A Measurement Method of Ultrasonic Critical Refraction Longitudinal Wave for Thermal Stress in GIS Basin-Type Insulators
Yanpeng Hao, Yao Zheng, Weiming He, Xuezhi Liang, Zhimin Zhang, Lin Liu, Lin Yang, Guoli Wang, Chao Gao, Fusheng Zhou
Abstract
Thermal stress of gas-insulated metal-enclosed switchgear (GIS) basin-type insulators weaken its mechanical properties, which will threaten the safe and stable operation of GIS. In this article, the simulation and experiment of thermal stress in a 252-kV GIS basin-type insulator were carried out. An acoustic-distance difference method based on the ultrasonic critical refraction longitudinal wave (ultrasonic <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L_{\mathrm {CR}}$ </tex-math></inline-formula> ) and a measuring method for propagation depth of ultrasonic <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L_{\mathrm {CR}}$ </tex-math></inline-formula> were proposed respectively: the variation of propagation depth in epoxy composites was measured by ultrasonic probes of different frequencies, and a mapping function between the propagation depth and detection frequency was established. The 2-MHz variable-angle ultrasonic probes were used to test the circumferential thermal stress below the surface of the 252-kV basin-type insulator, and the thermal stress simulation of the insulator was performed. The circumferential thermal stress at different positions of the insulator was obtained and then a contour plot of the stress was established by the cubic spline interpolation. The results showed that the propagation depth of ultrasonic <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L_{\mathrm {CR}}$ </tex-math></inline-formula> in the subsurface of epoxy composites decreased exponentially with the frequency, the mapping relationship of depth-frequency had a good goodness of fit, and the coefficient of determination was as high as 0.988. The circumferential thermal stress at 9 mm below the surface of the insulator was tensile stress, which decreased first and then increased along the radial direction, showing as a V-shaped distribution. The experimental values were in good agreement with the simulation values, which verified the effectiveness of the proposed methods.