University of Tabriz Tabriz Journal of Electrical Engineering 2008-7799 49 3 2019 12 01 Lifetime Estimation of Oil-Impregnated Transformers based on Degree of Polymerization Lifetime Estimation of Oil-Impregnated Transformers based on Degree of Polymerization 995 1006 9660 FA M. Ariannik Faculty of Electrical Engineering, K.N. Toosi University of Technology, Tehran, Iran A. A. Razi-Kazemi Faculty of Electrical Engineering, K.N. Toosi University of Technology, Tehran, Iran Journal Article 2017 05 29 Nowadays, reliability of power system is of great importance. Therefore, the condition of transformers as the expensive and critical components of a power system have to be monitored and assessed. The dominant factor that causes limitation in transformers lifetime is the paper insulation. The influence of moisture, oxygen and temperature that affect the paper insulation have been investigated in this thesis. Degree of polymerization (DP) is the indirect measurable criterion used for assessing paper insulation. With consideration of the calculated hot-spot temperature of transformer in hourly steps along with an annual linear growth rate for the water content, the lifetime of transformer has been estimated with regards to DP criterion for three couple of ambient temperatures and load factors. The resultant lifetimes are in agreement with real lifetime of the transformers. This lifetime estimation has been conducted for Kraft paper and thermally upgraded Kraft paper and lifetime of these two paper types are compared under various operating and environmental conditions. Finally, considering the obtained DP profiles, the optimum time for implementing moisture reduction in the paper insulation has been studied and discussed in form of three scenarios. Nowadays, reliability of power system is of great importance. Therefore, the condition of transformers as the expensive and critical components of a power system have to be monitored and assessed. The dominant factor that causes limitation in transformers lifetime is the paper insulation. The influence of moisture, oxygen and temperature that affect the paper insulation have been investigated in this thesis. Degree of polymerization (DP) is the indirect measurable criterion used for assessing paper insulation. With consideration of the calculated hot-spot temperature of transformer in hourly steps along with an annual linear growth rate for the water content, the lifetime of transformer has been estimated with regards to DP criterion for three couple of ambient temperatures and load factors. The resultant lifetimes are in agreement with real lifetime of the transformers. This lifetime estimation has been conducted for Kraft paper and thermally upgraded Kraft paper and lifetime of these two paper types are compared under various operating and environmental conditions. Finally, considering the obtained DP profiles, the optimum time for implementing moisture reduction in the paper insulation has been studied and discussed in form of three scenarios. https://tjee.tabrizu.ac.ir/article_9660_21f8e4935a83f3b0621763d1593bdd77.pdf