Degradation of dodecylbenzene under conditions of high electric field

Although extruded dielectrics are becoming increasingly important in the area of high voltage cables, the degradation of paper/oil systems is still of interest, in connection with both new installations and life prediction of ageing cables. The phenomena involved in the electrical degradation of such cables are still poorly understood. One of the difficulties associated with this problem is that none of the properties can be measured in situ, which requires the cable to be taken out of service. In addition any correlation of with extent of age in cables can only be ascertained for cables with known history (of loading) and manufacture. Recent studies of dielectric failure in cables have tended to focus on solid dielectrics. A number of models have been proposed to account for degradation in such systems. For fluid dielectric materials, more recent studies are backed up by a wealth of earlier studies. It would seem that from a chemical point of view the degradation processes occur via the formation and subsequent reaction of free radicals, or more strictly radical ions. In view of the suspected involvement of free radicals in the ageing process of dielectric materials, an understanding of the radical chemistry of the appropriate substrates is of some importance. Thus parallels have been drawn between the failure of dielectric materials and the chemical changes induced by high-energy ionising radiation. The principle changes that occur under irradiation are the result of interactions between ions, molecules, radicals and excited species formed in the system. Such changes include gas evolution (side chain scissions), combination to give higher molecular weight molecules, polymerisation, molecular degradation or dis-linking, and the formation of unsaturated materials. In this preliminary account of our investigations, both high-energy electron irradiation and high voltages have been used to degrade dodecylbenzene. The possible similarity between these processes was to be investigated through a study of the products formed by each method. In this way it was intended to gain a better understanding of the ageing of these dielectric materials.