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Source: insulation materials, No. 3, 2020
Authors: he Hongming 1, Qiu Manshi 2, Nie Zhangxiang 1, Li Yonglan 2, Yu Xin 1, Zhang Yuanyuan 2, Jin Haiyun 2
Setting: 1. Electric Power Research Institute of Guangdong Power Grid Co., Ltd.; 2. State Key Laboratory of electric equipment electrical insulation, Xi'an Jiaotong University
Background XLPE is widely used in power cable insulation because of its good electrical and physical and chemical properties. However, in the actual operation, the physical and chemical properties and electrical properties of cable will deteriorate under the long-term combined effect of humidity, heat, electrical and mechanical stress, which will affect the service life of cable. With the rapid development of urban power grid construction, the demand for XLPE cable has increased greatly. Scholars at home and abroad have carried out a lot of research on the influence of thermal aging on the insulation performance of XLPE cable. However, the comparative study on the thermal and mechanical properties of XLPE cable insulation under high temperature has not been reported in the aerobic and anaerobic environment.
In this study, the high temperature aging process of 110 kV XLPE cable insulation materials in air and silicone oil medium was compared, and the effect of oxygen on the aging process and performance was studied, and the aging mechanism was revealed. Results and analysis 1. Melting heat effect
Figure 1 shows the DSC melting curve of the XLPE insulation sample aged in air and silicone oil. It can be seen that with the increase of aging time, the melting peak of the XLPE insulation sample aged in both media gradually moves to the low temperature direction, and the peak shape changes from steep to gentle. Compared with the silicon oil group, the melting temperature of the air group moved to a lower temperature, indicating that more molecular chains were broken and smaller grains were formed during the thermal oxygen aging process, resulting in a lower melting temperature of XLPE insulation.
▲ (a) air group sample
▲ (b) sample of silicone oil group
Fig. 1 DSC curve of aging XLPE insulation samples in different media
Figure 2 shows the change rule of peak melting temperature of XLPE insulation sample aged in air and silicone oil. It can be seen that compared with the non aged sample, the peak melting temperature of the sample aged for less than 16 h in air group has no significant change at 180 ℃.
Figure 2 peak melting temperature of aged XLPE insulation samples in different media
Figure 3 shows the change rule of the crystallinity of XLPE insulation sample aged in air and silicone oil with aging time. It can be seen that the crystallinity of the two groups of samples decreases with the increase of aging time. The crystallinity of the thermal aging sample in air decreases faster and more rapidly than that of the thermal aging sample in silicone oil.
Figure 3 crystallinity of aged XLPE insulation samples in different media
2. Thermal degradation performance
Fig. 4 shows the thermogravimetric curves of XLPE insulation samples with different aging time in air and silicone oil. It can be seen from Figure 4 that the initial decomposition temperature of the two groups of samples decreases with the increase of aging time, but the TGA curves of the samples with different aging time in silicone oil are relatively concentrated, while the TGA curves of the samples with different aging time in air are more dispersive.
▲ (a) air group sample
▲ (b) sample of silicone oil group
Fig. 4 TGA curves of aged XLPE insulation samples in different media are used to calculate the activation energy of two groups of samples. The results are shown in Fig. 5. It can be seen that the activation energy of thermal decomposition of air group samples increases first and then decreases rapidly with the increase of aging time, while that of silicone oil group samples decreases slowly with the increase of aging time.
Fig. 5 activation energy of aged XLPE insulation samples in different media
3. Mechanical properties
Figure 6 shows the mechanical properties of XLPE insulation samples with different aging time in air and silicone oil. It can be seen from Fig. 6 (a) that with the increase of aging time, the elongation at break of two groups of XLPE insulation samples shows a trend of slow decline first and then rapid decline. It can be seen from Fig. 6 (b) that the tensile strength of two groups of XLPE insulation samples also decreases with the increase of aging time.
▲ (a) elongation at break
▲ (b) tensile strength
Fig. 6 conclusion of mechanical properties of XLPE insulation samples aged in different media (1) in high temperature air and silicon oil media, with the increase of aging time, the melting temperature of XLPE insulation samples decreased, among which the melting peak temperature of heat aging samples in air remained basically unchanged due to the effect of antioxidant, and then the decreasing trend was more intense and the degradation was more thorough.
(2) With the increase of heat aging time, the crystallinity of XLPE insulation sample in air decreases slowly at first because of heat, and then decreases rapidly because of the acceleration of thermal oxygen reaction; however, the crystallinity of XLPE insulation sample in silicone oil keeps a relatively slow decline trend. (3) With the increase of thermal aging time, the activation energy of thermal decomposition of XLPE insulation sample in air increases first, and then decreases rapidly due to the combined action of thermal oxygen; while the activation energy of thermal decomposition of XLPE insulation sample in silicon oil decreases slowly due to the action of heat and a small amount of dissolved oxygen. The United role of. (4) In the process of high temperature degradation, with the increase of aging time, the elongation at break of aging samples in air and silicone oil decreased slowly and then rapidly, and the overall trend of tensile strength was consistent with the crystallinity. This article has been deleted. If you need to read the details, please refer to the 3rd issue of insulation materials in 2020, or click "read the original" at the end of the article to read online.
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