Effect of DC Superimposed Opposite-polarity Lightning Impulse on Insulation Performance of XLPE Cables

Le résumé fourni par la source

To investigate the effect of DC superimposed with opposite-polarity lightning impulse on the insulation performance of cross-linked polyethylene (XLPE) cable, this paper built a dedicated experimental platform. Based on maintaining a stable DC voltage on XLPE film samples, opposite-polarity lightning impulses with different numbers of applications were applied. The results show that as the number of impulses increases, the DC breakdown strength of XLPE insulation decreases significantly. After 300 consecutive impulses, the DC breakdown strength decreases by 48% compared to that without impulse, and the dispersion increases. Isothermal relaxation current (IRC) tests indicate that as the number of impulses increases, the trap density of the material increases significantly, and the trap energy level deepens continuously. Space charge measurements further show that the dynamic behavior of space charge inside the material becomes more complex after multiple impulses. To reveal the physicochemical mechanism of the effect of impulse number on the dielectric properties of XLPE insulation, multi-scale characterization of the samples was carried out using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and fourier transform infrared spectroscopy (FTIR). The results show that as the number of impulses increases, the initial thermal decomposition temperature and crystallinity of XLPE insulation decrease significantly, while the intensity of characteristic absorption peaks of aging functional groups such as carbonyl groups in the infrared spectrum continues to increase. Comprehensive analysis reveals that lightning impulses cause XLPE molecular chain breakage accompanied by generation of small molecular fragments. Meanwhile, the polarization loss caused by the periodic reversal of the electric field during the impulse process converts into thermal effects, thereby accelerating the thermal-oxidative aging reaction and promoting the generation of more aging products. Pearson correlation analysis further confirms a strong correlation between the evolution of trap characteristics and the degradation of breakdown performance, thus establishing a direct quantitative relationship between microstructural damage and macroscopic performance deterioration, and profoundly revealing the influence mechanism of the impulse accumulation effect on dielectric properties.

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