Abstract
Situations of internal stress in basin insulators inside gas-insulated metal-enclosed switchgear (GIS) can lead to cracks, which can influence the safety and stability of apparatus. However, there is currently no research on internal stress measurements for composites of GIS basin insulators, and only measurements for surface stress. In this paper, an internal stress measurement method for GIS epoxy composite is proposed using an ultrasonic longitudinal through-transmission technique based on the acoustoelastic effect. An internal stress measurement system is developed to investigate the relationship between the uniaxial compressive internal stress and the velocity of the ultrasonic wave vertical to the stress in epoxy composite within a range of 0–70 MPa, and to calculate the acoustoelastic coefficient of epoxy composite. The effects of system delay are eliminated in measuring the propagation time. Some epoxy composite cuboid specimens with similar materials and using a manufacturing process similar to those of 252 kV GIS basin insulators are synthesized, and the uniformity of the internal stress in cuboid specimens is verified by finite element simulation. The results reveal a linear increase of the ultrasonic longitudinal wave velocity with increasing stress. It has been shown that the average acoustoelastic coefficient of GIS epoxy composites, using the longitudinal waves vertical to the stress, is 4.556 × 10−5/MPa. Additionally, the absolute errors of the internal stress measurements are less than 12.397 MPa. This research shows that the ultrasonic method based on the acoustoelastic effect for measuring the internal stress in GIS epoxy composites is feasible.
Highlights
Gas-insulated metal-enclosed switchgear (GIS) has advantages that include high reliability, small ground space requirements, a long maintenance cycle, low environmental impact, flexible construction, good expansibility, etc
Wang et al [19] proposed an equation that determined the relationship between the stress, in the area beneath the surface, and propagation time of critically refracted longitudinal waves in a carbon-fiber-reinforced plastic composite, and concluded that the propagation time was linearly dependent on the stress
The acoustoelastic equation for ultrasonic longitudinal waves in the case of uniaxial stress is defined as Equation (1) in the following [18]
Summary
Gas-insulated metal-enclosed switchgear (GIS) has advantages that include high reliability, small ground space requirements, a long maintenance cycle, low environmental impact, flexible construction, good expansibility, etc. Jia et al [17] found that the velocity of the longitudinal waves changed linearly with the tensile internal stress in certain polymer materials, such as polycarbonate, polystyrene, polyamide, and polybutylene terephthalate They used the longitudinal pulse-echo method to measure the ultrasonic velocity based on the time interval between first and second reflected waves at the back surface. Wang et al [19] proposed an equation that determined the relationship between the stress, in the area beneath the surface, and propagation time of critically refracted longitudinal waves in a carbon-fiber-reinforced plastic composite, and concluded that the propagation time was linearly dependent on the stress They calculated that the acoustoelastic coefficient was consistent with the experimental results. The tangential compressive internal stress, resulting from mechanical compression in the epoxy composite specimens of GIS basin insulators, was measured based on the acoustoelastic effect. The internal stress measurement errors were calculated and analyzed
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