Research On The Uneven Aging Of Composite Insulators In Service

With wider application of composite insulators in power system and longer service term, composite insulators are increasingly exposed to the problem of aging of the material. As the electric strength and environmental influences on the sheds along the insulator string or different region of the single shed are different, the aging state is definitely different. In this thesis, the composite insulators in long term service were studied and the sample selection scheme was developed considering different factors causing the uneven aging. The investigation of uneven aging characteristics of composite insulators had been carried out by hydrophobicity test and Thermally Stimulated Current (TSC) test.The results of hydrophobicity test showed that: the hydrophobicity distribution of insulator string was uneven; the hydrophobicity of the sheds of both ends was poor, while it was good in the middle. There was no significant difference between hydrophobicity distribution of inside and outside insulator. Hydrophobicity distribution of upper surface of the insulators on different orientations had no difference, while it was different of that of lower surface. It meant that there was one orientation which had the poorest hydrophobicity.The TSC test results showed that:the distribution of the trap parameters was uneven. Usually the trap parameters of the sheds of both ends were higher, while they were lower in the middle. The trap parameters of upper surface on the same shed were higher than that of lower surface. Also, the trap parameters of the inside region of the sheds were higher than that of the outside region. Trap parameters distribution of the insulators on different orientations was different, and there was obviously one orientation which had the highest value of the parameters.The linear relationship between the trap parameters of the sheds (lower surface) and the electric field along the insulator string, also the correspondence between the trap parameters of the sheds and the electric field along the radial direction of the same shed, both showed that the surface discharge caused by the electric field of the sheds was the reason of the uneven aging along the string and the radial direction of the sheds. It was the interact result of the UV radiation and the electric field that caused the distribution of the aging characteristics of the upper surface along the insulator string. TSC test results can clearly reflect the aging state of composite insulator sheds, which required little about the surface characters. In summary, TSC test was more effective of assessing the aging state of the composite insulators, and the trap parameters could be the evaluation criteria of aging of the shed material of the composite insulators.