Investigation of Thermal Boundary Conditions During Heat Cycle Tests on HVDC Cables

The number of installed high voltage direct current cables is steadily increasing. The electric field distribution in HVDC cables is determined by the electrical conductivity. The temperature distribution is therefore a field-determining factor, since the electrical conductivity of the insulating medium is strongly dependent on the temperature. The temperature distribution can be calculated using analytical or numerical models on the one hand and determined experimentally using heat cycle tests on full-scale cables on the other hand. In order to control the thermal boundary conditions of cables exposed to the air during test procedure, the cables are often covered with thermally stable flexible elastomeric foam. The question arises to what extent the thermal conditions of the cables buried in the soil can be reproduced by using the flexible elastomeric foam during heat cycle tests. For this reason, this publication compares the temperature distribution in buried cables with those in foam-covered cables and describes the impact of the use of flexible elastomeric foam on the temperature profile in the cable.