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Effect of swelling effect of silicone rubber (SiR) caused by silicone grease coated on the interface between high voltage cable accessories and cable body on the electrical tree characteristics of SiR under monopolar impulse voltage (250/2 500 μs) was studied. The isothermal surface potential decay (ISPD) and equilibrium solvent swelling were carried out to characterize the influence of swelling effect on the trap characteristics and crosslinking structures of SiR. The results show that with the increase of swelling time, both the initiation probability and fractal dimension of electrical tree in SiR increase. After 340 h of swelling, the tree initiation voltage of 50% probability under positive and negative impulse voltage decrease from about 37 kV and about -41 kV to 32 kV and about -39 kV, respectively. In addition, the polarity effect can be observed in the electrical tree process of SiR under impulse voltage. The initiation and growth of electrical tree is easier under positive impulse voltage than negative impulse voltage. With the increase of swelling time, the shallow trap density increases, and the deep trap and physical crosslinking density decrease. The destruction of physical crosslinking structure leads to the expansion of free volume, which intensifies the collision ionization processes. Meanwhile, the decrease of deep trap density enhances the charge transport processes. Multiple physical processes intensify the fracture of molecular chains, which furtherly weakens the resistance to electrical tree of SiR. The polarity effect of electrical tree in SiR under impulse voltage is mainly caused by the different distribution of hole-type and electron-type traps.
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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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