Performance of the +or-250 kV HVDC Skagerrak submarine cables. Further development of the HVDC paper-insulated, mass-impregnated (solid type) submarine cable

A review is given of the performance of the +or-250 kV HVDC mass-impregnated, solid-type submarine cables installed between Denmark and Norway. The cables, which have been partly overloaded, have successfully met all requirements. Three mechanical failures have occurred, two due to heavy beam trawls and the third during stormy weather. On two occasions the cables were repaired in stormy weather. They have been hit by a great number of trawlboards and fisherboats' anchors without any significant damage. Tests and investigations of the insulation have demonstrated that this type of cable can be used for far higher voltages than assumed before. Migration of the impregnant is of less significance than previously believed. The cable can tolerate very high mechanical strains, such as those arising during layering at very great sea depths. Bending tests were made on cable pieces at tensions up to 72 metric tons; the results of the subsequent electrical tests were excellent, and no visible traces of damage of the insulation were found. The design stresses are considered, and suggestions are made for the design of cable for very deep waters. >