Some considerations regarding the installed environment of under-ground power cables

Cable ampacity issues have been dealt with for a long time and our own involvement, in large part to provide information of local relevance to the cable industry and power companies in Finland, is quite recent. Nevertheless, in investigating the local environmental conditions of underground HV and MV cables, a number of practical issues worth stressing have come up. Further, in acknowledgement of the difficulty in knowing the actual thermal conditions of a cable at any given point in time, a simple temperature monitoring system has been devised, based on on-line current and cable surface temperature measurements. This monitoring system involves a simple transient algorithm that enables quite accurate prediction of the conductor temperature. The conductor temperature corresponds to the maximum temperature of the insulation, and is therefore the critical parameter in determining the current rating of a power cable.