Corrosive and non-corrosive sulfur in transformer oils

Corrosive sulfur in the insulating fluid in electrical equipment should be absent or at a level considered not detrimental to the metallic components, particularly copper conductors and braces. Total sulfur analysis of several transformer oils reveals that the sulfur is organic and not corrosive. Levels as high as 2000 ppm are detected. The most corrosive form of sulfur is elemental sulfur itself, active even at low ppm levels. The best method of assessing corrosive sulfur is by the copper corrosion test specified in ASTM D1275.