The effect of temperature and field strength on the resistivity of transformer oil

Safety operation of total ultra-HVDC transmission system could be directly affected by the operation reliability of converter transformer which is one of the most important equipments in the system. The transformer oil is the main liquid dielectric medium in the converter transformer. Thus, it is significant to study the dielectric properties of the transformer oil. In this paper, the dc resistivity of transformer oil under different conditions has been systematically investigated, and then the temperature and field strength were the test parameter variables. The variation range of temperature was 25~80°C, and under each temperature point the field strength changed ranging from 0.5V/mm to 10kV/mm. Meanwhile, 15 min is selected as the duration of testing resistivity. In this paper, the authors obtained the systematical data points and analysis curves of resistivity under different temperature and field strength, and obtained a empirical equation which describe the relationship between resistivity, temperature and field strength. It enhanced the understanding of the resistivity for transformer oil and provided the theoretical and test basis to expand the engineering application of this transformer oil.