Influence of temperature on dielectric properties of EPR and partial discharge behavior of spherical cavity in EPR insulation

Ethylene propylene rubber (EPR) with outstanding high temperature performance has been widely used as cable insulation. To understand the influence of temperature on the feature of EPR, a series of study has been conducted including the dielectric measurements, the breakdown voltage and PD behavior of cavities. In the experiments, the dependency of permittivity, conductivity and electric modulus on frequency and temperature has been investigated firstly. Then, the experiments of breakdown voltage have been performed under the applied voltage in the temperature range from 25 °C to 200 °C. Finally, PD behavior caused by artificial spherical cavities in EPR has been examined at the temperature of 25 °C, 100 °C and 150 °C, respectively. It can be concluded by the experiments that the relaxation processes of EPR similar to other polymer materials can be featured by a rapid decrease of the real part of complex permittivity and a slow decrease of dissipation factor with increasing frequency at higher temperature. The dielectric dispersion phenomena can be observed on the spectroscope of the electric modulus which follows the Havriliak/Negami model. The phase resolved PD distribution, such as φ-q-n plots and φ-n plots, caused by cavities can be characterized as the "multi-stem-like" distribution. The repetition rate, the average discharge power and the average discharge current have shown a more strong dependency on the temperature.