Cooling of Buried Power Cables by Using Metallic Pipes as an Alternative to Polymeric Pipes - Comparison of Results from Experiments and Simulations
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- Institutt for elkraftteknikk 
It is common to install power cables in polymeric pipes at road crossings and in urban areas where exceptional protection and flexibility is necessary. In such case, the pipe is usually filled with air, which increases the thermal resistance to the ambient surroundings, thus leading to a higher conductor temperature compared to if the cable was installed directly in soil. As a consequence, the current carrying capacity of the cable is limited by the high temperature inside the pipe, leading to a poor utilization of the cable. This thesis has emphasized whether a metallic pipe can lower the operating conductor temperature of a power cable when compared to a polymeric pipe, due to the low thermal resistance of metals. To investigate this hypotheses, a laboratory experiment was conducted with a duration of approximately 3 months. Three different models were constructed, each with its own design of cable installation. These included direct burial in soil, installation in a buried polymeric pipe and installation in a buried aluminum pipe. A three phase cable was installed in series through each model, which was energized with three variac-controlled transformers. In addition, the experiment was simulated by the help of finite element software, and both results were analysed and compared to each other. The main finding from the experiment was a lower conductor temperature inside the aluminum pipe compared to the polymeric pipe, and that the lowest operating temperature solely occurred in direct installation in soil. The simulations suggested a much higher temperature deviation between the two pipes compared to the results from the experiment. It was found that the models were too short, leading to a large amount of longitudinal heat transportation which was difficult to analytically compensate for in the simulations. Despite deviations between the experiment and simulations, aluminum pipes seems to have a great potential regarding natural cooling of cables, thus increasing the cables current carrying capacity.