Degradation and Cupric Corrosion caused by Corrosive Sulfur in Insulating Oil

Abstract

Refining method of insulating oil was changed from acid-refining to hydro-refining in the 1970's. And addtion of benzotriazole (BTA) in insulating oil was recognized in Japanese Industrial Standard in 1988. These changes are preferable to suppression of oxidative degradation and cupric corrosion phenomena caused by corrosive sulfur.
We have studied oxidative degradation and cupric corrosion caused by corrosive sulfur.
It is known that tanδ changes like N-character pattern in process of oxidative degradation.
The maximum value of tanδ is proportional to amount of soluting copper, sulfur contents and inversely contents of aromatic compound in the insulating oil.
The amount of corrosive sulfur in the insulating oil is at small level recently, but cupric corrosion caused by corrosive sulfur increases with amount of oxigen in the insulating oil.
Cupric corrosion caused by corrosive sulfur is related to soluting copper and sulfuric ion in the insulating oil, therefore degree of cupric corrosion could be measured by soluting copper and sulfuric ion.
We found that BTA is effective for both prevention of oxidative degradation and cupric corrosion caused by corrosive sulfur in the insulating oil.