Influence of ambient temperature on the failure behavior of cable joints

The failure behavior of resin cable joints in the medium voltage underground network in the Netherlands shows a correlation with the ambient temperature of the air above the ground. This behavior is especially seen when the failures occurred during the summer months are considered. In the last years the months July or August were very hot and the number of failures increased significantly in these months. The ambient temperature has an influence on the soil temperature through the year even 0.5 -1 meter below surface level where most cables are installed. It can also be seen 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. In this paper the failure behavior of resin cable joints and the possible effect of ambient temperature are discussed.