High voltage submarine cable

Abstract: A high voltage submarine cable, the cable (10) comprising principally two as such conventional cable cores (12, 13) arranged side by side thereby providing a flat cable, each core (12, 13) comprising a conductor (14) and a conductor screen (15) surrounded by an insulation (16) with an insulation screen (17) and further a lead sheath (18) as well as a steel tape reinforcement (19), the two cores (12, 13) being bundled together by a tape bedding (22) thereby also enclosing suitable filling (20), a cross tape armouring (22) of galvanized steel tapes being wound around the two cores (12, 13), surrounded by at least one layer of a transversal reinforcement (23) saturated with asphaltic compound.

Description: The present invention is related to a high voltage submarine power cable. High voltage director current cables are used on land and in submarine environments and using a central insulated conductor and the seawater as such for the return current. Such known cable causes an external magnetic field and the sea electrodes may produce toxic chlorinated compounds, which means environmetal problems. It therefore is desirable to develop a cable system without such environmental problems, and especially a high voltage submarine power cable for shallow water with low magnetic field. A flat cable with an outer armour consisting of metal armour overwrap is known from US 4 600 805, describing also that a special wrap of galvanized steel is utilized, however, without specifying the wrap as such. A cable structure comprising an outer armour consisting of two layers wound in opposite direction is known from DE 945 857, Each layer consists of two metal tapes wound in such a way that the second tape overlap the gap between the consecutive turns of the first tape. Basic claims to cables of the above type includes requirements connected with handling and spooling the cable onboard a vessel offshore. Basically it is important that the position of the two cable cores in relation to each other is maintained accurately to avoid any kind of electrical disturbance when during operation. Therefor there should be no differential movement between the two cores which could accumulate and cause kinks, bird cages and so on. To ensure against this all bending should be around the cable long axis, i.e. around the common centre axis fro the two cores. In case the cable is to be twisted, this should be done around the centre axis, i.e. around the touching point of the two cores. Furthermore the travelled distance for the two cores shall be identical. In case it is necessary to bend the cable around the short axis it is better to let the cable twist around it's centre until the previous requirement is fulfilled. The above requirements is fulfilled with a cable having a very high bending resistance on it's short axis whereas the bending resistance on the long axis should be low, which requires high friction between the two cores and between the cores and the bonding preventing the cores gliding along each other. In relation to prior art cables, the high voltage submarine power cable according to the present invention provides a cable construction having low magnetic field and fulfilles the above requirements. This is achieved with the cable according to the present invention as defined by the features stated in the claims. In the drawing figure 1 discloses a transversal section of the cable according to the invention and figure 2 discloses more detailed the individual layers in figure 1. The cable according to the present invention comprises principally, as disclosed in figure 1, two as such conventional cable cores 1 arranged side by side thereby providing a flat cable 10. The cores may be produced with any insulation type for DC voltage. If necessary, it may be reinforced and armoured to sustain radial and/or longitudinal mechanical stresses, A cross tape armouring 2 of galvanized steel tapes is wound around the flat cable, hollow spaces preferably being filled with an internal filler material 3. Alternatively a thick tape capable to contain hot asphaltic compound is to be wound around the cores as first layer. The steel tape(s), if required, are to be thoroughly coated with asphaltic compound to ascertain the life requirement of the cable, The tape has to have outer serving of PP-yarn impregnated with asphaltic compound 5. Suitably, a fiber optical cable 4 may be embedded in the internal filler material 3. The steel tapes 2 may suitably have a width of for example 90 mm and be wound at around in a 45° angle two and two tapes 2 side by side. It is also preferred that the steel tapes 2 are wound in twins in both directions. The more detailed figure 2 discloses the tape armoured 2-phase power cable 10 according to the present invention in a cross section, comprising the two phases or cores 12 and 13. Each of the cores 12 and 13 comprises a conductor 14 with a conductor screen 15, mass impregnated insulation material 16 with an insulation screen 17 as well as a lead sheath 18 and an outer transversal steel tape reinforcement 19. These layers are saturated with asphaltic compound. Layers of high friction tapes 27 may also be provided around each core. The two cable cores 12 and 13 are bundled together with suitable filling material 20 and optional elements, such as a fiber optic cable 21, by a tape bedding 22, one or more layers of transversal reinforcements such as steel tape 23, saturated with asphaltic compound, an optional bedding 24, optional steel wire armour 25 and corrosion protection 26. Said steel tape 23 preferably having opposite lay to the tapes 19 around the cores. The bonding steel tapes 19 and 23 provide high pressure between the cores thereby preventing gliding between the cores and rolling of the cores on each other as such movements would require deformation of the steel tapes. The high pressure between the cores and the steel tapes also prevent mutual axial gliding of the two cores.

Claims: A high voltage submarine cable, the cable (10) comprising principally two as such conventional cable cores (12, 13) arranged side by side thereby providing a flat cable, characterized in each core (12, 13) comprising a conductor (14) and a conductor screen (15) surrounded by an insulation (16) with an insulation screen (17) and further a lead sheath (18) as well as a steel tape reinforcement (19), the two cores (12, 13) being bundled together by a tape bedding (22) thereby also enclosing an internal filles material (20), a cross tape armouring (22) of galvanized steel tapes being wound around the two cores (12, 13), surrounded by at least one layer of a transversal reinforcement (23) saturated with asphaltic compound. Cable according to claim 1, characterized in the transversal reinforcement being a steel tape (23). Cable according to the preceding claims, characterized in a bedding (24), a steel wire armour (25) and a corrosion protection (26) surrounding the transversal reinforcement (23). Cable according to the preceding claims, characterized in the cable comprising an optic fibre cable (4) embedded in the internal filler material (20). Cable according to the preceding claims, characterized in a thick tape capable of containing hot asphaltic compound being wound around the cores (12, 13) as a first layer. Cable according to the preceding claims, characterized in the steel tape(s) being coated with asphaltic compound.

Inventors: BALOG GEORG, BJERKE BJORN, ERIKSSON KARL GEORG, BALOG, GEORG, BJERKE, BJORN, ERIKSSON, KARL GEORG
Applicants: NEXANS
Application year: 2001
Main classification: H01B7
IPC codes: H01B7