The IEC standard 60287-1-1 describes methods to calculate the armour loss factor but does so for one layer of armour only. Other ampacity calculation programs allow the user to model as well only one layer. This poses a certain problem to correctly calculate the losses of a cable with two armour layers such as submarine cables or certain three-core cables. In addition, Cableizer offers some further improvements in calculating armour losses as compared to its competitors or the IEC standard.
Posted 2015-11-20
Categories: New feature, Theory, User guides
The IEC standard 60287-1-1 describes methods to consider non-magnetic and magnetic armour or reinforcement and calculate the armour loss factor $λ_2$ with some simplifications.
The method in the IEC standard only describes one layer of armour, for example round steel wires. To model cables with two armour layers, one can try to adjust the diameter of the armour wires to reach the same resistance as for the two layers combined. Not only is this a hassle, it results in a false diameter of the jacket and therefore in a false value of its thermal resistance $T_3$ as well as in a deviation in the thermal resistance $T_4$ of the environment. However, there is no limitation to double the layer and do the calculations separately for each layer.
With Cableizer you can now define two separate layers of armour of the same type but with independent input values for:
The methods in the IEC standard to calculate the armour losses use several simplifications. Because Cableizer is not really limited in calculation power, some of these simplifications have been dropped.
Length of lay | Touching wires | $R_A$ acc. IEC | $R_A$ acc. Cableizer |
---|---|---|---|
very long | yes or no | 1.0 p.u. | 1.0 p.u. |
54° lay | yes or no | 2.0 p.u. | ca. 1.7 p.u. |
very short | no | infinite | large |
very short | yes | 2.0 p.u. | 2.0 p.u. |