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Damage Mechanisms in Medium-Voltage Insulating Polymers under Hemispherical-Plane Electrodes

Controlling the lifetime of insulating materials is required to insure reliability of insulation systems for Medium Voltage (MV) and High Voltage (HV) cables. The aging behavior of Low Density (LDPE) and Cross-Linked Polyethylene (XLPE) under MV-AC thermo-electric stress is studied in the sphereplane geometry in air to identify degradation mechanisms associated to Corona Discharges (CDs) and their impact on insulation lifetime. Times to breakdown values are measured under different applied electric fields. Additionally, XLPE samples are aged to different ageing steps. Then, the samples are analyzed by scanning electron microscopy and infrared spectroscopy to monitor progressive damage during ageing.