MVAC Submarine cable, magnetic fields measurements and analysis

The recent concerns for the environment have caused an increase in the number of offshore wind farms. These farms use submarine cables to transmit the power onshore. Recent studies show that the cables are being over-dimensioned when using the standard formulas for their design, given by the IEC Standard 60287. Researchers believe that the wire armour of three phased submarine cables is the reason for the inaccurate calculations by the standard. Studies show that the magnetic behaviour of these cables are changed due to the wire armour. In order to investigate this hypothesis, this paper intends to supply the theoretical research with data from magnetic field measurements on a wire armoured 3-phase submarine cable, together with an investigation of the induced currents in the different cable components. The influence of the physical arrangement of the armour wires on the electric behaviour is also investigated, since several researchers believe that the twisting of the armour wires result in zero net induced voltage over one helix length. This is shown to be valid for the tested cable. Finally a replica of the armour has been built with just a single conductor in the centre. This setup was used to measure how the magnetic field varies between wires, above a wire, inside the wire arrangement and at sections without armour. The magnetic field tests are compared to a COMSOL model of the specified cable showing good compliance between experimental and simulated results. It is concluded that at low core currents, the magnetic field is not a dominant factor to the results and the behaviour of a wire armour and pipe armour is similar.