“Corrosive sulphur from sulphur combustion by-products (C3)” is the criticality characterised by the corrosive property of oil, and other insulating liquids, with respect to the metallic surfaces of which some components (e. g. copper conductors or silver contacts) inside transformers and other electrical equipment are made. This criticality is specifically caused by sulfur combustion by-products such as H2S (hydrogen sulfide), mercaptans, elemental sulfur, and so on, originated by oil regeneration treatments that use thermal re-activation of fuller’s earth (or other particulate matter) by combustion.
Corrosive sulfur – Free sulfur and corrosive sulfur compounds detected by subjecting metals such as copper ti contact with an insulating liquid under standardized conditions [from IEC 62697-1 of 2012, par. 3. 1. 6 – page 10]
