Analytical expression of equivalent transverse magnetic permeability for three-core wire armoured submarine cables

As three-core wire-armoured submarine cables become progressively more relevant, the need for refined modelling techniques grows likewise. IEC Standard 60287 indications though are still widely recognized to be insufficiently accurate, since several effects due to the presence of the collective wire armour are ignored. This paper therefore offers an insight into the induced losses mechanism as a function of the armour wires electromagnetic properties. The analysis is focused on the influence of the armour transverse permeability, whose overall resultant value is estimated by means of a simplified yet effective formulation. Such analytical approach is tested in a 2D FEM environment in terms of power losses distribution and compared both to the IEC indications and to an existing formula in the literature. It is found that the values of permeability proposed by the IEC Standard underestimate the induced sheath power losses due to the presence of the armour, whereas the proposed approach improves the accuracy, as the magnetic flux density enhancement within the cable is accounted for.