Space charge development measurements inside oil impregnated pressboard

Electrification due to oil flow inside transformers induces charge accumulation at the pressboard interface. A part of this charge migrates inside the impregnated pressboard, which leads to a space charge development inside the pressboard. Then this accumulation may be responsible of electrical failure. In order to predict the phenomenon it is important to know the charge evolution and its variation with the temperature gradient and concentration of additives, considered to be used to prevent such failures. An experimental setup has been perfected in which an impregnated pressboard stack is submitted to a potential difference and a temperature gradient. From measurements of potential on special electrodes inserted in the pressboard stack it is possible to obtain the space charge density development. We have made experiments for several potential difference and temperature gradient. The evolution of the space charge density development is observed in terms of time. Then the effect of the Benzotriazol (BTA) concentration has been tested.