Redefining Transformer Operating Requirements: A Temperature Based Approach toMitigate Silver Sulphide

Recent transformer failures have highlighted the growing importance of silver sulphide formation on on-load tap changer (OLTC) selector switch contacts as a distinct and critical degradation mechanism. While corrosive sulphur in transformer oils has historically been associated with copper sulphide formation in windings, several recent incidents demonstrate that silver-plated selector contacts are also vulnerable under certain chemical, thermal, and operational conditions. This paper investigates the mechanisms governing silver sulphide formation and proposes a temperature based risk assessment framework to support condition assessment.