Sulfur corrosion phenomena

Sulfur corrosion phenomena

Tests, treatment, and consequences – Q & A

Sulfur corrosion phenomenon that damages copper inside a power transformer is quite old since it was observed almost immediately after implementing mineral oils a hundred years ago

Sulfur corrosion phenomenon inside a power transformer is quite old since it was observed almost immediately after implementing mineral oils for insulating power transformers. The first papers on this subject appeared a hundred years ago [1]. The debate on how the sulfur in oil affects the copper inside transformers continues from that period on.

Sulfur is an abundant and important element that can be found in almost all natural materials on earth. It is the third most abundant element in the human body and all other living organisms. It appears in all crude oils since they originate from living organisms. Petroleum contains sulfur as well. According to [2], insulating oil contains a very large number of diverse organic sulphur sompounds even up to 20 %. The oil composition changes dramatically due to many different sophisticated processes, such as hydrogenation. Although there is early evidence of sulfur corrosion, it seems that th is subject has become more popular and discussed extensively since 2005. Most of the transformer users, insurance companies and experts were concerned about this issue in the last two decades. With the appearance of new standards, the main guides for oil tests were revised, and sulfur corrosion tests were shifted from unnecessary to compulsory routine ones.

Since it has become a popular subject within the last two decades, it is necessary to reconsider the importance of this phenomenon. At the beginning of this millennium, the literature described many failed transformers due to sulfur corrosion phenomena. However, in the last few years, much fewer cases of failure have been reported, and most of the literature mainly describes deep research on different aspects of this phenomena.

If the industry aims to approach this phenomenon correctly and finds the adequate remedy to reduce the distress from the sulfur issue, it is recommended to bring back the sulfur corrosion tests as part of the special section in the main transformer oil testing process. Otherwise, it remains a very important unsolved threat for most of the transformers around the world.

With the appearance of new standards, the main guides for oil tests were revised, and sulfur corrosion tests were shifted from unnecessary to compulsory routine ones

In this article, I will try to answer the most common questions asked by transformer users regarding their concerns on tests, interpretation, and remedies. The questions, which are examples of the problems the users face, are followed by concise answers and discussion that explains the rationale.