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In view of the degradation of insulating properties of ethylene propylene diene monomer (EPDM) cables caused by mechanical, electrical, and thermal stresses during operation, the dielectric spectrum of EPDM used for power cable insulation in tensile state was studied. Firstly, a tensile force applying fixture was designed, and a multi-stress dielectric spectrum testing system was built. The dielectric spectrum of EPDM under the joint action of tensile force and thermal stress was measured. The influence of tensile ratio on the dielectric loss factor of EPDM was analyzed emphatically. Then, the characteristic parameters of dielectric spectrum and their variation with tensile ratio were obtained by Cole-Cole model. The change of chemical groups of EPDM was analyzed by Fourier transform infrared spectroscopy (FTIR) from the microscopic view. Finally, the properties change mechanism of EPDM after tensile was summarized combining with carrier apparent mobility. The results show that the tensile ratio has significant influence on the complex dielectric constant and dielectric loss factor of EPDM, especially when the frequency is low, the dielectric loss factor decreases at first and then increases with the increase of tensile ratio. The analysis based on Cole-Cole model shows that the DC conductivity, relaxation strength, and relaxation peak frequency of EPDM decrease at first and then increase with the increase of tensile ratio. Combining with Fourier infrared spectroscopy, it is concluded that the EPDM molecular chain will break when the tensile ratio reaches a certain value, and the carrier mobility extracted from the depolarization current decreases at first and then increases with the increase of tensile ratio.
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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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