Study on thermo-oxidative aging characteristics of XLPE cable insulation under different oxygen concentration

In order to investigate the effect of oxygen concentration on thermo-oxidative aging characteristics of crosslinked polyethylene (XLPE), 110 kV XLPE cable insulation samples were accelerated aged at 160 degrees C under different pressures of the aging atmosphere of 0.1, 0.06, 0.04 and 0.02 MPa. The microstructure and breakdown strength of XLPE samples were characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and electrical breakdown test at 50 Hz, respectively. The results show that the melting temperature, crystallinity and breakdown strength of XLPE samples decrease slightly or remain unchanged at first and then decrease rapidly with the increase in aging time. The higher the pressure of the aging atmosphere, that is, the higher the oxygen concentration, the earlier the inflection point where the above parameters begin to decline rapidly appears. By testing the oxidation induction time (OIT) of different aging samples, it can be found that the time when this inflection point occurs corresponds to the time required for the antioxidants to be completely consumed in the aging process. Finally, the relationship between the inflection point time and the pressure of the aging atmosphere during the thermo-oxidative aging at 160 degrees C is given in this paper.