Abridgment of ionization studies in paper insulated cables — II

The power dissipated as ionization loss in impregnated-paper-insulated cables is much more harmful than the power dissipated in the solid dielectric. The paper presents methods of separating this ionization loss from the total dielectric loss. This separation is based on the assumption that the power loss in the solid dielectric varies as the square of the voltage, even above ionization. To verify this assumption, samples of wood-pulp paper, impregnated with three different cable compounds under such conditions as to remove nearly all traces of occluded gases, were made up. These tests showed that up to 300 volts per mil, and at room temperature, the power factor and capacitance are substantially constant, and that the power loss varies as the square of the voltage. Measurements of the electrical properties of ionized air films showed that above the ionization voltage the power loss is a linear function of the voltage. Power curves of cables can thus be analyzed into two components; one giving the loss in the solid dielectric and one giving the loss in the ionized air films. This analysis is verified with glass cable models. The power-factor curve and the energy current of the cable can each be analyzed into three simple components and extrapolated if desired. The character of the capacitance curve, which varies in different cables, is determined by the positions and thicknesses of the gas films.