GIL三支柱绝缘子机械应力超声检测技术

Ultrasonic Detecting Technology of Mechanical Stress in GIL Three-post Insulators

应力集中会导致三支柱绝缘子出现微气隙或微裂纹,使其机械性能和绝缘性能下降。为此进行550 kV GIL三支柱绝缘子径向、轴向载荷下应力仿真和试验研究,提出标准试样的平行应力声弹性系数测量方法和GIL三支柱绝缘子机械应力超声纵波检测新方法——用标准试样测量材料的垂直应力声弹性系数、平行应力声弹性系数,基于该系数和声弹性方程,通过测量三支柱绝缘子内部的超声声速得到其应力分布。结果表明:环氧复合材料平行应力、垂直应力声弹性系数分别为4.477×10^(-4) MPa^(-1)、8.908×10^(-5) MPa^(-1)。超声穿透法可以检测三支柱绝缘子径向载荷下柱腿环氧的应力,超声反射法可以检测轴向载荷下柱腿嵌件外围环氧的应力,应力检测值与仿真值一致性较好,并分析了误差原因,为GIL三支柱绝缘子机械应力提供了一种无损检测技术。研究还发现,三支柱绝缘子机械断裂属于脆性断裂,断裂发生在柱腿的环氧-嵌件界面,绝缘子径向载荷下的破坏取决于该界面曲率最大处环氧的拉伸强度,轴向载荷下的破坏取决于该界面的剪切强度。

Micro air gaps or micro cracks may be induced by the stress concentration of GIL three-post insulators, which will reduce the mechanical and insulation properties. In this paper, mechanical characteristics of three-post insulators in a 550 kV GIL under radial and axial loads are simulated and tested. New measurement methods of acoustic elastic coefficient under the parallel stress in standard specimens and ultrasonic longitudinal wave detecting mechanical stress in GIL three-post insulators are proposed, respectively. The acoustic elastic coefficients of parallel stress and vertical stress are measured with standard specimens. Based on the coefficients and the equation of acoustic elasticity, the stress of three post insulators is obtained by measuring the ultrasonic velocity. The results show that the acoustic elastic coefficients of epoxy composite material under the parallel stress and vertical stress are 4.477×10^(-4) MPa^(-1) and 8.908×10^(-5) MPa^(-1), respectively. The stress of stressed post in the insulator can be detected by an ultrasonic penetration method under radial loads. The stress of epoxy outside the insert can be detected by an ultrasonic reflection method under axial loads. The testing values are consistent with the simulation values, and the errors are analyzed. The methods can be taken as a non-destructive detection technology for mechanical stress of three-post insulators in GIL. Meanwhile, it is also found that the insulator always fractures at the epoxy-insert interface, which belongs to the brittle fracture. The failure of the insulator under radial loads depends on the tensile strength of the epoxy at the maximum curvature of the epoxy-insert interface, and the failure under axial loads depends on the shear strength of the interface.