Sustainable Power Cable Materials Technologies with Improved Whole Life Performance

Current extruded polymeric cable materials technologies are based on crosslinked polyethylene and, consequently, suffer from two major problems. Polyethylene melts at a relatively low temperature (~90 to 110C) and therefore crosslinking is employed to give improved thermomechanical stability. However, this only results in a safe maximum working temperature of ~95C, whilst rendering the material extremely difficult to recycle at the end of the cable's life. These factors limit cable circuit performance and create problems once the asset has reached the end of it's useful life. Addressing these problems is particularly timely due to the growing medium voltage (MV) and high voltage (HV) power utility markets in the UK and worldwide. This demand is driven by the imperitive to replace existing aged HVAC systems, to provide new power system connections to renewable generation sources in the developed world (particularly HVDC) and for infrastructure development in developing countries. In HV systems there is also a need to operate cables at higher peak loads within a flexiable AC transmission system (FACTS) framework.This proposal will remove current performance and recyclability limitations by developing a new generation of low-loss recyclable materials with high-temperature operational capabilities, evaluating their performance in cable designs and by developing and applying a whole-life assessment tool to quantify the operational/economic/environmental/sustainability benefits. The result will be improved network performance through a technology that is fundamentally recyclable as well as creating new materials that have global market development potential. The problem will be addressed by a consortium that includes a major polymer supplier, a major utility company, a University partner and a SME research provider. The project will be coordinated by National Grid with technical project management support supplied by Gnosys. Materials development will be jointly undertaken by Southampton University, GnoSys and Dow. Dow will supply materials and model cables and Southampton will undertake electrical/physical testing of them. Gnosys will provide additional materials support and the whole life assesment tool and, with National Grid, apply it to cable case studies. The following methodology will be adopted, in order to meet the project objectives. Programme 1A. A detailed review of alternative materials technologies will be initially undertaken to define best candidate materials for new high performance polymeric HV and MV cable insulation systems. Programme 1B. From the results of Phase 1, thermoplastic polymer blends with high electric strength, high thermal stabilty and good flexibility will be developed to enable the cable insulation to operate continuously at limits of 140 to 150C; that is, 50 to 60C higher than present insulation systems.Programme 1C. Ease of extrusion during manufacture and ease of reprocessing at end of life to facilitate recycling are essential requirements. Model cables will then be fabricated and assessed with respect to thermo-mechanical stability, cable flexibility, dielectric loss, enhanced electrical breakdown and voltage endurance behaviour, and ease of processing. Programme 2A. A whole life performance-economic-environmental cable model will be constructed using the newly developed LEETS methodology and software tool, appropriately modified to determine the overall sustainability performance and the benefits of the new generation materials benchmarked against existing materials. The model will explore optimum solutions for several cable designs taking into account network operational needs.Programme 2B. The selected candidate materials will then be subjected to whole-life operational, economic and environmental assessment within MV and HV cable designs informed by new cable rating and system studies linked to the LEETS tool.