Seismic Response of High-Voltage Transformer-Bushing Systems Incorporating Flexural Stiffeners II: Experimental Study

Abstract

A numerical study conducted on four transformer-bushing models presented in a first companion paper indicated that high-voltage bushings mounted on the cover plates of transformers are more vulnerable to seismic loading than bushings mounted on a rigid base. This would explain why the good performance of bushings mounted on a rigid base observed during shake table testing does not correlate well with their performance in the field. In this second companion paper, the addition of flexural stiffeners on the transformer cover plates as a means to stiffen the base of bushings and mitigate their seismic vulnerability is investigated experimentally. Shake table testing was conducted on a 230 kV porcelain bushing mounted on a support structure incorporating a flexible cover plate and two stiffener configurations. Test results confirmed that stiffening the cover plates is beneficial to the seismic response of high-voltage bushings. Test results are compared to the predictions of finite element analyses.

Sloshing characteristics of annular tuned liquid damper (ATLD) for applications in composite bushings

“…According to the expression of Equation 9, the natural frequency f nm of liquid sloshing in annular cylindrical tank is not only related to the geometries of the tank but also relevant to the eigenvalue ξ nm that can be obtained by solving the transcendental equations of (7) and (8). Here, the transcendental equations involving the Bessel functions are rather complex and can only be solved by the trial method.…”

“…In the last 20 years, many studies had been done to qualify the seismic behavior of bushings and to raise their reliability. The additional flexural stiffeners on the cover plate were beneficial to the seismic response of the bushing, because it increased the fundamental frequency of the bushing close to that of rigid base condition . Considering the additional stiffeners, the maximum reduction in bending moment at the base of bushing was achieved in a range of 53% to 86% compared with the flexible cover plate .…”

“…The additional flexural stiffeners on the cover plate were beneficial to the seismic response of the bushing, because it increased the fundamental frequency of the bushing close to that of rigid base condition. [8,9] Considering the additional stiffeners, the maximum reduction in bending moment at the base of bushing was achieved in a range of 53% to 86% compared with the flexible cover plate. [10] In addition, there are also many other methods used to mitigate the seismic responses of the bushing.…”

Consistent floor response spectra for performance‐based seismic design of nonstructural elements

“…The methodology provides expressions that are valid in a range of nonstructural periods up to the fundamental period of the supporting structure followed by constant spectral displacements for longer nonstructural periods. This approach would lead to inaccuracy when designing or assessing NSEs with periods longer than the period of the supporting structure, such as pendant lighting fixtures, steel storage‐racks, vibration isolated mechanical equipment, or important artworks that could be seismically base isolated . The recent “recommendations for improved seismic performance of nonstructural components” developed by the National Institute of Standards and Technology (NIST) provides some statistical data on the ratios between the fundamental periods of NSEs and of supporting structures.…”

Optimal design of multiple annular tuned liquid dampers for seismic reduction of 1,100-kV composite bushing

“…Ersoy and Saadeghvaziri investigated the influences of the flexibility of the transformer's top plate on the dynamic responses of the bushing in SAP2000. Koliou provided the fragility curves of bushings with different mounted conditions and concluded that the additional stiffeners on the top plate of the transformer would be one of the most efficient retrofit approaches for reducing the bending moment at the base of the bushing Moreover, many/more techniques such as the additional stiffener, the increased preload, and the stiffer gaskets were also adopted to enhance the mounted conditions of the bushings, which would reduce the input motions at the base of the bushing. On the other hand, the base‐isolated technologies, such as the segmented high damping rubber bearings, the wire rope isolators (WRIs) and the friction pendulum systems (FPS) were also used for seismic protection of the bushings.…”