III---Accuracy Required in the Measurement of Dielectric Power Factor of Impregnated Paper-Insulated Cables

This paper deals with the effect of errors in the measurement of power factor upon the usefulness of impregnated paper-insulated cables. It points to error in the knowledge of the thermal properties of the cable and the cable duct. The latter error affects the usefulness of a cable to such an extent as to permit a limited error in the power factor without materially reducing the efficiency of the cable. This limited error defines the required power-factor accuracy. The required power-factor accuracy in general is found to vary directly with the frequency and the specific inductive capacity of the insulation, and to increase with the number of cables in a duct bank and the ratio of E²/G, where E is the operating voltage of the cable in kilovolts and G is the geometric factor. For very high-voltage single-conductor cables the power-factor accuracy should be within the order of 0.002.