Recent progress in the characterization of conduction losses in dielectric liquids

The authors first give a general presentation of the problem of the characterization of conduction in insulating liquids. Then they briefly describe the low field conduction phenomena in liquids and the linear model for conduction losses. The conditions for a correct determination of the resistivity are presented and the extremely important role played by the transit time of ions is pointed out. They describe the new method based on the measurement of the initial current following the application of a voltage step and an improvement of this method based on the application of a succession of alternate positive and negative voltage steps. The method recently led to a new IEC standard - which is briefly presented - and to new instruments for the characterization of highly insulating liquids the potential of which is pointed out.