Dry zone formation around underground power cables during load cycling may lead to thermal failure of the cable's insulation. This phenomenon has to be recorded to send an alarm to the maintenance crew when the soil around the cable reaches the critical value at which the dry zone has started to be formed. In this study, the buried cable thermal model is modified to include occurrences of dry band formation during dynamic loading. An algorithm has been proposed for corrections of the cable load cycle to maintain the insulation maximum temperature at 85°C and not exceed this limit. This is suggested for reducing the dry zone formation effect on the cable insulation lifetime. The study is done on different single-core cables using different soil samples that can be used as backfill materials. The variations in thermal soil resistivity and soil thermal capacitance with temperature and moisture content of backfill soil are considered. The practical system used for monitoring the dry zone formation around the cable has been proposed. |
