On the stability of mineral insulating oils under electrical stress

There is a general agreement that in service conditions the quality of mineral insulating oils gradually deteriorates under the impact of electrical, thermal and chemical stress. It is also widely accepted that only the incipient electrical failures such as hot spots and partial discharges are responsible for the gassing of oil. Nevertheless, the relationship between the cause and the symptoms of paper insulation deterioration is not clearly understood. This article intends to show that the gassing of oil is a more complex phenomenon. It provides experimental evidence that the chemical composition of hydrocarbon blend and the oil born decay products are also contributing factors to oil gassing.