Medium voltage joint design options for higher conductor temperature (110 °C)

A new special polypropylene insulation (PP-insulation) for medium voltage cables (MV-cables) permits a permanent conductor temperature of 110 °C for cables in continuous operation. However, connectors and accessories are only tested an approved for a conductor temperature of 90 °C. To ensure a long lifetime of the connectors and the insulating part of the joints, the connection areas should be designed as a kind of a heat sink. Using MV-cables with different conductor cross-sections (95 mm2, 300 mm2) and materials (aluminium (Al) or copper (Cu)), it is shown how such a heat sink can be designed. The intention is to limit the temperature in the connection area of the joint to 90°C, while the temperature of the conductor of the PP-insulated medium-voltage cable, which is not thermally affected by the joint, can reach 110°C. The ampacity of these MV-cables with PP-insulation is compared with cables made of cross-linked polyethylene (XLPE) insulation. The investigations were conducted using calculations with a thermal model based on the Thermal Network Method (TNM) on a single cable joint arrangement. Different ambient temperatures of air and soil conditions were taken into account.