The SF6 Decomposition Mechanism: Background and Significance

Gas Insulated Switchgear (GIS) has been widely used in substations. The insulating medium used in GIS is sulfur hexafluoride (SF6) gas. However, the internal insulation defect existed in GIS would inevitably lead to partial discharge (PD), and cause the composition of SF6 to SOF2, SO2F2 and SO2 and other characteristic component gases. The decomposition phenomenon would greatly reduce the insulation performance of SF6 insulated equipment, and even paralyze the whole power supply system. In this chapter, we first discuss the objective existence, decomposition mechanism and harmness of insulation defects. Then the methods for insulation defects detection used to avoid the insulation accidents are introduced. Comparing all of the detection methods, diagnosing the insulation defect through analyzing the decomposed gases of SF6 by chemical gas sensors is the optimal method due to its advantages, such as high detection accuracy and stability, signifying the importance of developing chemical gas sensor used in SF6 insulated equipment. In conclusion, there kinds of gas sensor material, carbon nanotubes, graphene, are chosen as the gas sensing materials to build specific gas sensors for detecting each kind of SF6 decomposed gases, and then enhance the gas sensitivity and selectivity by material modification

Polymer Composites for Electrical and Electronic Engineering Application

Polymer composite materials have attracted great interest for the development of electrical and electronic engineering and technology, and have been widely applied in electrical power systems, electrical insulation equipment, electrical and electronic devices, etc. Due to the significant expansion in the use of newly developed polymer composite materials, it is necessary to understand and accurately describe the relationship between composite structure and material properties, as only based on thorough laboratory characterization is it possible to estimate the properties for their future commercial applications. This book focuses on polymer composites applied in the field of electrical and electronic equipment, including but not limited to synthesis and preparation of new polymeric materials, structure–properties relationship of polymer composites, evaluation of materials application, simulation and modelling of material performance

The Effect of Atmospheric Aging on a Hybrid Polymer Matrix Composites\u27 Material Properties

Mechanical failure modes associated with elevated temperature exposure of the load bearing unidirectional hybrid composite (based upon glass and carbon fibers reinforcing a high temperature epoxy matrix) of a next generation transmission line design were investigated in this research. In particular, the flexural performance (in both static and fatigue loading) of the composite which had been exposed to elevated temperatures for prolonged periods of time was studied. To this end, a fatigue test was developed in an attempt to simulate the multi-axial loading conditions present on transmission lines. This test was used to evaluate the fatigue behavior of unaged specimens, as well as the evolution of fatigue performance of aged specimens. Furthermore, a four point loading configuration was used to assess the effect that aging had on the static flexure strength of the hybrid composite. It was found that the magnitude in static and fatigue material property reduction increased with aging time, and was dictated by which aging mechanism was dominant. Microstructural changes revealed that the modest reduction in mechanical properties at intermediate aging times was predominantly attributed to thermal oxidation, while for longer aging times physical aging was the primary cause for the substantial reduction. Finite element models were developed to quantify a newly discovered stiffening phenomenon observed in the composite subjected to fatigue. A mesh morphing scheme was developed to account for the scatter in the stiffening phenomenon due to the inherent geometric variability of the carbon fiber composite. In addition, 3-dimensional viscoelastic representative volume element finite element models were developed to understand the damage mechanisms of the hybrid composite system. Finally, the utility of waveform based broadband acoustic emission was explored to identify the types of damage which were occurring within the hybrid composite, as well as which material a particular mechanism originated from. To demonstrate the method as a potential in-service nondestructive evaluation technique, explicit dynamic finite element models simulating the 3 most common composite failure mechanisms (i.e. matrix cracking, fiber/matrix delamination, and fiber fracture) were developed. Based upon the spectral content of the simulated signals, a damage classification scheme based upon the method of Partial Powers was developed. The efficacy of the methodology was validated using waveforms captured during the quasi-static flexure testing of aged hybrid composite rods

Structure-Property Relationship of Nanomodified Mesophase Pitch-Based Carbon Fibers

Mesophase pitch-based carbon fibers are known for their excellent thermal and electrical conductivity, high tensile modulus, moderate tensile strength, but poor compressive strength. This collection of properties results from the texture and crystalline structure (together known as microstructure) of the fibers. Fiber microstructure, in turn, develops during processing due to the discotic nature of the mesophase pitch precursor. In prior studies, such important parameters as the size and shape of capillaries in the spinneret, spinning temperature and carbonization temperature have been varied to produce fibers with different microstructures and properties. In this dissertation, the primary research goal was to investigate how the microstructure and resulting transport properties of carbon fibers would be influenced by the incorporation of short aspect ratio multiwalled carbon nanotubes (MWCNTs) or, as a low-cost alternative, carbon black (CB) at ultra-dilute concentrations. Thus, MWCNTs and CB were dispersed into the mesophase pitch precursor at only 0.3 wt%. At this extremely low concentration, rather than acting as traditional fillers, these nanomodifiers served as surface-anchoring agents, which led to changes in the microstructure of the precursor and resulting carbon fibers. These microstructural modifications then impacted fiber and composite properties. In the first part of this study, the effect of nanomodification on fiber microstructure was evaluated. Using light and scanning electron microscopy, it was observed that the cross-section of unmodified (0 wt%) fibers had a well-defined radial texture, with minimal folding of the graphitic layers (average pleat length ~40 nm), especially for the large fraction (~83%) of fibers that exhibited “pac-man” type splitting. The cross-section of fibers modified with CB had a line-centered texture that exhibited increased folding of the graphitic planes (average pleat length ~30 nm) toward the outer surface of the fiber, resulting in ~45% of CB-modified fibers displaying “pac-man” splitting. Fibers modified with MWCNTs were found to have a largely random cross-sectional texture with significant folding of the graphitic planes (average pleat length ~30 nm) across the entire surface, and only ~3% of MWCNT-modified fibers showed “pac-man” splitting. Finally, via x-ray diffraction, it was determined that nanomodification had no adverse impact on crystallite size (Lc ~40 nm and La ~80 nm), orientation (FWHM ~2°), or graphitic perfection (d002 ~0.338 nm). This indicates that nanomodification could be a possible route for producing highly graphitic fibers, which are mechanically toughened by increased folding of the graphitic pleats. The second major component of this work focused on quantifying the density, electrical resistivity, thermal conductivity and mechanical properties of individual carbon fibers (i.e., single filaments). Using a set of calibrated cesium formate aqueous solutions, fiber densities were accurately measured to be 2.20 ≤ ρ0wt% \u3c 2.25 g/cm3, 2.15 ≤ ρMWCNT≤ 2.20 g/cm3, ρCB = 2.20 g/cm3. Thus, it was determined that external incorporation of nanomodifiers led to a small increase in percent void volume (~2%). This is consistent with a majority of literature studies that repeatedly show the undesired introduction of such voids with the incorporation of nanomodifiers. The single-filament electrical resistivity of the MWCNT-modified fibers (2.75±0.13 μΩ∙m) was not found to be significantly different (at a 95% confidence level) from the 0 wt% control (2.52±0.11 μΩ∙m); the CB-modified fibers only showed a slight increase in electrical resistivity (2.75±0.10 μΩ∙m). Similarly, fiber thermal conductivity (~550 W/m∙K) predicted from electrical resistivity values using the Issi-Lavin correlation showed no notable reduction as a result of nanomodification. Both nanomodified fibers showed a decrease in tensile strength (0 wt%: 1.71±0.21 GPa, MWCNT: 1.12±0.11 GPa and CB: 1.23±0.14 GPa) and modulus (0 wt%: 583±26 GPa, MWCNT: 520±26 GPa and CB: 527±30 GPa). Additionally, although a precise compressive strength for MWCNT- and CB-modified fibers could not be obtained (a result of limitations of the current tensile recoil testing method), all experimental fibers were determined to have a compressive strength of at least ~1 GPa. This is an improvement over previous studies. More notably, the difference in fiber structure achieved through nanomodification resulted in fibers with a better balance of compressive-to-tensile strength (σC/σT → 1), which is not observed for most highly conductivity conventional pitch-based carbon fibers. Another novel result from the present study is that the low-cost CB modifier was able to achieve similar changes in microstructure and properties as MWCNTs. In the final phase of this study, using both experimentation and finite element modeling, a method was developed to measure the bulk thermal conductivity of carbon fibers and their unidirectional composites. When applied to experimental fibers, no statistically significant difference in thermal conductivity was observed between MWCNT-modified (468±127 W/m∙K) and 0 wt% (514±179 W/m∙K) fibers. Additionally, these thermal properties were consistent with those predicted from single-filament electrical resistivity values (0 wt%: 569±18 W/m∙K, MWCNT: 533±20 W/m∙K). Thus, these types of composites could be useful as thermal management materials

Physics and Technology of Silicon Carbide Devices

Recently, some SiC power devices such as Schottky-barrier diodes (SBDs), metal-oxide-semiconductor field-effect-transistors (MOSFETs), junction FETs (JFETs), and their integrated modules have come onto the market. However, to stably supply them and reduce their cost, further improvements for material characterizations and those for device processing are still necessary. This book abundantly describes recent technologies on manufacturing, processing, characterization, modeling, and so on for SiC devices. In particular, for explanation of technologies, I was always careful to argue physics underlying the technologies as much as possible. If this book could be a little helpful to progress of SiC devices, it will be my unexpected happiness

Research and Technology, 1994

This report selectively summarizes the NASA Lewis Research Center's research and technology accomplishments for the fiscal year 1994. It comprises approximately 200 short articles submitted by the staff members of the technical directorates. The report is organized into six major sections: Aeronautics, Aerospace Technology, Space Flight Systems, Engineering and Computational Support, Lewis Research Academy, and Technology Transfer. A table of contents and author index have been developed to assist the reader in finding articles of special interest. This report is not intended to be a comprehensive summary of all research and technology work done over the past fiscal year. Most of the work is reported in Lewis-published technical reports, journal articles, and presentations prepared by Lewis staff members and contractors. In addition, university grants have enabled faculty members and graduate students to engage in sponsored research that is reported at technical meetings or in journal articles. For each article in this report a Lewis contact person has been identified, and where possible, reference documents are listed so that additional information can be easily obtained. The diversity of topics attests to the breadth of research and technology being pursued and to the skill mix of the staff that makes it possible

Nanoscale Ferroic Materials—Ferroelectric, Piezoelectric, Magnetic, and Multiferroic Materials

Ferroic materials, including ferroelectric, piezoelectric, magnetic, and multiferroic materials, are receiving great scientific attention due to their rich physical properties. They have shown their great advantages in diverse fields of application, such as information storage, sensor/actuator/transducers, energy harvesters/storage, and even environmental pollution control. At present, ferroic nanostructures have been widely acknowledged to advance and improve currently existing electronic devices as well as to develop future ones. This Special Issue covers the characterization of crystal and microstructure, the design and tailoring of ferro/piezo/dielectric, magnetic, and multiferroic properties, and the presentation of related applications. These papers present various kinds of nanomaterials, such as ferroelectric/piezoelectric thin films, dielectric storage thin film, dielectric gate layer, and magnonic metamaterials. These nanomaterials are expected to have applications in ferroelectric non-volatile memory, ferroelectric tunneling junction memory, energy-storage pulsed-power capacitors, metal oxide semiconductor field-effect-transistor devices, humidity sensors, environmental pollutant remediation, and spin-wave devices. The purpose of this Special Issue is to communicate the recent developments in research on nanoscale ferroic materials

Physical modeling of electrical conduction in printed circuit board insulation

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.Includes bibliographical references (p. 297-301).This thesis is concerned with understanding the degradation of electrical and electronic components in automobiles due to environmental effects. A special emphasis is placed on understanding the physical processes underlying the degradation, so that accelerated reliability tests can be specified with increased confidence of their validity. As a first case,printed circuit board (PCB) insulation was selected as a target for investigation. With an increase in the electronics and circuit miniaturization coupled with an increase in voltage in 42 volt as well as hybrid vehicles, PCB reliability has become an important issue. We first provide a broad presentation of insulation degradation theory as well as electrical conduction theory according to existing literature and then narrow our focus towards printed circuit board insulation. We develop a novel first-order mathematical model to describe electrical currents in printed circuit board insulation as a function of temperature, relative humidity, absorbed moisture content, voltage and geometrical characteristics. This model was developed from a series of experiments that were carefully performed under controlled laboratory conditions. In addition to describing the experimental procedure and results, we also explain the details of the experimental setup and measurement instrumentation. Furthermore, we present an intuitive physical explanations for some observations and model responses.by Vasanth Sarathy.S.M