Capacitance and Loss Variations with Frequency And Temperature in Composite Insulation

Variations in electrical properties of composite insulation with changes in temperature and frequency are important because they lead to concepts of physical causes of such variations and, therefore, indicate how to obtain improved electrical properties in commercial materials. Typical experimental data are presented showing the capacitance and loss characteristics of synthetic resin laminated materials and of imperfect composite dielectrics made from combinations of fused quartz or glass and semi-conducting liquids. An example is given showing agreement between calculated and observed characteristics of such a glass-liquid combination. Theoretical analyses are given, showing that the general form of the capacitance and loss characteristics could be caused by any one of several physical mechanisms. As a result of these studies it seems probable that in synthetic resin laminated products semi-conducting materials in small insulated pockets or fibers can account for observed characteristics and can be represented mathematically by the Maxwell-Wagner theory. It is also shown that capacitance and loss measurements at one frequency and temperature cannot generally be used to predict corresponding values under different conditions.