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During the operation of high-voltage DC cables, space charge generates in the insulation layer, it leads to electric field distortion and even insulation breakdown. In order to study the effect of space charge in the actual operation of cable, we obtained the temperature field of high-voltage direct current submarine-land composite cable under the conditions of rated current, maximum steady-state current, and short-term overload current, respectively. According to the simulation results, the temperature difference in the space charge test was set as 10℃, 20℃, and 40℃, respectively, and then the temperature field of 400 kV high-voltage DC cable under different condition was simulated. The results show that the temperature difference between the two sides of XLPE insulation layer is 8.1℃ and 18.7℃under rated current and the maximum steady-state current, respectively; while the temperature difference is 61.1℃ under the short-term overload for 1 hour; and that is 41.1℃ under short-term overload for 36 hours. The experimental results show that the temperature gradient enhances the accumulation of heteropolar charge at the low temperature side of positive pole of XLPE, which leads to the distortion of electric field. Through the correction computation of the electric field distortion rate, it is found that the maximum electric field distortion rate has a linear relationship with the average electric field strength. With the increase of temperature gradient, the electric field distortion rate also increases. The maximum electric field distortion rate is 1.68 under the temperature gradient of 40℃ with the applied electric field of 50 kV/mm.
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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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