覆冰对输电线路的影响主要体现在输电导线和线路绝缘子两个方面。直流融冰技术已经能够有效地解决输电导线的覆冰问题，但目前对绝缘子覆冰及其闪络机制仍然缺乏充分的认识，尚未有抗冰结构设计的理论依据。为此，本文针对绝缘子的覆冰问题，围绕冰棱生长、盐分分布、融冰闪络这一过程开展系统研究。首先，本文通过对短串复合绝缘子的带电覆冰试验，详细地分析了施加电场、环境温度、覆冰水量、覆冰水电导率及染污程度对冰棱生长过程的影响。基于冰棱生长的热力学过程，分析推导出带电覆冰时的冰棱生长模型，揭示了电场与冰棱生长的相互作用，得出了影响稳态冰棱长度和覆冰时间的特征参数。其次，本文对覆冰过程中冰层内的盐分分布规律进行了深入探讨。试验观察过冷却水中盐分的迁移过程，发现迁移方向与冻结方向一致，且盐分迁移仅发生在过冷却水相变前。分析了覆冰水电导率、覆冰速率、染污程度、桥接状态对盐分迁移过程的影响，建立了盐分迁移的物理模型，推导出沿冻结方向冰层中盐分分布的数学表达式。110kV绝缘子串试验验证了上述结论,同时发现，冰层中的盐分分布会改变闪络路径，对融冰闪络过程造成影响。再次，本文研究了未桥接冰棱、桥接冰柱及冰棱-冰柱组合下的闪络特性。试验发现，未桥接冰棱存在沿面电弧和内部放电两种类型。桥接冰柱模型发生闪络需要提供额外的融冰能量，具有较高闪络电压。桥接冰柱易融断，其闪络概率较未桥接冰棱低。冰棱冰柱共存时，在相同间隙占空比条件下，冰棱-冰棱模型更易在低电压下发生闪络。最后，根据带电覆冰条件下的冰棱生长模型，提出了覆冰地区复合绝缘子抗冰结构设计原则，研制了110kV/220kV/500kV三个电压等级共11种覆冰地区用复合绝缘子试品，完成了人工覆冰试验。试验表明，冰棱桥接程度可作为判断覆冰闪络电压高低的依据，试验结果验证了抗冰设计的可靠性。
Nowadays icing problems on transmission lines can be effectively resolved by means of DC-current technology, but few effective methods were applied to the icing process on insulators. This thesis is concentrated on the icing insulators under energized condition, including its icicle growth, salt distribution, melting and flashover. First, experiments on short composite insulators were carried out to reveal the effect of electrical field, temperature, rainfall, applied water conductivity and pollution level. According to the thermodymanics analysis, icicle growth under energized condition had been modeled to reflect the interaction between electrical field and icicle length, which avail to obtain the characteristic parameters affecting icicle length and icing time in steady state. Second, analysis of salt distribution were in depth exploration. Salt migration in cooling water had been observed before phase transition, with the same direction of frozen process. The effects of applied water conductivity, freezing velocity, pollution level and icicle bridged degree were investigated in experiments. Fick’s diffusion law was applied to deduce the change of salt content in the liquid water. This phenomena was verified in 110kV icing insulator experiments, and it was discovered that salt migration could change the flashover path and lead to the variation of flashover voltage.Moreover, typical icing morphology, including bridged and non-bridged icicles, affected the electrical strength under melting conditions. Two different discharge patterns were observed on non-bridged icicles, surface discharge and interior partial discharge. However, fully bridged icicles required extra energy for ice melting, leading to higher flashover voltage and lower probability compared to partially bridged icicles. When the two kind of ice morphology coexisted, a single air gap with bridged icicle had higher flashover voltage than a pair of air gaps. Finally, according to the icicle growth model, the principle of anti-icing structure was proposed and composite insulators of 110kV/220kV/ 500kV were designed and tested in the artificial climate chamber. Experiments show that bridged degree of icicle was in good accordance with the ice flashover voltage, thus could be considered as characteristic parameter to evaluate the electrical performance of icing insulators. Experimental results verified the reliability of anti-icing insulator structure.
