This paper presents the results of design, manufacturing, testing and validation of a medium and low voltage cable which has been blocked against the ingress of water and gas potentially occurring at water depths up to 3500 meters. Offshore umbilical and deepwater applications are considered.
The power cable consists of a longitudinally blocked, stranded conductor which is surrounded by an insulating core of semi-conducting and insulating layers thereof. The conductor has an effective blocking system that includes strand seal compound or a combination with water swellable elements. For a given stranded conductor configuration, various blocking components were systematically studied using a specially modified manufacturing process developed to enforce a copper conductor that is able to provide satisfactory performance in the field and during the next manufacturing process stages.
The result was a cable core capable of passing a longitudinal water penetration test at 400 Bar according to the conditions expected on the seabed at 3500 meters. This characteristic, provides a safety power cable for use in harsh, demanding applications, and is designed to allow a repair even during the unlikely event of external damage of the cable jacket that can be caused by fishing, extreme environmental conditions or heavy objects dropped from the surface. In addition, the electrical performance of the cable was verified following industry accepted cable standards, in tests such as partial discharge, step voltage and conductor resistance.
Finally, the development of the new blocking system ensures that a power cable for water depths up to 3500 meters is able to support up to 400 bar of longitudinal pressure. The cable was successfully tested according to an umbilical cable validation protocol.
