03-27-2013, 11:30 AM
(This post was last modified: 03-27-2013, 12:26 PM by pezhmankhan.)
Seismic Protection of Electrical Transformer Bushing Systems by Stiffening Techniques
Author: M. Koliou, A. Filiatrault, A. M. Reinhorn and N. Oliveto | Size: 22.3 MB | Format: PDF | Quality: Unspecified | Publisher: MCEER | Year: 2012 | pages: 234 | ISBN: 1520-295X
In the past few decades, electrical substation equipment has shown vulnerable behavior under
strong earthquakes, resulting in severe damage to electric power networks. High voltage
bushings, which are designed to isolate and transmit electricity from a transformer to the high
voltage lines, are the most critical as well as the most vulnerable components of the electrical
substations. Rehabilitation of existing bushing structures and proper design of new ones could
considerably reduce potential damage to them. Several experimental and numerical studies
conducted to investigate the seismic performance of transformer bushing structures have shown
that improved seismic performance may be achieved for bushings mounted on a rigid base
compared to those mounted on actual transformer tanks (“as installed” conditions), which appear
to be very flexible.
This reports investigates the seismic response of bushing structures both “as installed” on a
flexible base and on a rigid base as well as attempts to identify feasible approaches of stiffening
the base of the transformer bushings as a measure to mitigate their vulnerability under strong
seismic excitation. Finite element models of four different high voltage transformers were used
for performing modal and linear dynamic time history analyses in order to compare the response
of the bushing structures “as installed” and on a rigid base as well as investigate the efficiency of
several stiffening techniques to ensure the integrity of the bushings during strong earthquakes. In
addition, a two stage experimental investigation, consisting of system identification testing and
shake table testing, was conducted to verify the response trends identified by the numerical
studies.
Both numerical and experimental studies clearly showed that the bushing structures “as
installed” are very vulnerable to seismic excitation as well as very flexible compared to the ones
mounted on a rigid base. Moreover, these studies showed that stiffening the base of the bushings
can be beneficial for their response against ground shaking. From the stiffening techniques
investigated, incorporating flexural stiffeners on the cover plate of the transformer tank appears
to be the most efficient approach.
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Extreme Load Combinations: A Survey of State Bridge Engineers
Author: G. C. Lee, Z. Liang, J. J. Shen and J. S. O’Connor | Size: 15.8 MB | Format: PDF | Quality: Unspecified | Publisher: MCEER | Year: 2011 | pages: 156 | ISBN: 1520-295X
This report briefly describes the recent progress of the current research program at
MCEER sponsored by the Federal Highway Administration (FHWA) on the
establishment of multiple hazard design principles for highway bridges followed by a
more detailed discussion on one specific aspect of the study with respect to establishing a
limited number of extreme load combinations for detailed study. One of the primary
research tasks of the MCEER research program is to establish limit-state equations
involving multiple hazard load effects within the context of the Load and Resistance
Factor Design (LRFD) Specifications (AASHTO 2010), published by the American
Association of State Highway and Transportation Officials (AASHTO) (Lee et al, 2008).
This task compares the importance and design emphasis of the extreme loads as well as
extreme load combinations by investigating the current practice and issues in design. A
survey was conducted among the state bridge engineers that constitute AASHTO’s
Subcommittee on Bridges and Structures (SCOBS) to obtain their professional opinion
on design considerations that are appropriate for their region. The result is an important
reference for the establishment and simplification of extreme limit states.
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