Electric behaviour of press board submitted to an oil flow electrification

Flow electrification phenomenon has been observed for a long time in the petroleum industry and generally electrostatic hazards have been avoided using additives. More recently the electrical industry has been concerned with the emergence of failures caused by flow electrification in power transformers, as in such transformers oil is used as well for insulation and to cool the system. A research program is developed jointly by E.D.F. (French Electricity) and our laboratory in order to understand the charge transfer between oil and press board. In this study we analyse the phenomenon in terms of the evolution of temperature. Indeed, it seems that the failures occur when the oil temperature is low and growing, especially after the transformer has not been in use for some time. Thus special equipment has been developed in order to measure the evolution of the wall current at the oil press board interface in terms of temperature, oil velocity and distance from the duct entrance. The results obtained show a special high dependence between the charge transfer and the temperature, when it is nearly constant in terms of distance to the entry and proportional to the oil velocity