Research on Moisture Content Evaluation Method of Transformer Oil-paper Insulation Based on Low Frequency Non-linearity

Frequency domain spectroscopy (FDS) is widely used in insulation condition assessment of power equipment because of its unique advantages. However, due to factors such as differences in the insulation structure of actual transformers, there are still many problems in the field application. To tackle this problem, this research proposes a new characteristic parameter, by measuring the degree of non-linearity
$\gamma$
between the voltage and current of the samples, to reflect the moisture content of the oil-paper insulation in the transformer. The results show that
$y$
under 0.01 Hz voltage excitation better reflects changes in moisture, and the fitting relation is given. The composite insulation structure models with different structures were also tested, and it was found that the FDS curve was greatly affected by the insulation structure, while
$\gamma$
was not. Therefore, it can be a more efficient method to evaluate the moisture content of the transformer main insulation.