdown strength due to the barrier properties of boron nitride can lead to reduction of polymers used for insulation, achieving higher energy densities where weight or space restrictions are an issue.
Sectors Aerospace, Defence and Marine,Electronics,Energy

 
Description LS Cable & Systems Ltd. 
Organisation LS Cable & System
Country Korea, Republic of 
Sector Private 
PI Contribution Our research team provided information on thermoplastic, recyclable alternatives to conventional cable insulation systems. While LS Cable & Systems has been investigating alternatives to conventional PE- and EVA- based cable systems in the past, they do not have the facilities and testing equipment to drive material design and characterisation. The project partners GnoSys and University of Southampton have the expertise and testing facilities to quickly and efficiently assess the feasibility of a number of candidate polymers, nanoscale fillers and additives, which would take LS Cable & Systems years to build.
Collaborator Contribution LS Cable & Systems is one of the largest cable manufacturers worldwide and based in Korea, with power as well as telecommunications cables as core business, along with integrated modules and accessories. They also provide engineering services including installation, testing and commissioning of both land based and submarine cable systems. As such they are able to give valuable industrial input on the applicability of the designed systems. While they were involved with the feasibility study of the materials themselves, the collaboration with LS Cable & Systems will be vital for the project going forward, now that the feasibility study was successful. LS Cable & Systems is able to produce both scale versions of power cables as a proof of concept, as well as full-scale prototype cables with the new materials designed as part of the project. Since LS Cable & System has a large market share in developing countries, this will be an avenue to ensure the benefits of this new technology will end up in the markets where they are most needed.
Impact LS was able to provide respectively confirm specifications for polymers to be used with current extrusion technologies, so that new materials designs can rapidly be implemented into products that benefit end users, without the need of completely new production facilities.
Start Year 2017
 
Description IEEE WG 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact The PI presented current research work at the IEEE Working Group on Nanodielectrics, which is an expert panel consisting of members of industry and academia that meets bi-annually, usually at international conferences in the field of solid dielectrics and phenomena. In 2017 the WG met at the Electrical Insulation Conference (EIC) in Baltimore on the 11th of June 2017. The panel was initially skeptical about the use of nanofiller in cable systems, since previous work with MMT and silica did not result in tangible benefits. A number of panel members were convinced based on the quality of presented data and a number of panel members were reaching out after the discussion with further input or follow up questions. The result was increased awareness of the potential of hexagonal boron nitride as candidate for dielectrics.
Year(s) Of Engagement Activity 2017
URL https://www.ieee.org/conferences_events/conferences/conferencedetails/index.html?Conf_ID=37787
 
Description Nagoya University 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact The PI was invited to the Electrical Engineering department of Nagoya University and presented the idea behind and some results of the ongoing feasibility study for use of PP based insulation with hBN nanometric filler material for power cables with flexible rating. Participants were mostly postgraduate students and academics in related fields, who asked a number of questions on how these new materials might affect the power grid as a whole, especially related to increased use of renewables like solar and wind, that might have generation peaks that with conventionally rated cables suffer from curtailment. It was outlined how the increased thermal overhead can offer more flexibility when connecting large scale renewables, and how these new materials benefit a more sustainable future, by not only allowing more renewable power generation, but also being recyclable materials instead of non-recyclable insulation materials used in today's conventional cables.
Year(s) Of Engagement Activity 2017
URL https://www.nuee.nagoya-u.ac.jp/index-e.php
 
Description Rushlight 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact The whole event is focused on a celebration and promotion of cleantech innovation. Incorporating the Innovate UK Energy Catalyst Round 4 Showcase and the Rushlight Cleantech Innovation Showcase; the latest innovation and developments at the tip of the resource hierarchy in the Resourceful Conference; the latest market-ready sustainable solutions for corporate customers; all the latest developments and announcements from BEIS on UK Energy strategy and the largest cleantech exhibition in the heart of London, this event combines all that is the latest in energy, cleantech and sustainability. GnoSys and the University of Southampton participated at the Innovation Showcase and could raise awareness for the limitations of current cable technology when a further increase of renewable power generation is promoted, and promoted the outcomes of the feasibility study as a potential solution to these challenges.
Year(s) Of Engagement Activity 2018
URL https://www.rushlightevents.com/rushlight-show/