Impact of corrosive sulfur in transformer insulation paper

In recent years a significant volume of research has been undertaken in order to understand the latest failures in oil insulated power apparatus due to deposition of copper sulfide on the conductors and in the insulation paper. Dibenzyl Disulfide (DBDS) has been found to be the leading corrosive sulfur compound in the insulation oil. As there are currently no nondestructive techniques available to analyze the degree of damage from sulfur corrosion, electrical plant operators are faced with a choice of either replacing an asset which might still have several years of operational life or keeping a transformer operational with an increased risk of failure. This paper investigates permittivity and loss factor curves of transformer oil impregnated insulation paper, at different corrosive sulfur degradation stages. Three types of transformer conductors are investigated; new, artificially aged and service aged. To increase the understanding of the electrical behavior of Cu₂S this paper demonstrates how the electrical properties change with moisture content. Dielectric spectroscopy is used to demonstrate some of the electrical changes across a wide frequency range, from 1mHz to 1MHz.