Static electrification in power transformers: Correlation between charge generation and ECT-tan/spl delta/ parameters for different oil-pressboard couples

Up to now the ECT (Electrostatic Charging Tendency) measurement and, to a smaller extent, the continuous aging test for tan /spl delta/ are the most commonly applied measurements for transformer monitoring. So it is important that the reliability of these two tests involving only the oil should be established for different oil-pressboard couples. As part of the research program of Electricite de France in the field of static electrification in transformers, an experiment has been carried out, at the university of Poitiers, to study the most constrained parts in transformer as far as flow electrification is concerned: the insulated pressboards between windings. So, the generation process has been investigated with regard to time, temperature and velocity, for different oil samplings (used and new oils) flowing along a used or a new pressboard. In the meantime, ECT and tan /spl delta/ tests have been performed for each types of oil. It turns out that those two monitoring measurements and the charge generation in the pressboard are not always directly correlated but that diagnosis requires a deeper analysis taking into account transient kinetics aspects and pressboard state.