The main insulation of cross-linked polyethylene (XLPE) HVDC cable was sliced at radial inner, middle, and outer layers to as samples, and their equivalent thermal history was modeled by differential scanning calorimetry (DSC). The changes of chemical and electrical properties of each layer in cable insulation after type test were analyzed by infrared spectroscopy (FTIR), space charge, and DC electrical strength test. The results show that after type test, the equivalent heat treatment temperatures of each layer in cable main insulation are about 70℃, there is a small difference between the equivalent heat treatment time of the middle layer and the outer layer, while the equivalent heat treatment time of the inner layer is about 581 times bigger than that of the middle layer. There are little changes in DC electric strength and chemical properties of each layer in cable main insulation. Due to the equivalent heat treatment time of each layer is different, the impurities, polar small molecules, and other substances in inner insulation layer continue to diffuse from the inner layer to the middle layer, which results in the significant accumulation of heteropolar space charges.
| 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 |