IEC 60287 often overrates shallow-buried cable ampacity. ELEK’s method models soil surface cooling for safer, more reliable HV cable ratings.

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

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.

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.