Ageing behavior of dodecylbenzene/mineral oil blends

Despite the continuing growth of polymeric insulation systems, paper and oil are still routinely used in many items of high voltage plant as the dielectric material. In such systems the oil provides a convenient medium for sampling in order to indicate plant condition. However, in order to understand the ageing of oils in plant, and more importantly, to predict the remaining lifetime, requires controlled laboratory ageing experiments. Previous investigations into the ageing behaviour of dodecylbenzene under a range of ageing conditions have shown that the oils darken on ageing with a corresponding increase in dielectric loss. On ageing with copper, a characteristic absorbance at 680 nm ("red absorbers") correlated to a catastrophic increase in dielectric loss. Whilst this is a useful diagnostic indicator, this destructive reaction would quickly lead to plant failure. Ways of eliminating such problems are required if dodecylbenzene is to be used successfully in high voltage insulation systems. This paper provides a novel solution to the problem -mixtures of DDB and mineral oil.