On the role of temperature and impurities in the low field conduction of insulating liquids

The conductivity of several different transformer oils-pure or used or containing known concentrations of additives-was measured using the alternate square wave method in the temperature range 20/spl deg/C-90/spl deg/C. The conductivity ratio /spl sigma//sub 90/spl deg/C///spl sigma//sub 20/spl deg/C/ was found in the range 35-40 for pure oils and in the range 15-25 for pure oils with the addition of an ionic surfactant and for a used transformer oil. A discussion based on the Fuoss model (1958) is given. The results confirm the interest of measurements at room temperature to characterize the conductivity and dissipation factor of new and in service transformer oils.