A ±400 kV HVDC model cable was conducted DC withstand voltage test and impulse withstand voltage test, and the DC breakdown voltage and impulse breakdown voltage of the model cable under the highest operating temperature were obtained. The electric field distribution under DC breakdown voltage and impulse breakdown voltage were calculated. On the basis of average field intensity method and maximum field intensity method, the insulation thickness of ±400 kV HVDC cable was designed, and the electric field distribution of insulation layer was calculated under DC voltage and impulse voltage. At last, the insulation thickness of ±400 kV DC cable was obtained by comparing the electric field distribution of ±400 kV HVDC cable and model cable. The results show that when the insulation thickness of HVDC cables is designed by the average field strength method, the insulation thickness depends on the impulse voltage. When the insulation thickness is designed by the maximum field strength method, the insulation thickness depends on the DC voltage. By comparing the electric field distribution of ±400 kV DC cable and the electric field strength of the model cable when breakdown, it is obtained that the insulation thickness of 400 kV DC cable is 26 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 |