Reliability of eco-friendly cables in future power grids

With the green energy transition and massive electrification of society, energy consumption in Norway is expected to increase significantly. Grid capacity is a limiting factor for development of new industry, renewable energy production and consumption, therefore major grid investments are required. Due to future demands in a circular economy power cables with insulation based on polypropylene thermoplastics (PP-TP) may be considered as an eco-friendly alternative to cables with cross-linked polyethylene (XLPE) which are installed today. PP-TP cables require less energy and have lower CO2 emissions during manufacturing, and have shorter lead time. XLPE cables were introduced in the Norwegian distribution grid during the 1970s. This first-generation design suffered from many unexpected failures after only 10–15 years in service due to a degradation mechanism called water trees. Up to now, XLPE has been the only electrical insulation system approved by the Norwegian standard NEK HD 620 S2. This standard is currently under revision, allowing the use of PP-TP. However, limited service experience is available and more knowledge is required to map which factors that represents a threat to the service life-time of PP-TP cables. REWARD will assess properties that are relevant for AC cables in the medium (MV) and high voltage (HV) grid (12-145 kV), but also provide fundamental knowledge for applications at higher (EHV) voltage ratings (=145 kV). REWARD will address major knowledge and technology gaps prior to large-scale installation of eco-friendly PP-TP cables in the Nordic grids and in future high voltage subsea applications for renewable energy. • Electrical long- and short-term performance of mechanically stressed insulation systems. • The effect of artificial contaminations on electrical pre-breakdown mechanisms. • Performance in wet environment and reliable insulation analysis. • Lifetime assessment methods for designs exposed to Nordic climate and grid transients.

With the green energy transition and massive electrification of society, energy consumption in Norway is expected to increase from 140 TWh today, to 178 TWh in 2030. Grid capacity is a limiting factor for development of new industry and renewable energy production, and grid investments of 160–200 billion NOK in the period 2021–2030 are announced. This includes both new installations and reinvestments of cables approaching end of life, as well as 10 billion NOK allocated to offshore grids. Power cables with cross-linked polyethylene (XLPE) insulation was introduced in the Norwegian distribution grid during the 1970s. This first-generation design suffered from unexpected failures after only 10-15 years in service. Up to now XLPE has been the only electrical insulation system approved by the Norwegian standard NEK HD 620 S2. The standard is currently under revision, allowing the use of thermoplastic cable insulation materials based on polypropylene compounds (PPC). PPC cables are recyclable, require less energy and have lower CO2 emissions during manufacturing, thus being an eco-friendly alternative to XLPE. However, limited service experience is available, especially in colder climate, and there are significant knowledge and technology gaps that need to be addressed prior to large-scale installation of PPC cables: • Electrical long- and short-term performance during and after mechanical stress is unknown • Effect of contaminations on electrical pre-breakdown mechanisms is not examined • Performance in wet environment is not understood, and reliable analysis methods are not established • Lack of lifetime assessment methods for designs exposed to Nordic climate and grid transients The REWARD project will aim to provide this knowledge to ensure safe and reliable use of eco-friendly cable designs in the Nordic grids and future high voltage subsea applications, hence avoiding unexpected premature service failures as experienced for the first XLPE cable generation.