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Oil-immersed power transformers are the core power transmission and transformation equipment in power systems. The internal oil-paper insulating materials of these transformers undergo deterioration such as moisture absorption and ageing during long-term operation, which seriously threatens the stable operation of the transformers. The AC conductivity behavior of oil-paper insulation composite system can effectively characterize the deterioration degree of the insulation. However, traditional AC conductivity calculation models of oil-paper insulation do not consider the effect of multiple relaxation processes in medium, resulting in low availability of these conventional models. In this paper, the frequency domain dielectric response measurements were performed on aged and damped oil-paper insulation samples at different test temperatures. A theoretical calculation model of AC conductivity variation characteristics in multiple relaxation process of oil-paper insulation system was constructed by means of relaxation and conductivity two shifting. The results show that after ageing, both the conductivity activation energy and relaxation activation energy of the oil-paper insulation decrease, while the effects of moisture on these two activation energy are opposite. The AC conductivities of oil-paper insulations with different ageing degrees at high frequency are basically consistent, and there is a significant transition area in the medium and high frequency ranges, while there is no smooth transition in the AC conductivity curve of the damped sample across the entire frequency range. Meanwhile, using the modified calculation model proposed in this paper can improve the accuracy of low-frequency AC conductivity calculation.
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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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