The effect of thermal ageing on the electrical characteristics of insulating oil for pole transformers

This paper describes the electrical characteristics of insulating oil employed in pole transformers. In the experiment, temperature and frequency were selected as variables, and dielectric characteristic values such as the relative permittivity, the tandelta and the specific resistance of the insulating oil were measured by a WinDETA system. As a result, the dielectric characteristics of the testing objects were temperature and frequency-dependent, and especially, the relative permittivities of each object showed considerable difference. In addition, the specific resistance acted as a key factor determining the insulating performance, and it was rather frequency dependent than temperature dependent. And, the dielectric values measured before ageing was slightly different from those after ageing. Dielectric dispersion due to the space charge polarization was observed in all testing objects.