Experimental study of thermal performance of the backfill material around underground power cable under steady and cyclic thermal loading

• Main Authors: Ahmad, Shahbaz, Rizvi, Zarghaam, Arsalan Khan, Mohammad, Ahmad, Jamal, Wuttke, Frank
• Format: Conference Proceeding
• Language: English
• Subjects: Large scale experiment; Modified backfill; Soil physics; Soil thermal conductivity; Underground power cables
• ISSN: 2214-7853; 2214-7853
• DOI: 10.1016/j.matpr.2019.06.404

An experimental program is conducted to investigate the response of a dry soil heated by a cylindrical heater. The motivation for the work comes from its application to underground power cables which are employed for low, medium and in future for the high voltage electricity transportation and distribution. Due to the Joule heating, the power cables generate heat that has to be dissipated through the surrounding soil to prevent melting of the insulation and keep the cable below thesafeoperating temperature levels. Heat generation also causes the migration of moisture from the vicinity of the cable and allowing the formation of a dry out zone. The dry out zone due to loss of moisture becomes less thermal conductive and starts to heat up the power cable even faster. To prevent the damage in the cable the Ampacity or the current carrying capacity of the cable is reduced. Therefore, in this study, we modified the backfill material around the cable based on Fuller modification to achieve maximum density in the dry state (critical state). A large-scale experimental device is set up and tests were performed to observe the change in the thermal behavior of the backfill. A 5 days heating and cooling cycles of 12 hours are performed on the sand and modified backfill material and later allowed to relax for two days. The heat relaxation time for different heating conditions has been studied to quantify the nature of the backfill material for different loading scenarios.