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Large generators are affected by factors such as thermal stress during operation, resulting in deterioration or even failure of stator bar insulation, which affects the safe and stable operation of the generator. In order to clarify the effectiveness of the polarization and depolarization current (PDC) method for evaluating the main insulation performance of stator bars, at first, PDC method was used to evaluate the main insulation performance of stator bars in the thermal ageing state. According to the PDC test results, the basic characteristic parameters such as the steady-state conductance current, 0.1 Hz polarization/depolarization loss, and asymmetry coefficient were extracted. Then, singular value decomposition (SVD) algorithm was used to analyze the PDC data of the bar sample with the extended Debye model, and the branch number and branch parameters of its analog circuit were obtained. Through analysis, the change regulation of the above characteristic parameters during ageing was clarified. Finally, Fourier transform infrared spectrum (FTIR) analysis was conducted on samples with different thermal ageing durations to further clarify the mechanism of post-insulation curing and degradation from a microscopic perspective. The results show that as the degree of insulation ageing intensified, the steady-state conductivity current and 0.1 Hz polarization/depolarization loss increases, the degree of asymmetry coefficient deviation from 1 intensifies, and the interface polarization time constant τ2 decreases.
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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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