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This paper investigates the impact of sulphur contamination, specifically Di-Benzo-Di-Sulfide (DBDS), on the insulation behavior of model transformers during partial discharge (PD) activity. The objective is to understand how reactive and corrosive sulphur affects the copper conductors and subsequently the insulating paper-oil systems within transformers. The methodology employed involved online measurements of the dissipation factor (tanδ) and PD activities on paper-covered copper conductors under sulphur contamination. Results demonstrate that the presence of corrosive sulphur leads to the formation of semi-conductive copper sulfide, which adversely affects the insulating paper by promoting partial discharge activities and degrading insulation resistance. These findings underscore the critical role of monitoring tanδ and PD in assessing transformer insulation integrity, revealing that high levels of DBDS sulphur in transformer oil can significantly compromise insulation reliability and increase the likelihood of premature transformer failures. The research contributes valuable insights for the power industry to enhance transformer maintenance strategies and improve overall reliability by mitigating the effects of sulphur in insulating materials.