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in electrical networks is being studied with a view to minimizing the risk of damage and managing the replacement of outdated equipment.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.
Since a few years, non-destructive techniques for assessment of power transformer insulation systems have been developed. The dielectric response in time and frequency domain is studied to determine the oil/paper insulation condition. One of the important parameters affecting the dielectric response is the temperature.On real transformer, the temperature of measurement is not controlled and is usually related to ambient temperature, therefore in order to compare measurements at different temperature it is important to study the influence of this parameter..It is well know that the temperature dependency to the response of transformer insulation follows an Arrhenius type law and that it is possible to normalize to a master curve measurement taken at different temperature. To evaluate this dependency and to model it, this study was done on transformer model with both the dielectric response in time and frequency domain with the temperature varying from 10 to 50 'C. The results allow us to model the dependency of the temperature and to calculate the activation energy.
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