With the primary advantages of flexibility and an inherent resistance to failures caused by electrochemical degradation, Ethylene-Propylene Rubber (EPR) cables have been widely used in special fields, e.g. coal mine, oil production and submarine cable. However, the cables insulated with EPR will inevitably contain some defects. Cavities are one of the typical defects resulting in partial discharges (PDs) in extruded power cables. The cavity is of a lower relative dielectric permittivity of εr=1 than insulation materials (e.g. s, of cross-linked polyethylene (XLPE) included the spherical cavity is 2.3). As shown in Figure 1, the strength enhancement of the ellipsoidal cavity with same dimensions is directly proportional to relative dielectric permittivity of insulation materials around cavities.
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