Research on Reduction Method for Dielectric Dissipation of Transformer Oil-Paper Insulation at Low Temperature

In extremely cold regions, the dynamic viscosity concerning the transformer oil in the oil-immersed transformer will change in winter. The dielectric properties of the transformer's main insulation at low temperatures are significantly different from those at normal temperatures. As it is inevitable to carry out dielectric properties testing about transformers at low temperatures during the handover test of winter in some areas, it is very important to carry out research about the state assessment of oil-paper insulation at low temperatures. In existing standards, the reduction method for the oil-immersed power transformers’ dielectric dissipation factor does not consider the influence of insulation aging and the content of moisture. What's more, the reduction results at low temperatures have large deviations. In view of the above, this paper proposed the power frequency dielectric dissipation factor's equivalent reduction method concerning the transformer's main insulation at low temperatures, which is based on FDS test data concerning oil-paper insulation obtained under laboratory conditions in the wide temperature range. This method is combined with the equivalent model of dielectric relaxation for the transformer's main insulation and considers the content of moisture and the aging of insulation. It provides an important theoretical basis for the accurate evaluation of insulation state transformers.