This article explains how to calculate the current rating of cables in J-tubes. Typically J-tubes are the thermal bottleneck of submarine power cable routes.

A new calculation method based on FEM and IEC 60287 for current rating of HV cables in soils with multiple different thermal resistivities is explained with an example calculation. Modelling the different soil thermal resistivity zones (multiple backfills) is important for obtaining accurate cable current ratings.

The methods for calculating the current rating of multiple cables installed in ventilated tunnels are explained with example calculations. Overall tunnel length and air velocity inside the tunnel have a significant impact on cable current ratings.

The calculation of current ratings for groups of (multiple) cable circuits require the quantification of the mutual heating component between the groups of circuits. This example is for multiple groups of circuits in air on the same cable ladder. This article will discuss the IEC 60287 approach.

A report investigated 6214 cable failures over a 14 year period. The main causes were insulation breakdown, excavation, joints or switchgear failure. The results may surprise you.

Charging current in power cables is 10-20 times larger than for overhead lines. The maximum length of cable circuits is determined by their capacitance. This report provides equations and shows how critical cable length depends on voltage level, cable size and frequency.

The effects on the current rating of cables buried in soils with different thermal resistivities are examined with software using the finite element technique.

The definition of emergency rating is the permissible short-term rating of a cable already loaded and at a steady-state, considering the thermal capacitances and the thermal resistances of an installed cable system. The definition of cyclic rating is the maximum current of a cable when the load is varied in a sequence of steps that are repeated cyclically. The cyclic rating differs for different sequences and different cycle periods. Both emergency and cyclic ratings deal with time-varying loads

This article explains why dynamic ratings are important when dealing with long AC cables for wind farms. An example calculation of a dynamic rating which uses the measured load profile is given.