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With the increases of voltage level and main insulation thickness of high-voltage cable, the thermodynamic operating conditions of cross-linked polyethylene (XLPE) main insulation have become more complex. High-temperature thermal elongation performance is the key to evaluating the thermodynamic properties of XLPE. However, the mechanism research on the differences in thermal elongation performance of different XLPE samples remains insufficient. This paper aimed to comprehensively elucidate the underlying mechanism of thermal elongation performance differences of XLPE high voltage cables under different atmospheres. The thermal elongation performance of three kinds of domestic and international XLPE samples were measured under air, nitrogen, and vacuum atmospheres, and their differences in cross-linking density were analyzed. The cross-linking network structure of XLPE was characterized through gel content and molecular chain structure, and the thermal-oxidative ageing characteristics of XLPE were discussed combined with gel content, carbonyl content, and oxidation induction time. The results show that the high-temperature thermal elongation performance of XLPE is determined by its cross-linking network structure and thermal-oxidative ageing resistance. The XLPE with higher cross-linking density and better thermal-oxidative ageing resistance exhibits lower thermal elongation and permanent elongation. The thermal elongation test under air atmosphere will induce the thermal-oxidative ageing reaction of XLPE, resulting in the reduction of XLPE gel content and the increase of carbonyl content, which will destroy the cross-linked network structure, making the thermal elongation and permanent elongation of XLPE slightly higher. Conversely, the thermal elongation tests under vacuum or nitrogen atmospheres can prevent the damage of thermal-oxidative ageing to cross-linking network, and reflect the true crosslinking degree and thermodynamic properties of XLPE. This work can provide a more effective theoretical basis and testing method for assessing the thermodynamic performance 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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