The Measurement of Energy Losses in Condensers Traverse, by High-Frequency Electric Oscillations

Abstract

In this Paper an arrangement of apparatus is described for the purpose of measuring the internal energy losses in condensers traversed by high frequency (H.F.) currents. It is shown that these energy losses in condensers may be considered as if they were due to a resistance loss in a hypothetical resistance in series with the condenser, the condenser itself being supposed to have a perfect non-dissipative dielectric of the same dielectric constant. This hypothetical resistance is not constant, but is a function of the condenser current. The experiments were conducted by the use of a special form of impact dischargers comprising two flat plates immersed in oil, one stationary and the other revolving at a high speed. This discharger was placed in series with a primary circuit and condenser, and H.F. oscillations were set up in the primary having any desired frequency. A secondary circuit loosely coupled consisted of a wire whose H.F. resistance could be determined, the condenser to be examined and a hot-wire ammeter and variable resistances. The measurements consisted in observing the reading of the ammeter, and then changing the current created in the secondary circuit by a small amount by adding a known resistance which altered the decrement of the circuit, but not its inductance. From these readings an equation is obtained for the hypothetical condenser resistance. It is shown that the product of the square of the secondary current A2 and the total resistance R of the secondary circuit is constant, and hence that the unknown condenser resistance ρ can be found from observations of the change in A2 when an additional resistance r1 is interpolated in the condenser circuit. The energy loss in the condenser is then A2ρ watts. Condensers with various dielectrics, air, oil, glass and ebonite, were examined, and the dielectric energy losses D are stated in micro watts per cubic centimetre of dielectric for given values of the electric force E. It is shown thus D can be expressed as a function of E in the form D=XEY, where X is a constant depending on the current density, and Y is a constant depending on the nature of the dielectric. For oil and air these power losses are relatively small, but for glass and ebonite large. The necessity for measuring these losses in the case of radiotelegraphic condensers is emphasised.