Predicting Fault Transients on Underground Residential Distribution Systems - A Project of the Purdue Electric Power Center

This thesis addresses the problem of calculating and utilizing the voltage and current transients that may occur in underground residential distribution (URD) systems. A computational model for such systems is proposed and evaluated by comparisons to experimental results. The propagation characteristics of standard URD cables are complex but central to the computational model. The specific objective of this study was to determine whether a relatively simple approximation for the cable propagation constant is accurate enough that, when incorporated into the computational model for the transients resulting from a fault in the system, the resulting fault transient can be utilized to locate the fault. The conclusion is that over a frequency range of approximately 0.1 to 10 MHz, the computational model does provide a useful description of the transients. The approximation for the cable propagation constant does seem to provide adequate information about the variation with frequency of the phase constant and the attenuation constant when plausible ad hoc values of the parameters are included. The computational model is simple and quick to evaluate. It is based on standard lattice diagram analysis of the multiple reflections in the system. The model provides an approximation to the impulse response of the system, when the impulse is applied at various positions in the system

A. C. Power Losses in MOV Surge Arrestors

It was the objective of this study to measure power losses occurring in MOV surge arrestors as they were subjected to various voltage Excitations. In particular, power losses were observed in two MOV devices as sinusoidal voltages of different magnitudes were applied, at various frequencies in the range of typical power frequencies and common harmonics. Power losses were also observed in an MOV device for applied voltages consisting of the sum of 60 Hertz sinusoids and a single harmonic. The measurement procedure consisted of obtaining digital records representing the waveforms of voltage across and current through the MOV device during operation; power was calculated as the mean of the product of these digitally represented waveforms; This report contains a detailed description of the implementation of this procedure, as well as a discussion of some of its limitations when making measurements on highly reactive devices. Experimental results indicate that power losses in the MOV devices studied were primarily dependent upon frequency of operation, and peak amplitude of applied voltage. The results indicate that 60 Hertz specifications given for a particular device do not, in general, apply for other frequencies or non-sinusoidal excitation

Digital Measurement of Partial Discharge

Various new measurement techniques have been developed for a high voltage phenomenon referred to as partial discharge. Partial discharge is a localized breakdown of the high voltage insulation system which is observed as low level, random emissions. Both electrical and acoustic emissions have been measured in underground power cables, solid cast power transformers and in lumped specimens. Typical problems complicating the measurements are the randomness of the emission, high levels of interference and extreme distortion of the signal by the propagation path. Various signal processing techniques have been adapted to the measurement of partial discharge. The techniques investigated are capable of reducing noise in the measurements and have provided orders of magnitude improvement in sensitivity over ordinary methods. Some of the techniques studied are capable of providing information about the location of the partial discharge site

Description of the fluctuating colloid-polymer interface

To describe the full spectrum of surface fluctuations of the interface between phase-separated colloid-polymer mixtures from low scattering vector q (classical capillary wave theory) to high q (bulk-like fluctuations), one must take account of the interface's bending rigidity. We find that the bending rigidity is negative and that on approach to the critical point it vanishes proportionally to the interfacial tension. Both features are in agreement with Monte Carlo simulations.Comment: 5 pages, 3 figures, 1 table. Accepted for publication in Phys. Rev. Let

Circles in the Sky: Finding Topology with the Microwave Background Radiation

If the universe is finite and smaller than the distance to the surface of last scatter, then the signature of the topology of the universe is writ large on the microwave background sky. We show that the microwave background will be identified at the intersections of the surface of last scattering as seen by different ``copies'' of the observer. Since the surface of last scattering is a two-sphere, these intersections will be circles, regardless of the background geometry or topology. We therefore propose a statistic that is sensitive to all small, locally homogeneous topologies. Here, small means that the distance to the surface of last scatter is smaller than the ``topology scale'' of the universe.Comment: 14 pages, 10 figures, IOP format. This paper is a direct descendant of gr-qc/9602039. To appear in a special proceedings issue of Class. Quant. Grav. covering the Cleveland Topology & Cosmology Worksho

Bostonia: The Boston University Alumni Magazine. Volume 29

Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs

Unexpected drop of dynamical heterogeneities in colloidal suspensions approaching the jamming transition

As the glass (in molecular fluids\cite{Donth}) or the jamming (in colloids and grains\cite{LiuNature1998}) transitions are approached, the dynamics slow down dramatically with no marked structural changes. Dynamical heterogeneity (DH) plays a crucial role: structural relaxation occurs through correlated rearrangements of particle ``blobs'' of size $\xi$\cite{WeeksScience2000,DauchotPRL2005,Glotzer,Ediger}. On approaching these transitions, $\xi$ grows in glass-formers\cite{Glotzer,Ediger}, colloids\cite{WeeksScience2000,BerthierScience2005}, and driven granular materials\cite{KeysNaturePhys2007} alike, strengthening the analogies between the glass and the jamming transitions. However, little is known yet on the behavior of DH very close to dynamical arrest. Here, we measure in colloids the maximum of a ``dynamical susceptibility'', $\chi^*$, whose growth is usually associated to that of $\xi$\cite{LacevicPRE}. $\chi^*$ initially increases with volume fraction $\phi$, as in\cite{KeysNaturePhys2007}, but strikingly drops dramatically very close to jamming. We show that this unexpected behavior results from the competition between the growth of $\xi$ and the reduced particle displacements associated with rearrangements in very dense suspensions, unveiling a richer-than-expected scenario.Comment: 1st version originally submitted to Nature Physics. See the Nature Physics website fro the final, published versio

Sea Ice Thrust Structures

Unusual thrust structures in thin sea ice sheets were observed in Labrador and Greenland. These structures are the result of thin ice sheets being forced into each other by a combination of wind and waves. When thicker pack ice is subjected to these same forces pressure ridges result

Direct visualization of aging in colloidal glasses

We use confocal microscopy to directly visualize the dynamics of aging colloidal glasses. We prepare a colloidal suspension at high density, a simple model system which shares many properties with other glasses, and initiate experiments by stirring the sample. We follow the motion of several thousand colloidal particles after the stirring and observe that their motion significantly slows as the sample ages. The aging is both spatially and temporally heterogeneous. Furthermore, while the characteristic relaxation time scale grows with the age of the sample, nontrivial particle motions continue to occur on all time scales.Comment: submitted to proceedings for Liquid Matter Conference 200