Comparison of parameters in the formation of corrosive sulphide deposition on copper conductors

Copper is a catalyst that promotes the formation of corrosive sulphur but it is also corroded by the latter. Corrosive sulfur in oil has been identified as the cause of recent failures in power transformers and shunt reactors. The most common reason of such failures is arcing between adjacent disks or conductors of windings due to the formation of copper sulphide deposition on cellulosic insulating paper. Synergetic effects with temperature, time and oxygen are recognized to play a role in the formation of corrosive sulphur. Which of these factors has the most impact on copper sulphide deposition? To address this concern, a quantitative laboratory technique has been developed. It is shown that by using a series of laboratory experiments in accordance with ASTM D 1275 B, it is possible to investigate this problem and to map the influence of these parameters by manipulating some variables such as oxygen, temperature and time on the copper samples. The obtained results show that temperature is the most influential parameter in the formation of corrosive sulphur. The process is accelerated when both temperature and time act conjointly.