Calculation of the Cyclic and Emergency Current Rating of Cables Part 3: Cyclic Rating Factor for Cables of all Voltages, with Partial Drying of the Soil
|Publication Date:||1 February 2002|
|ICS Code (Cables):||29.060.20|
This part of IEC 60853 gives a method for calculating the cyclic rating factor, for cables of all voltages, where partial drying out of the surrounding soil is anticipated. The method is based on one of the three methods published in a CIGRE1 document. The method is applicable to any type of cable, but it is recommended that it should be applied only to installations of one multi-core cable or to three single-core cables or to groups of circuits where the intercircuit spacing is sufficient to permit free vertical movement of soil moisture between the zones of dry soil associated with each circuit. This standard does not preclude the use of other methods of calculation where full details of the load cycle are not known.
The method assumes that the entire region surrounding a cable or cables has uniform thermal characteristics prior to drying out; the only non-uniformity being that caused by drying. As a consequence the method should not be applied, without further consideration, to installations where special backfills, having properties different from the site soil, are used.
1 Methods for calculating cyclic ratings for buried cables with partial drying out of the surrounding soil: Electra No 145, December 1992, page 32.