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The physical process of initiation and development of surface flashover in oil-paper insulation of transformer is complicated, and the discharge mechanism remains unclear. In this paper, through experimental measurement and numerical simulation of the needle-plate electrode model for oil gap discharge and the needle-plate electrode model for oil-paper insulation surface flashover, the discharge characteristics and discharge mechanism of oil gap discharge and oil-paper insulation surface flashover under different thickness of paperboard and different surface distance were obtained and analyzed. The results show that under DC voltage, oil-paper insulation surface flashover voltage is lower than the breakdown voltage of oil gap, this is because the paperboard not only changes the distribution of electric field, increases the parallel electric field component at the needle tip, and decreases the initial voltage of the streamer discharge, but also hinders the spread of space charge, enhances the distortion of electric field, and increases the development speed of streamer. In addition, due to the presence of paperboard, the initiation process of streamer in oil-paper insulation surface flashover discharge is completely different from that of oil gap discharge, that the streamer gradually propagates from the tip to the oil-paper interface. Increasing the thickness of paperboard can increase the parallel component of the electric field at the tip, decrease the initial voltage of the discharge, decrease the development speed of the streamer and reduce the surface flashover voltage. The surface flashover voltage of oil-paper insulation increases with the increase of the surface distance, but its nonlinear variation is due to the effect of applied voltage weakens gradually and the effect of space charge distortion electric field is dominant in the process of the streamer developing to the self-supporting discharge stage.
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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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