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Both power frequency and 0.1 Hz cosine square wave voltage can be used for withstand voltage assessment of cable, but the equivalence of assessments under two voltages is not clear. For this reason, on the basis of needle plate electrode model, breakdown tests under power frequency and 0.1 Hz cosine square wave voltage were carried out on the samples with different insulation residual thickness defects. The Weibull distribution of breakdown time under different voltages was statistically analyzed, the morphological characteristics of breakdown channel were observed and compared, and the reasons for the difference in the strength of assessment under power frequency and 0.1 Hz cosine square wave voltage withstand voltage were analyzed. The results show that under the condition of needle plate electrode model, the breakdown voltage and breakdown time of the defects under 0.1 Hz cosine square wave voltage are both greater than that under power frequency voltage, which indicates that the strength of cable withstand voltage assessment under 0.1 Hz cosine square wave voltage is significantly lower than that under power frequency voltage. Before the sample is broken down under 0.1 Hz cosine square wave voltage, there is no obvious traces of burning and carbonization, and the cumulative effect is not significant. The reduction of composite electric field intensity and insignificant cumulative effect caused by the charge injection of cosine square wave DC stage may be the reason that the 0.1 Hz cosine square wave voltage on the cable withstand voltage assessment is significantly lower than the power frequency voltage.
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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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