Influence of cavities on the dielectric properties of Ethylene Propylene Rubber insulation

Cavities are one of the typical defects leading to the degradation of Ethylene Propylene Rubber (EPR) insulation in extruded power cables. It had been observed by previous experiments that ageing phenomena on the surface of dielectric bounded cavities (DBC) and electrode bounded cavities embedded in EPR insulation was different. The surface of DBC is corroded by partial discharges (PD) which leads to the decrease of surface conductivity. To describe this phenomena, it is essential to analyse the dielectric properties of EPR insulation. So this paper is concerned on the investigation of EPR dielectric behavior which involves permittivity and dissipation factor in frequency domain (0.01 Hz ~ 1 MHz). It has been found by the experiments that the dielectric loss of pure samples are increased with the increase of temperature in low frequency region. The real permittivity of pure EPR have the temperature dependence only in lower frequency region. The real parts of complex permittivity of samples with DBC and EBC is larger than that of EPR without cavities. Moreover, the dielectric loss of samples with DBC is more sensitive to frequency in low frequency region. Thus, the study of dielectric properties is effective for assessment of EPR insulation caused by cavities. The corrosion can be observed on the surface of DBC aging under AC voltage.