Study and experimental evaluation of the effects of ambient quantities on the operation of medium voltage cable joint

In this work, the effects of humidity, pressure and temperature on medium voltage cable joints are analysed through a literature review and experimental evaluation. This thesis is realized in collaboration with A2A. At first, a brief description of cable joints is given, highlighting the reasons for their weakness. These are handmade in the worksite, with all the dust and dirt, and are a source of interfaces, where defects are more common and more critical. A literature review follows. Humidity inside the joint leads to metal rust and water trees, reducing its lifespan. Externally, moisture favours the heat dissipation reducing the thermal resistivity of the soil. Instead, a high interfacial pressure inside the joint reduces the risk of water ingress, as well as the losses of the insulation, while outside the pressure applied by sharp objects may damage the joint. Regarding temperature, it is expected to be one of the causes of increased water ingress due to higher thermal movement, as well as increased interfacial pressure due to thermal expansion, while it also encourages partial discharges initiation. Externally, a high ambient temperature accelerates the drying of the soil, discouraging the heat exchange. Finally, experimental results from laboratory tests are presented. Two medium voltage cable joints, equipped with sensors for pressure, humidity and temperature, were subjected to thermal cycles. In both joints, humidity decreases as temperature increases, and the temperatures follow that of the climatic chamber. Also, the mean pressure increases due to consecutive thermal cycles, in both devices. However, the pressure profile is different: in the one called A it decreases as temperature increases, while the opposite occurs in joint B. Moreover, a possible correlation can be defined between the joints and ambient humidity, even if few test were performed on this topic.