Dielectric properties of aged polyester films

Electrical properties of polyester films aged under cold and hot environment conditions between -40°C and +120°C have been examined. The examined dielectric parameter are dielectric constant and dissipation factor in the frequency range of 50 Hz to 1 MHz and ac electric breakdown strength at 50 Hz. Experimental results have been shown that the AC breakdown strength is inversely proportional to the film thickness and temperature; the frequency has no significant effect on the relative permittivity of polyester under thermal stress, especially at higher temperatures; and dissipation factor of polyester shows nonlinear frequency dependence in high temperatures