Aging of 154 kV underground power cable insulation under combined thermal and electrical stresses

Subterranean power cables insulations are degraded due to the combined thermal and electrical stresses it is experiencing. Such insulation are further degraded by the fact that they must carry enough current to transmit electricity at long distances without losing power but at the same time must not reach a critical temperature due to electricity. It's degradation is due to environment variables such as excess temperature, external radiation, humidity and defects in manufacturing such as voids, contamination and mechanical defects. XLPE cables are currently used for high voltage cables as an insulation material. The main source of thermal stress for transmission cables is from resistive heating of the conductor and this heat propagating through the insulation. The losses related to load current arise in conductor and metallic sheath, while the dielectric losses are generated in the insulation. In terms of specification, ampacity is the maximum temperature that the cable insulation can withstand over a long period without serious degradation. Another major factor is caused by electrical stresses. Electrical insulations loss their useful life to to irreversible changes taking place in their chemical composition and physical properties. However, the development of models used to calculate electrical and thermal stresses can be used to determining the stresses that insulation cables are experiencing. The model can be used for all types of XLPE insulation material.