Insulating paper

It is shown that when certain dielectric liquids are mixed with certain semi-conducting liquids in various proportions the power factor of paper insulation impregnated with these mixtures goes through a minimum. For example, cresol, a semi-conducting liquid may be mixed with tricresyl phosphate, a dielectric. The power factor of Kraft paper insulation impregnated with such a mixture is lowest when the blend comprises about 25% cresol and 75% tricresyl phosphate. Clark has studied a number of other mixtures of semi-conducting and dielectric liquids and finds that minimum dielectric loss coincides with a resistivity of impregnant in the region of 1 × 10⁷ to 2 × 10⁷ ohm -centimeters. The dielectric constant of such mixture is high. Kence capacitors made with impregnants of this sort have a higher ratio of capacity to physical volume than those impregnated with chlorinated diphenyl though power factor is higher and dielectric strength lower. Moreover, it is possible to use a single sheet of tissue with these mixtures and capacity is not dependent upon the spacing of metal electrodes. This latter, it is explained, is due to the impregnant acting as a liquid electrode and, therefore, only the paper thickness is the determining factor. Data are presented to show that the power factor and capacity of this new type of capacitor are stable with respect to temperature change and under applied potential both continuous and intermittent.