Dielectric Behavior of Cellulosic Insulating Paper Subjected to a Combined AC and DC Electric Field

The effect of high dc-fields on the ac-dielectric response was studied in cellulosic insulating papers. Measurements of the complex permittivity were carried out in a frequency range from several Hz to 1 MHz with a custom-made dielectric test setup. Non-impregnated and oil-impregnated papers were investigated with different water contents. The real and imaginary components of the complex permittivity increased considerably at lower frequencies when a high dc-field was applied simultaneously. The increase depended on the water content of the paper and on the amplitude of the applied electric field. It is suggested that ionic motions in hydrated cellulose caused by a high dc-field had an effect on the complex permittivity in a frequency range determined by the time constants of movements of ionic species.