Calculation of the cyclic and emergency current rating of cables. Part 1: Cyclic rating factor for cables up to and including 18/30(36)kV
|Publication Date:||1 January 1985|
|ICS Code (Cables):||29.060.20|
No account has been taken at present of possible effects of moisture migration on the thermal resistivity of the soil. This is in line with the approach already adopted for the calculation of steadystate ratings in uniform soil as given in IEC Publication 287: Calculation of the Continuous Current Rating of Cables (100% Load Factor). Methods for dealing with regions having different thermal characteristics and with drying out of the soil are under consideration.
The methods in this standard apply to cables buried in uniform soil, either directly or in ducts, when carrying a load which varies cyclically over a 24 h period, the shape of each daily cycle being substantially the same. It is assumed that the voltage has been applied for a sufficiently long time for the conductor temperature rise due to dielectric loss to have reached a steady state. The total temperature rise of the conductor above ambient is then the sum of the steady-state temperature rise due to the dielectric loss (as given by IEC Publication 287) and the transient temperature variations due to changes of current.