Taking the DC submarine cable in ±525 kV DC transmission project as the research object, we conducted DC voltage withstand test, impact voltage withstand test, and gradient voltage withstand test. The breakdown strength, ageing life index, Bahder's coefficient and other key parameters of the insulation material were analyzed. The insulation thickness of the ±525 kV DC cable under different voltage withstand condition was designed and calculated. The insulation design thickness was calibrated on the basis of the electric field distribution and temperature distribution of DC cable. The results show that the distortion degree of electric field distribution in DC cables is mainly determined by the temperature difference of insulation layer, and the insulation temperature difference is mainly determined by the magnitude of current passing through the cable conductor. Taking into account the research results and the long-term safety and reliability of cable, it is recommended that the insulation thickness of ±525 kV DC cables is designed to be 28 mm.
| 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 |