Static electrification of the insulating materials used in power transformers

It is shown that the electrostatic charge tendency (ECT) is a precious indication allowing to evaluate the levels of the charge density which can be reached by oil in a power transformer. A correlation can be made between this parameter (ECT) and the physicochemical and electrical characteristics of the oil. It is shown that the water migration phenomena at the oil/pressboard interface play an important role in the charge separation. So, we investigate the influence of the rugosity of the pressboard, the temperature gradients and the ageing of the oil. The effect of the antistatic additives on the ageing and the ECT is also considered.