An Investigation of Dielectic Losses with the Cathode Ray Tube

This paper discusses the theory of the cathode ray tube wattmeter and shows how it can be used to determine directly the power factors of insulations. The current and voltage are measured independently so that the dielectric losses in insulation can be calculated. Such measurements can be made up to the breakdown voltage of the material being tested. The development of the cathode ray tube and its auxiliary apparatus is discussed. Measurements of dielectric losses, power factors, and currents, for varnished cloths and oil-treated pressboard, are given. The measurements have been made at 60 cycles at different voltages, temperatures, and moisture contents in the case of pressboard. Curves are given showing the losses, power factors and currents plotted against voltage, temperature, and per cent absorbed moisture. Empirical equations are derived for all the curves. It is shown that watt losses may vary from the 1.32 to the 2.52 power of the voltage. The losses and currents can be expressed by an equation of the form K1 + K2 Yn, where Y may be temperature in deg. cent. or per cent absorbed moisture. The same form of equation holds for the power factors up to about 85 per cent. The equations given show that the exponent n may vary from about four to seven, depending on the conditions of the tests and on the nature of the insulations.