The dielectric strength and life of impregnated-paper insulation — III

IMPREGNATED-paper insulation, as used in high-voltage power cables, is subject, during the ordinary processes of manufacture, transportation, installation, and operation, to a wide variety of conditions, nearly all of which militate against the conservation of the original inherent properties of the insulation. Among these conditions are bending and other mechanical stresses, expansion and contraction due to temperature changes, original variations in manufacturing processes of drying and evacuation, and so forth. As a consequence, the electrical characteristics of the insulation of high-voltage cables, as for example power factor, dielectric loss, dielectric strength, and stability, all fall noticeably below those of samples prepared in the laboratory and generally are not subject to all the disturbing conditions mentioned above.