Abstract:The preparation of insulated core plays a crucial role in the production of 27.5 kV cable for electrification railway. The influence of high insulation eccentricity on thermal extensibility of insulation was investigated. The results showed that the high insulation eccentricity caused the thermal extensibility of the same insulation core to be inconsistent at difference positions. The insulated core of 27.5 kV cable (1 mm×400 mm) was continuously produced via 35 kV catenary medium voltage production line equipped with EHT and wire twisting machine. Combined with the monitoring results of the on-line deviation measuring instrument and that of the sampling (offline slicing sample) with the digital image-type precision measuring instrument, the insulation eccentricity was less than 6%, which is better than that of GB/T 28427—2012 standard. During the cross-linking process, the gel content and thermal extensibility of insulation increased at the first and then decreased with the increasing of the overall temperature of cross-linking pipeline. This phenomenon might be attributed to the over-crosslinking of insulated core when the temperature of pipeline was up to 40 ℃. Therefore, the optimal temperature parameters of each temperature zone of the cross-linking pipeline was chosen as 480-420-380-360-340-320 ℃. The five samples were randomly selected to verify the uniformity of various properties of insulated core after the cross-linking process. The analysis results showed that the gel content, thermal extensibility and tensile properties of insulation are relatively uniform, indicating that the cross-linking degree of whole insulated wire is similar.