Effects of metal deactivator concentration upon the gassing characteristics of transformer oils

Recent years have witnessed a relatively large number of power transformer and shunt reactor failures, which were attributed to the presence of corrosive sulfur compounds in the insulating oils and their attending reactions with copper to form electrically conductive copper sulphides. The associated problems appeared to be initially resolved by the addition to the insulating oil small amounts of a metal deactivator (more commonly called passivator), a derivative of 1,2,3 benzotriazole (BTA). However, over the past four years, additional problems arose that were principally associated with the evolution of gases from the electrical insulating oils, containing the metal deactivator. These observations, recorded in the field as well as reproduced in laboratories, are examined in this paper.