17 Jun 2025
Expert Oil Diagnostic Services
What is Corrosive Sulfur?
Corrosive sulfur refers to certain reactive sulfur compounds in transformer oil that can chemically attack metal components, especially copper and silver. These compounds can form metal sulfides, which are often conductive and can lead to insulation failure. This issue has been recognized for decades, with early reports dating back to 1948.
What is The Impact to Transformer?
Corrosive sulfur can lead to the formation of copper sulfide on transformer windings and silver sulfide on selector switch which compromises the insulation and can cause electrical failures. The extent of the damage depends on the concentration of reactive sulfur compounds and the operating conditions of the transformer.
How to Detect Corrosive Sulfur?
ASTM D1275B : Standard Test Method for Corrosive Sulfur in Electrical Insulating Liquids
IEC 62535 : Insulating liquids - Test method for detection of potentially corrosive sulphur in used and unused insulating oil
DIN 51353 : Testing of insulating oils - Detection of corrosive sulfur - Silver strip test
How to mitigate the effect of corrosive sulfur?
Oil Replacement
Putting metal passivator
Oil’s Chemical Treatment
Copper Corrosive Phenomenon
Silver Corrosive Phenomenon
For more info on our insulating oil analysis services, please don't hesitate to contact our team members:
Shaily Hatun Mohamed Saleh (shaily.hatun@tnb.com.my)
Muhammad Hadi Ahmad Fauzi (hadi.fauzi@tnb.com.my)
Roshaniza Ismail (roshaniza.ismail@tnb.com.my)
Nur Syahida Akryl Azam (nursyahida.azam@tnb.com.my)