Ionization Studies in Paper-Insulated Cables---III

This is the third report to be presented before the Institute of the research investigation of ionization phenomena in paper-insulated, high-voltage cables, which is being conducted at the Harvard Engineering School under the auspices of the Impregnated Paper-Insulated Cable Research Committee. This paper is a report of progress and will be followed by further reports as the work continues. The total power dissipated in impregnated-paper insulation may he separated by the graphical method into the component dissipated in the solid dielectric and that dissipated in the ionized gas films, and also may be separated analytically into these two components by selecting three suitable points on the power curve. This separation gives the three characteristic cable constants. When the power curve of a cable is analyzed into its two components, the ionization-power curve itself should be a straight line. Frequently, however, the ionization-power curve is concaved upwards. This is probably due to the non-linear characteristic of power loss caused by longitudinal and tangential stresses. Hence, it may be assumed when the ionization-power curve is concaved upwards, that longitudinal and tangential stresses exist within the cable. This theory is substantiated by investigations with cable models. The value of the maximum power factor and of the voltage at which it occurs are shown to be very simple functions of the three characteristic cable constants. With a considerable number of cables, the calculated and the experimental values of these quantities are in close agreement.