Long term investigation of thermal behaviour of 110 kV underground transmission lines in the Belgrade area

摘要

The paper presents the most important results of investigations of the thermal behaviour of 110 kV underground transmission lines. Special attention was paid to investigating the thermal behaviour of critical hot spots in the cable routes where, during characteristic annual weather periods, the soil surrounding the 110 kV underground transmission lines undergoes a long term process of drying. By measuring different hot spots, it has been determined that, due to the effect of drying out of the soil, they constantly operate at temperatures of the cable surface which are several tens of Celsius degrees above the value for normally humid soil. The paper describes the procedure for applying a special cable backfill material, developed and manufactured at the Nikola Tesla Institute for the thermal stabilisation and reduction of hot spot cable operating temperature, on specific hot spots of 110 kV underground transmission lines in Belgrade area. Continued investigations of the thermal behaviour have confirmed that the correct use of the backfill material is a necessary and sufficient means for removing the negative effects of soil drying on the increase of the operating temperature of 110 kV underground transmission lines. The results presented in this paper are an important contribution to the proof of the justification and necessity of defining and introducing in practice new procedures for the thermal stabilisation and reduction of operating temperature of existing, as well as of new underground transmission cable lines to be built.