Dielectric Loss of EPDM Insulation Subjected to Thermal Stress and Pressure

The insulation performance of ethylene propylene diene monomers (EPDMs) subjected to multi-stresses in the field is always obscure. To understand the effects of temperature and pressure on the performance of the EPDMs used as insulators for power cables, in this work, focuses were on the dielectric losses of EPDMs under the temperature range of 30–
$120^{\circ }\text{C}$
and pressure range of 2–8 bar. The polarization and depolarization currents and the dielectric loss factor of EPDMs under the above conditions have been first measured. The relationship between the depolarization current and dielectric loss factor has been studied based on the correlation of the depolarization charge and the dielectric loss factor at low-frequency. The experimental results showed that the conduction currents and the dielectric loss factor increase with the increase in temperature, but the effect of pressure on the dielectric properties of EPDM is more complicated. There is a strong correlation between the depolarization charge and low-frequency dielectric loss factor, both of which can reflect the change law of the EPDMs’ performance. Moreover, the asymmetry coefficient of the dielectric loss factor at low-frequency can be a supplement with regard to describing the deterioration degree of EPDM insulation. The evaluation chart of the insulation performance of the EPDMs has been advanced according to the asymmetry coefficient and the total dielectric loss calculated by the polarization and depolarization currents.