Dielectric behaviour in non-pure dielectric liquid films

Abstract

The dielectric behaviour of silicone liquid with impurities has been investigated under sinusoidal or rectangular AC voltage. Measurements of the dielectric constant epsilon ' and the dissipation factor tan delta as a function of frequency (30-105 Hz), temperature (-60 degrees C to 50 degrees C) and field strength (5-50 kV cm-1) have been made for non-pure silicone liquid films of thickness several microns. A well-defined tan delta peak appears at a low frequency range, and tan delta depends upon the field strength. When the frequency of applied AC voltage is suddenly changed to a lower or higher frequency, epsilon ' and tan delta do not immediately take the new values, but approach new ones gradually. An attempt is made to explain these results in terms of a space-charge polarisation, recombination and field-enhanced dissociation of impurity ions. The carrier mobility has been estimated from the nonlinear current response under the application of sinusoidal AC voltage.