ECS Intranet:
Impact of Seabed Properties on Ampacity and Reliability of Cables

HV subsea cables are frequently laid in trenches at the seabed and buried within local seabed materials, with little consideration of the thermal regime they will either enter or generate. The changing nature of the burial environment will have significant implications for cable performance; the thermal rating of these cables is limited by the ability to balance their heat generation from electrical losses with transfer to the surroundings. Excessive temperatures distort the electric field in DC cable and prematurely degrade insulation and other components leading to early failure. The stability of the installed cable is dependent on the geotechnical properties of the seabed and these may change significantly both during installation and post-installation operation. With the external cable temperatures approaching 60°C or higher, the host seawater-saturated sediments will endure thermal conditions at 1 to 2 m depth typically only experienced following ~2 to 3 km of burial at normal geothermal gradients. In the short term this could result in porewater convection and subsequent reduction of bed shear stresses and hence the erodibility of the burial material whilst in the medium to long term they could promote diagenetic reactions between the sediment and porewaters such as mineral recrystallization, significant compaction, and partial induration. This project will utilise existing and new field data for HV cable routes (high resolution seismic, core logs and attendant geotechnical measurements, CPT information and direct time series of thermal measurements) to understand spatial and temporal variability of the pre- and post-installation physical environment along cable routes on the UK shelf.

Partners

• National Grid

Funding

• EPSRC
• National Grid plc

Principal Investigators

• sgs
• jp2

Other Investigators

• Justin Dix
• Tim Henstock
• Tom Gernon