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To resolve the issue that the traditional frequency domain reflection (FDR) method is easy to misjudge when diagnosing the moisture defects of cable joints, the influence law of thermal excitation on the characteristic impedance of moistened cable joints was firstly analyzed in this paper, and a diagnostic method for moisture in cable joints was proposed based on the frequency domain reflection characteristics under thermal excitation. Then a moistened joint was set up on a 10 kV XLPE cable with a length of 58 m, the temperature of the moistened joint was changed using a heating belt, and the moisture defects were located and diagnosed. The results show that when applying the thermal excitation, the unit capacitance and characteristic impedance of the cable body and normal joint hardly change with the temperature, the unit capacitance of the moistened cable joint decreases with the increase of temperature, and the characteristic impedance increases with the increase of temperature. The simulation results show that the amplitude of the frequency domain reflection spectrum at the moistened joint increases with the increase of temperature, while the amplitude of the frequency domain reflection spectrum at the normal joint is basically unchanged. Based on the above research results, the amplitude changes of the true cable reflection coefficient spectrum at the joint under different temperatures were obtained through thermal excitation, achieving the localization diagnosis of moisture defects.
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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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