Influence of copper on gassing properties of transformer insulating liquids

During the last 10-15 years, there has been an increasingly growing number of reports on the so-called stray gassing of mineral insulating oils. Some contributions suggested that the problem may be connected with introducing new types of insulating oils [1] and mainly associated with evolution of hydrogen, as also confirmed by transformer oil producers [2]. Oil passivation has also been reported to contribute to stray gassing, being used as a remedy for sulfur corrosion problems [3]. We exclude from further consideration gassing due to material incompatibilities, e.g., outgassing of paints, cross-linked polyethylene (XLPE) or other materials, as it remains the transformer manufacturer's duty to develop test methods for avoiding this problem.