In the extrusion process of XLPE cable materials, when the local extrusion temperature is higher than the decomposition temperature of crosslinking agent, the crosslinking agent will be thermally decomposed in advance, resulting in a low degree of pre-crosslinking in materials. To study the effect of pre-crosslinking on the space charge characteristics of XLPE DC cable materials, the low-degree pre-crosslinking treatment at different temperatures (140℃, 150℃, and 160℃) was carried out before high-temperature crosslinking of XLPE DC cable materials. The aggregated structure was characterized by X-ray diffraction, differential scanning calorimetry, and crosslinking test, and the space charge characteristics at different temperatures were studied. The results show that pre-crosslinking will hinder the normal crosslinking process of XLPE at high temperature, which leads to the decrease of crosslinking degree and crystallinity. Incomplete crosslinking structure makes the pre-crosslinked XLPE samples accumulate a lot of the same polarity of charges injected by electrodes. At the same time, more impurity molecules remaining in the sample will dissociate with the increase of temperature to produce large number of the different polarity of charges, which leads to serious electric field distortion. The decrease of crystallinity also leads to the increase of trap density and depth at the interface between the crystal region and the amorphous region, which limits the charge migration and detrapping process.
| 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 |