冷热循环对电缆附件界面压力及带材材料特性的影响

Effect of Thermal Cycling on the Interface Pressure of Cable Accessories and Their Strips’ Material Properties

电缆附件是电网输电系统最为薄弱的环节,而附件与电缆主绝缘之间的“抱握力”则是保证附件正常运行的关键因素之一。目前尚缺乏针对电缆附件在安装后界面压力变化情况与成因的相关研究。为此,针对目前电力系统所采用的3种主流10 kV电缆附件,在3种不同温度下,进行冷热循环老化实验,并对附件带材一并进行了老化处理。电缆附件样本内部界面处预制压力传感器,用于测试实验过程中界面压力的变化情况。结果发现:附件界面压力在冷热循环过程中会经历一个先增大后逐步减小的过程,随着温度的升高,最大面压会增大,同时到达最大面压的时间会缩短,这一过程与硅橡胶材料的弛豫特性与“呼吸作用”有关;热处理状态下的附件面压损失要远大于冷却状态。随后,对附件相关带材进行力学性能测试与表面形貌观察,分析发现,带材在循环仅20 d后,表面疏水层与粘连剂就已经基本消失殆尽,至循环结束,材料明显硬化,仅轻微弯折,表面就会出现明显的裂痕,带材的老化与不可用速度明显快于电缆附件本体。面压的损失与带材的快速失效将对附件进水防护等产生较大的隐患。

Cable accessories are the weakest parts in the power transmission system, of which the “holding force” is one of the key factors to ensure the cable lines to run normally. At present, researches on how the interface pressure will change after installation of accessories are rarely available in the literature. Therefore,three mainstream 10 kV cable accessories were selected to conduct thermal cycling aging experiments at three different temperatures. And the same operation was carried out the accessory strips as well. Furthermore, prefabricated pressure sensors were used to test the change of the interface pressure. It is found that the interface pressure of the installed accessory will firstly increase and then gradually decrease during the whole thermal cycles. Besides, as the temperature increases, the maximum surface pressure will increase and the time to reach the maximum surface pressure will be shortened,which can be explained by the relaxation characteristics and the “breathing effect” of silicone rubber(SiR). The test results show that the surface pressure loss is much greater when the applied temperature is relatively higher. Subsequently, the mechanical property test and surface morphology observation reveal that the strips will fail quickly after being thermal cycled for only 20 days.When thermal cycling is over, the strip materials have already hardened with only slightly bent, obvious cracks will appear on the surface, which illustrates that the aging and invalidation speed of the strips is significantly faster than that of the cable accessory. The loss of surface pressure and the rapid failure of the strips will cause greater hidden dangers to the water ingress protection of the accessories.