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Trace moisture absorption of insulating oils in high-voltage cable terminations during on-site filling or long-term operation may cause electrical performance deterioration and even insulation breakdown. The differences in molecular structure and polarity characteristics among different types of insulating oils will lead to significant differences in the adsorption behaviors of water molecules and the degradation laws of electrical performances. In this paper, the natural water absorption of silicone oil and polyisobutylene insulating oil under different exposure time was studied. The evolution of moisture content in different temperature and humidity environments was determined by Karl Fischer titration method, and the dielectric loss factor, volume resistivity, and power-frequency breakdown voltage of the insulating oil after water absorption were tested. Through molecular dynamics and quantum chemical calculations combined with Gaussian software, the differences in the moisture absorption mechanisms of the two types insulating oils were revealed from the perspectives of microscopic dipole moment, adsorption energy, and Gibbs free energy. The results show that due to the existence of Si-O bonds and polar groups in molecular chain of silicone oil, the dipole moment is 0.69 Debye. The initial absorption rate and total moisture amount are relatively high, and its moisture absorption process conforms to the exponential growth trend, the saturated moisture content is approximately 52×10-6. The polyisobutylene has a typical non-polar C-H chain structure with a low dipole moment of 0.02 Debye, and the its moisture absorption process shows a linear upward trend. Moisture absorption will lead to a significantly increases in dielectric loss factor, decreases in volume resistivity and electric strength for the two types of insulating oils. Silicone oil fails to meet the national standard requirement for insulation strength after 2 h of exposure, while polyisobutylene maintains good insulation strength within 5 h of exposure.
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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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