Experimental simulation of effects of high temperatures on paper oil insulation of transformers in presence of DBDS in mineral oil

The effect of elevated temperatures induced by over currents on the performance of paper oil insulation of transformer is investigated. This study has been carried out in presence of spiked concentrations of Dibenzyl disulphide (DBDS) in mineral oil for understanding its effects on copper sulphide formation. The dielectric response of paper oil insulation when subjected to elevated temperatures is studied using frequency domain spectroscopy and measurement of polarization and depolarization current. It is observed that there are significant variations in tan δ (dissipation factor) and magnitudes of polarization and depolarization currents of paper oil insulation due to high temperatures. A characteristic peak of tan δ around 0.1 Hz in the FDS response is observed to indicate the presence of copper sulphide on paper. A FEM based thermal model is proposed to explain the distribution of thermal conductivity and temperature gradient in paper oil insulation due to copper sulphide deposits.