Predetermination of the A-C. Characteristics of Dielectrics

From the charge and discharge currents of any type of dielectric under continuous potential it is possible to predict accurately the loss, power factor and capacity at 60 cycles. This is done by an empirical determination of the equation for the relaxation function of the dielectric at a given temperature, followed by the application of von Schweidler's method. The method developed is available at any frequency, provided that the continuous potential charge and discharge currents may be measured over initial time intervals comparable with the alternating period. It is shown that agreement of the relaxation function with the t
^-n
expression is not general, but on the contrary, it is confined to dielectrics showing negligible or no irreversible conduction. The inadequacy of the t
^-n
expression is proved on experimental and analytical reasons. Chief among them is the failure of the t
^-n
expression to predict accurately the variation of dielectric loss with frequency. A convenient and sufficient expression for the relaxation function is shown to be a sum of three exponentials. Further, experiment and analysis prove that the method of three exponentials predicts accurately the a-c. behavior of a dielectric at 60 cycles. The usual forms of irreversible conduction encountered are defined and classified. The case where the initial constant current does not obey Ohm's law has been considered analytically in its contribution to the a-c. behavior. The manner in which the complete a-c. behavior of a dielectric is accurately predicted from suitable d-c.