Electric power transmission cables containing a first portion provided with first armouring wires having a first tensile strength, the first armouring wires being made of a first metallic material coated with a first metallic protection coating with a thickness more than 100 g/m.sup.2, the first metallic material having a first magnetic permeability 1, a second portion provided with second armouring wires having a second tensile strength, the second armouring wires being made of a second metallic material coated with a second metallic protection coating with a thickness more than 100 g/m.sup.2, the second metallic material having a second magnetic permeability 2, and 21, the first armouring wires being longitudinally joined to the second armouring wires at a joint, the joint having a third tensile strength that is at least more than 80% of the lower tensile strength of the first tensile strength and the second tensile strength.

Electric power transmission cables containing a first portion provided with first armouring wires having a first tensile strength, the first armouring wires being made of a first metallic material coated with a first metallic protection coating with a thickness more than 100 g/m.sup.2, the first metallic material having a first magnetic permeability 1, a second portion provided with second armouring wires having a second tensile strength, the second armouring wires being made of a second metallic material coated with a second metallic protection coating with a thickness more than 100 g/m.sup.2, the second metallic material having a second magnetic permeability 2, and 21, the first armouring wires being longitudinally joined to the second armouring wires at a joint, the joint having a third tensile strength that is at least more than 80% of the lower tensile strength of the first tensile strength and the second tensile strength.

Provided is a power cable, particularly, an ultra-high voltage underground or submarine cable for long-distance direct-current transmission. More specifically, the present invention relates to a power cable, in which an insulating layer has high dielectric strength, an electric field applied to the insulating layer is effectively reduced, and particularly, a void is suppressed from occurring in the insulating layer due to contraction of insulating oil, caused by a decrease of temperature in the insulating layer under a low-temperature condition or when the supply of an electric current is stopped, thereby effectively suppressing partial discharge, dielectric breakdown, etc. due to an electric field concentrated in the void.

Provided is a power cable, particularly, an ultra-high voltage underground or submarine cable for long-distance direct-current transmission. More specifically, the present invention relates to a power cable, in which an insulating layer has high dielectric strength, an electric field applied to the insulating layer is effectively reduced, and particularly, a void is suppressed from occurring in the insulating layer due to contraction of insulating oil, caused by a decrease of temperature in the insulating layer under a low-temperature condition or when the supply of an electric current is stopped, thereby effectively suppressing partial discharge, dielectric breakdown, etc. due to an electric field concentrated in the void.

A system comprises a trunk submarine cable, an offshore optical and power switching unit connected to the trunk submarine cable, and a plurality of feeder submarine cables connected to the offshore switching unit. The offshore switching unit is configured to dynamically connect data communication channels of a selected feeder submarine cable among the plurality of feeder submarine cables with data communication channels of the trunk submarine cable.

A system comprises a trunk submarine cable, an offshore optical and power switching unit connected to the trunk submarine cable, and a plurality of feeder submarine cables connected to the offshore switching unit. The offshore switching unit is configured to dynamically connect data communication channels of a selected feeder submarine cable among the plurality of feeder submarine cables with data communication channels of the trunk submarine cable.

Provided is a power cable, particularly, an ultra-high voltage underground or submarine cable for long-distance direct-current transmission. More specifically, the present invention relates to a power cable, in which an insulating layer has high dielectric strength, an electric field applied to the insulating layer is effectively reduced, and particularly, a large void is suppressed from occurring in the insulating layer when the power cable is left at low temperatures for a long time until electric current is supplied thereto after installed in a low-temperature environment, thereby effectively preventing partial discharge, dielectric breakdown, etc. from occurring due to an electric field concentrated in the large void.

Provided is a power cable, particularly, an ultra-high voltage underground or submarine cable for long-distance direct-current transmission. More specifically, the present invention relates to a power cable, in which an insulating layer has high dielectric strength, an electric field applied to the insulating layer is effectively reduced, and particularly, a large void is suppressed from occurring in the insulating layer when the power cable is left at low temperatures for a long time until electric current is supplied thereto after installed in a low-temperature environment, thereby effectively preventing partial discharge, dielectric breakdown, etc. from occurring due to an electric field concentrated in the large void.

A cable is used, in particular, as an underwater cable and contains a central element, which is surrounded by a cable sheath. The cable sheath has an inner hydrophobic sheath layer made of a first plastic and an outer sheath layer applied to same and made of a different plastic to the inner sheath layer. A polyolefin-type plastic is used for the inner sheath layer and one of the sheath layers, in particular the inner sheath layer is chemically functionalized, and a sealed connection is formed between the two sheath layers.

A cable is used, in particular, as an underwater cable and contains a central element, which is surrounded by a cable sheath. The cable sheath has an inner hydrophobic sheath layer made of a first plastic and an outer sheath layer applied to same and made of a different plastic to the inner sheath layer. A polyolefin-type plastic is used for the inner sheath layer and one of the sheath layers, in particular the inner sheath layer is chemically functionalized, and a sealed connection is formed between the two sheath layers.