Thermal calculations for buried gas-insulated transmission lines (GIL) and XLPE-cable

The requirements of transmitting high amounts of electrical power with an underground transmission system will cause high performance in low system losses. A comparison between the XLPE-cable and the GIL for the same buried parameters shows that the operating temperature by cable is 1.5 to 2 times higher than those of the GIL. This study shows that the GIL meets this requirement better than the cable and is therefore the most reliable solution. A numerical study and long-term test measurements proved the accuracy of the computer code used for this study. The calculated values are verified with measurement carried out with a long duration test at the IPH Test Laboratory in Berlin, Germany. In this long duration test the GIL has been proven through accelerated ageing for an expected life time of 50 years.