Failures of medium voltage cable joints in relation to the ambient temperature

The failure occurrence of a typical resin cable joint used in the medium voltage cable network in the Netherlands shows to have a correlation with the ambient temperature. This behaviour is especially seen when the failures occurred during the summer months are considered. Especially in the years 2003 and 2006 high temperatures in the months July or August were recorded and the number of failures increased significantly in these months. This ambient temperature has an influence on the soil temperature through the year and can even have an effect on daily basis. It is observed that the failures follow the rise and fall of the average air temperature during the different days of the month with increasing and decreasing number of failures with some time delay. The change of the soil temperature around the joint results in a higher temperature within the joint, thus contributing to the failure of a joint, which is already in its ageing stage. The presence of a hotspot in combination with a rise of the soil temperature can result into breakdown.