For the UK to meet legally binding renewable targets by year 2020 and beyond, a series of wind farms are under construction, and more new projects are being developed. The offshore grids and their connection to the existing transmission systems can only be realised using the HVDC links. Using high voltage will make power transmission more efficient and the only feasible solution is to use extreme upgrades to existing plant. Cables, the key part of the HVDC links, will be forced to operate well beyond their existing limits (currently about +/-500 kV and 1000 MW). This means that both cable insulation and operating conditions have to be pushed far beyond the limits currently considered acceptable. Therefore, a fundamental understanding of the performance of the insulation and the development of novel operating methodologies are urgently required to meet the challenges. This project will investigate the impact of inherent defects, space charge dynamics, partial discharges, electrical tree and power quality on electrical performance of highly stressed lapped cable insulation and develop novel operating methodologies that take account of the influence of the above factors to achieve reliable and safe operation for the HVDC links.