Effect of aging on the dielectric properties of insulation paper of power transformers

The aging of high-voltage equipment used in electrical networks is being studied with a view to minimizing the risk of damage and managing the replacement of outdated equipment. The majority of power transformers were built in the 1960s and 70s and are now reaching the end of their useful life. They will need to be replaced in the coming years. The life span of high-power transformers is dependent on the life span of their solid insulation, the paper enveloping the internal windings. Non-destructive methods have been developed for testing this insulation in recent years including the dielectric measurement method. Studies have shown that dielectric measurements are a function of humidity, temperature and the degree of aging of the paper/oil insulation system of transformers. The main objective of this study was to separate the contribution of paper aging and oil aging to the dielectric response. To separate the oil aging effects from paper aging effects, the dielectric response was studied on winding samples. The measurements on paper samples showed that there is no correlation between dielectric measurements and the degree of polymerization, which depends on the degree of aging of the paper. The measurement variations are related more to oil aging.