Condition monitoring of vegetable oil insulation in in-service power transformers: some data spanning 10 years

Abstract

Power transformers are expected to operate for several decades [1]. The insulating oil of a power transformer can be replaced if it becomes too degraded. However, it is obviously financially preferable to a utility that the insulating oil last as long as practically possible. Vegetable oils were among some of the earliest types of dielectric liquid, e.g., a team led by George Westinghouse used caster and linseed oils from the late 1880s onward [2]. However, a disadvantage was that the vegetable oils readily oxidized, and so mineral oils were adopted. In the mid to late 1990s there was renewed interest in vegetable oil-based dielectrics, to which antioxidants had been added [3]. Subsequently, vegetable oil-based transformer oils became commercially available. Initially, they were used only in smaller distribution transformers. However, as the electrical industry became more confident, they began to be used in ever larger power transformers from the early 2000s.