Dissertation/Thesis Abstract

Evaluation and protection of high voltage electrical equipment against severe shock and vibrations
by Kong, Dohwan, Ph.D., State University of New York at Buffalo, 2010, 476; 3423577
Abstract (Summary)

In recent moderate and strong seismic events, it was demonstrated that parts of the electrical power system are vulnerable to damage and their performance is strongly influenced by specific equipment design and installation practice. Some of the most complex and vulnerable components are: (i) disconnect switches and (ii) high power transformers. Each of these components has vulnerable parts which should be studied, evaluated and possibly protected in order to ensure continuous operation after earthquakes. This dissertation focuses on the two systems indicated above.

A disconnect switch used in substations of large electrical grids is an important component that supports the functionality of the electrical network. Such a switch is a combination of a support structure and the switching mechanism, which in turn is made of fixed and moving metal parts and of ceramic, or composite, electrical insulators. In order to determine if this equipment is acceptable in seismic areas, the static and dynamic characteristics of these high voltage three-phases disconnect switches and their capacity to withstand severe vibrations testing has to be performed. Due to the complexity of such systems and uncertainties in the construction and behavior of components, such determination cannot be done computationally.

In an attempt to determine contributions of components to the global response of the disconnect switch (DS) systems, this work proceeds with a methodical experimental and computational study. Tests to find the characteristics of each component were performed first, followed by tests of various subassemblies. Moreover, the entire assembly was also tested while observing the contributions of the individual components and sub-assemblies. When weak components were identified, a solution for protecting the components through modification of the response of the global system was attempted. The test results and the numerical evaluations showed several important characteristics in the behavior of the disconnect switches and issues in their acceptance testing (qualifications): The adequacy and acceptance of transformers and transformer bushings, is of great concern in the electrical industry. The current practice such as the IEEE 693-2005 recommends the following about the qualification tests of a transformer bushing: (i) using a rigid frame to hold the bushing on a shake table instead of using a real transformer tank and (ii) doubling input ground motions to consider the amplification of the ground motion caused by the flexibility of the transformer tank. The rigid frame lacks the capability to simulate the dominant effects of the local connectivity of the bushing to the transformer’s cover, while the base motion recommended by the current code underestimates the effects of the influence of the tank walls and cover plate on the motion transmitted to the bushing at its connection to the tank. While a bushing is mounted on the roof (cover) of a transformer tank, the excitation transmitted to the bushing is not identical to the ground motion below the transformer tank. The roof motion is amplified (or attenuated) differently in the horizontal and vertical directions due to the dynamics of the tank. This study identifies the issues related to the acceptance testing and proposes, designs, develops, and evaluates experimentally and numerically a support frame simulating transformer behavior.

Due to limitations in reproducing simulated earthquake ground motions, seismic qualification testing is often limited to lower levels of shaking. In this study, the possibility of using a modulated sinesweep that can be implemented in smaller laboratories as an input base motion for qualification purposes is investigated. The sine-sweep proposed is modulated to match an arbitrary required response spectrum for electrical equipment (such as required by IEEE 693 RRS).

In addition to the existing methods to identify system frequencies and damping values specified in testing standards, an alternative method, i.e. a table impulse test, is developed and evaluated by analyzing testing results. A table impulse test can share most of advantages which can be found from the existing resonant frequency search test methods, while each existing method shares only one or some of those advantages. (Abstract shortened by UMI.)

Indexing (document details)
Advisor: Reinhorn, Adrei M.
Commitee: Filiatrault, Andre, Mosqueda, Gilberto
School: State University of New York at Buffalo
Department: Civil, Structural and Environmental Engineering
School Location: United States -- New York
Source: DAI-B 71/11, Dissertation Abstracts International
Subjects: Civil engineering
Keywords: Base isolation, Disconnect switch, High voltage electrical equipment, Seismic evaluation, Severe shock, Sine sweep, Table impulse, Transformer bushing, Vibrations
Publication Number: 3423577
ISBN: 978-1-124-24616-1
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