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In view of the strong greenhouse effect of SF₆ insulating gas, finding its alternative medium has become an industry consensus. Clean air, as an environmental friendly insulating medium, is considered as a promising candidate for DC GIS equipment. To investigate the insulation characteristics of high-pressure clean air, the breakdown characteristics of air at different pressures (0.6–0.9 MPa) under positive and negative lightning impulse voltages and DC voltage were measured in uniform and slightly non-uniform electric fields with a 10 mm gap. The time-volume theory was introduced, and a breakdown field strength prediction model was established based on this theory. Finally, the model predictions were compared with the experimental results. The results show that in uniform field, the breakdown field strength under negative polarity exhibits greater dispersion. In slightly non-uniform field, among the four cases, the breakdown field strength under negative lightning impulse is the lowest, and the breakdown field strength exhibits a saturation effect with the increase of pressure. The time-volume theory can accurately capture the trend of breakdown field strength changing with pressure. This model considers the electric field enhancement on the electrode surface caused by micro-protrusions, and the predicted results are in good agreement with the experimental results.
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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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