Estimation of Moisture Content in Oil-impregnated Pressboard through Analyzing Dielectric Response Current under Switching Impulse

This paper proposes an advanced technique for estimating the paper moisture content within oil-impregnated pressboard by analyzing its dielectric response current signature under switching impulse voltage. The present work is oriented towards development of a method which can assess the condition of transformer insulation through measuring the dielectric response current during its switching on or off operation to the grid. In order to investigate the effectiveness of the method, the dielectric response current of a few oil-impregnated pressboards containing different moisture contents, are measured using switching impulse in laboratory. Based on the applied switching impulse and corresponding response current, the branch parameters of the equivalent circuit of insulation are evaluated which have been employed for formulating its transfer function. The zero and pole calculated from the transfer function are found to be sensitive to the paper moisture of insulation. Correlation of transfer function zero and pole with the paper moisture of insulation are derived using the experimental results. These correlations are validated through the experimental investigation on few other test samples.