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To investigate the partial defects positioning method of low voltage cable, frequency domain reflectometry (FDR) was used to test the low voltage cable with defects, and the positioning results were analyzed in this paper. Three partial defects of D1, D2, and D3 were made successively in phases A, B, and C of 14.1 m long low voltage cable. The D1 defect was a 20 mm × 2 mm of rectangular insulation (expose cable core) in phase A made at 8.7 m away from the head-end of cable and was paralleled resistors with different resistance to simulate high and low resistance faults. The D2 defect was a longitudinal knife mark defect with 5 mm of length in phase B made at 4.3 m away from the front end of cable, while D3 defect was a V-shaped knife mark defect in phase C made at 11 m away from the head-end of cable. The A phase samples without defects and A, B, and C three phase samples with defects were tested by FDR instrument. Then, the D3 defect was immersed in saturated salt water and the three phases end of cable was applied 1 kV voltage for accelerated ageing. The ageing time was four weeks. After ageing, the three phases A, B, and C were detected by FDR. The waveform characteristics in frequency domain and time domain of different defects were analyzed according to FDR detection results. The results show that the peak amplitude in frequency domain of the sample without defect decreases, but the peak amplitude at the defect of the sample with defects increases and is larger than the waveform amplitude on both sides, and the peak amplitude increases more significantly when there is a low resistance fault. In addition, the time domain waveform of high resistance fault shows a positive wave, but the peak is not significant. The low resistance fault presents a significant negative wave. FDR waveforms in frequency domain and time domain can be used to locate low voltage cable faults effectively, and have higher sensitivity to locate low resistance fault.
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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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