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Malfunctions in the insulation system of high-voltage cable terminations can directly trigger breakdown faults, which severely undermines the normal operation of high-voltage transmission lines. In this paper, after analyzing a 110 kV cable terminal breakdown accident, it is found that the lead seal at the terminal tail pipe had partially fallen off, meaning that the metal sheath of the cable had failed to ground at this location. Using the PSCAD/EMTDC electromagnetic transient simulation software for calculation, it was revealed that when only the lead seal detachment (metal sheath grounding resistance) was considered, the voltage rise inside the terminal was relatively weak, and it would be difficult to cause insulation failure of the terminal in a short period of time. Based on this, this paper considered the situation where the cable was invaded by lightning overvoltage. In this case, due to the complex internal structure of the cable terminal, it was more prone to electric field distortion, which eventually led to terminal insulation deterioration, failure or even breakdown. For this scenario, the finite element method was employed to simulate and calculate the electric field distortion inside the terminal when lightning over-voltage intrusion occurred under different degrees of lead seal detachment. The simulation results show that the degree of lead seal detachment has a significant influence on the induced voltage of sheath. With the increase of grounding resistance, the induced voltage on the cable metal sheath first rises and then tends to stabilize, and the equivalent resistance reaches approximately 105 Ω at the stabilization stage. Under the same conditions, the internal electric field distortion of the the cross-interconnected grounding mode is more serious than that of the head-end grounding mode. Additionally, after fitting the results with the least squares method, it is found that the field strength distortion of the terminal main insulation is linearly affected by the cable core voltage and the sheath induced voltage, while the field strength distortion of the sheath surface is only linearly related to the sheath induced voltage.
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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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