In this thesis the lifetime assessment of low-pressure oil-filled (LPOF) cables is investigated. Most of the LPOF cables are already quite old but it is unknown if the degradation of these cables matches the age of the cable. Due to energy transition and the fact that not all cables can be replaced simultaneously, an estimate of the lifetime of the cable needs to be defined. This is done in this research using the following three research questions:
• What is the health level of the LPOF cables based on their historical loading profiles and their health index?
• Which LPOF cables are suitable for more loading?
• What is the remaining lifetime of cables that are suitable for more loading on this new loading levels?

These questions are answered using a thermal ageing model based on the historical loading data. From this model it could be concluded that the thermal degradation of the insulation of TenneT’s LPOF cables has been very limited even after 50 years of service. This means that it might be possible cable insulation wise to let it be run continuously on the nominal loading level (maximum allowed temperature) for another 47 years. Although it must be mentioned that the accessories remaining lifetime and loading capabilities are not investigated in this research.

There are done tan delta measurements on an old cable to see if there would be any degradation visible from the 50 years of ageing of the cable. From this testing there was no noticeable degradation in the insulation paper visible. However, from this testing it could not be fully conclude that no ageing would be visible from this cable. Therefore, more testing needs to be done which could be done in the following way.