Dielectric properties of electrical insulating materials at very low frequencies

Solid electrical insulating materials, especially nigh polymeric materials, often show dielectric relaxation phenomena in the range of very low frequencies. In order to study such properties, some very low frequency bridges_1,2 have been developed. However, it is tedious to measure the dielectric properties at frequencies below 0.03 cps by the a.c. bridge method. Therefore, it becomes necessary to make use of the method for deducing a.c. characteristics from the absorption current measurement. In this paper, the first, the Hamon´s approximate method is re-examined with the view of determining the magnitude of dielectric dispersion and the frequency of loss maximum, and it is shown that the method is applicable to the present purpose without any restrictive conditions given by Hamon. The second, the linearity of dielectric properties in the range of very low frequencies is examined about some liquid and solid insulating materials and the origins of non-linearity are briefly discussed. Finally, several interesting characteristics of polymers are illustrated in order to prove the utilities of very low frequency measurements.