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Reasonable prediction of the ageing state of cross-linked polyethylene (XLPE) cables and timely replacement of severely aged cables are very important for the stable operation of power grid. In this paper, XLPE insulated cable samples were subjected to accelerated thermal ageing test at 145℃.The microphysical and chemical properties of these samples were analyzed, and the correlation between dielectric parameters and microstructure of terahertz frequency range was established. The results show that with the increase of aging time, the crystallinity and thermal stability of XLPE decrease, while the carbonyl index increases, indicating that the ageing degree of XLPE is gradually intensified. In the terahertz frequency range, the real part of the dielectric constant is affected by the combination of multiple structural factors such as crystallinity and polar group content, resulting in an unclear relationship with ageing time. However, the change of the imaginary part of dielectric constant is mainly caused by the dipole high elastic polarization of polar groups, showing a trend of gradually increasing with the ageing time. After fitting, it is found that the imaginary part of dielectric constant is positively correlated with the carbonyl index. Therefore, the imaginary part of dielectric constant in the terahertz frequency range can well reflect the ageing degree of XLPE.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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