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Local abnormal heating often occurs in the heat-shrinkable terminals of medium-voltage cables, leading to localized overheating and accelerated ageing of cable insulation, which even causes premature insulation failure. To elucidate the causes of abnormal heating in medium-voltage cable heat-shrinkable terminals, the electric-thermal field of cable heat-shrinkable terminals under various typical fault conditions was simulated by electromagnetic-thermal coupling. The results show that during the long-term operation of the cable, the ageing of the stress control tube leads to localized temperature rise in the insulation. The more severe the ageing, the higher the temperature rise. Furthermore, when the outer surface of the terminal becomes contaminated due to dust accumulation and moisture, a significant hot spot forms near the break of the outer semiconductive layer; however, the hot spot diminishes when the contamination layer is far from the break. Further analysis on the thermal field distribution of the terminal with moisture on the stress control tube reveals that hotspots only appear when the inside of tube is moist. A thermal circuit model considering internal defect hotspots was built, and temperature inversion was implemented to monitor the highest temperature point at the internal insulation interface of heat-shrinkable terminal. It is verified that the method is effective.
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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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