High Voltage Cables – A Technology Step

Abstract A two-sided marked push for subsea power transmission has taken place in the last 5 years, first initiated by the oil & gas industry's push for subsea electrification, then followed by a desire to reduce the CO2 footprint from oil & gas production throughelectrification of production facilities with power from onshore. More recently, the dramatic development in offshore wind and especially the floating wind market for clean renewable power results in the same need. Common for both areas is the need for transmission capability of the electric power at high voltage. Subsea cables for high voltage have existed since the early 20th century, but deep water and dynamic use of cables has, until recently, only been needed in niche areas. The know-how and experience from the niche areas combined with long-term operational experience for high voltage transmission cables has been a vital factor leading to the development of a qualified solution for deepwater and/or long-distance cabling system which also function in a dynamic situation. The latter is vital for larger offshore wind farms, as well as subsea development. Electrical insulation systems are grouped as wet or dry, where the latter traditionally has been used for voltage ratings above 52 kV. The traditional solution using lead as a water barrier is not suited for dynamic applications and this paper presents the process of qualifying a new industrial solution for dynamic high voltage cables suited for deep water and/or harsh weather for oil & gas or floating windfarms. A complete 145 kV dry design cable system has been qualified for dynamic and static use, with factory joints and repair joints making deepwater and/or long-distance transmission capacity possible. At the same time, qualification of a 72.5 kV wet design cable and factory joint has been completed. The qualified transmission system consists of a mixture of traditional cable design and a new novel water barrier system for subsea cables. Combining this development with the extended qualification of wet design supports increased power transmission capacity.