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We compare different neural network architectures for Machine Learning (ML) algorithms designed to identify the neutrino interaction vertex position in the MINERvA detector. The architectures developed and optimized by hand are compared with the architectures developed in an automated way using the package "Multi-node Evolutionary Neural Networks for Deep Learning" (MENNDL), developed at Oak Ridge National Laboratory (ORNL). The two architectures resulted in a similar performance which suggests that the systematics associated with the optimized network architecture are small. Furthermore, we find that while the domain expert hand-tuned network was the best performer, the differences were negligible and the auto-generated networks performed well. There is always a trade-off between human, and computer resources for network optimization and this work suggests that automated optimization, assuming resources are available, provides a compelling way to save significant expert time.

Charged-current neutrino interactions with low hadronic recoil ("low-nu") have a cross-section that is approximately constant versus neutrino energy. These interactions have been used to measure the shape of neutrino fluxes as a function of neutrino energy at accelerator-based neutrino experiments such as CCFR, NuTeV, MINOS and MINERvA. In this paper, we demonstrate that low-nu events can be used to measure parameters of neutrino flux and detector models and that utilization of event distributions over the upstream detector face can discriminate among parameters that affect the neutrino flux model. From fitting a large sample of low-nu events obtained by exposing MINERvA to the NuMI medium-energy beam, we find that the best-fit flux parameters are within their a priori uncertainties, but the energy scale of muons reconstructed in the MINOS detector is shifted by 3.6% (or 1.8 times the a priori uncertainty on that parameter). These fit results are now used in all MINERvA cross-section measurements, and this technique can be applied by other experiments operating at MINERvA energies, such as DUNE., 18 pages, 10 figures, Replaced with accepted version

We present methods to fabricate high-capacity redox electrodes using thick membrane or fiber casting of conjugated polymer solutions. Unlike common solution casting or printing methods used in current organic electronics, the presented techniques enable production of PEDOT:PSS electrodes with high charge capacity and the capability to operate under applied voltages greater than 100 V without electrochemical overoxidation. The electrodes are shown integrated into several electrokinetic components commonly used in automated bioprocess or bioassay workflows, including electrophoretic DNA separation and extraction, cellular electroporation/lysis, and electroosmotic pumping. Unlike current metal electrodes used in these applications, the high-capacity polymer electrodes are shown to function without electrolysis of solvent (i.e., without production of excess H+, OH-, and H2O2 by-products). In addition, each component fabricated using the electrodes is shown to have superior capabilities compared with those fabricated with common metal electrodes. These innovations in electrokinetics include a low-voltage/high-pressure electroosmotic pump, and a "flow battery" (in which electrochemical discharge is used to generate electroosmotic flow in the absence of an applied potential). The novel electrodes (and electrokinetic demonstrations) enable new applications of organic electronics within the biology, health care, and pharmaceutical fields.

For high temperature wire enamel application, the dielectric properties of nanoscale silica and alumina filled polyamideimide were characterized as a function of filler loading, and temperature. It was found that although the dc breakdown strength improved for both composite systems, only the alumina also exhibited an increase in ac breakdown strength. In addition, the voltage endurance at elevated temperature in both a needle/plate and twisted wire geometry was improved over a narrow range of filler loading (5-7.5 wt%). At room temperature, pulsed electroacoustic analysis (PEA) data does not indicate any difference in space charge buildup in the composite for fields up to 25 kV/mm over a period of 2 h. This is in contrast to other nanocomposite systems, which tend to show mitigation of space charge buildup with the addition of nanoparticles. Dielectric spectroscopy shows that the addition of nanoparticles increases the real permittivity above that expected for volumetric mixing rules. This enhancement is associated with high effective permittivity interfacial areas. No systematic changes in losses in the frequency range between 10-4 and 105 Hz were seen. The results suggest that carrier scattering is the primary mechanism leading to the improved breakdown strength.

High aspect ratio fillers are predicted to increase the dielectric constant of polymer composites more efficiently than spherical fillers according to the rule of mixtures. Using high aspect ratio fillers is a promising route for creating high dielectric constant, low loss materials at a low filler volume fraction, for use as capacitor and electric field grading materials. In this work, two high aspect ratio fillers were mixed into a polymer matrix, and the dielectric properties of composites were studied. Barium titanate fibers were synthesized by electrospinning a sol-gel, followed by a heat treatment to obtain a perovskite crystal structure. The heat treatment conditions were found to be crucial for obtaining tetragonal barium titanate fibers with high dielectric constant. Graphene platelets were prepared by a thermal shock method, which was found to result in a larger dielectric constant. A combination of barium titanate and graphene platelets yielded the highest dielectric constant when used in a polydimethyl siloxane matrix. The increase in dielectric loss over the pure matrix was small when the volume fraction was below the percolation threshold of graphene platelets. Electric flux density-electric field (D-E) measurements showed a linear dielectric constant in barium titanate filled composites and higher loss when graphene was added. The ac breakdown strength was reduced compared to the neat polymer and was affected by filler aspect ratio. The mechanisms that lead to the observed phenomena are discussed.

Study of the experimental literature regarding nanodielectrics indicates numerous inconsistencies in the results obtained. In many cases, the likely cause is due to a lack of quality control during nanocomposite processing. By examining examples from the literature along with an alumina/polyamideimide nanocomposite and silica/crosslinked polyethylene nanocomposite, this contribution seeks to shed light on some of the likely causes for these inconsistencies. Measurements of the dielectric breakdown strength and voltage endurance confirm that poor dispersion can lead to poor material performance and the use of quantitative techniques is highlighted. Good dispersion alone is not sufficient to achieve improved properties. The addition of nanoparticles can alter the resulting structure of the nanocomposites, can introduce water into the system resulting in cavity formation and can also result in degradation of the polymer if the processing parameters are not carefully selected. In this review, understanding the effects of nanoparticle addition requires not only characterization of relevant dielectric properties, but also careful control of the processing parameters and characterization of changes in polymer structure, particle dispersion, and water content.

It is well known that hopping of charge carriers via spatially and energetically distributed localized states is a primary transport mechanism in many disordered semiconductors and polymeric dielectrics. In this contribution, the nonlinear I-V physics of a 25 vol% 50 nm p-SiC/silicone rubber composite for high voltage field grading application was investigated, and a composite bulk hopping mechanism proposed. It is hypothesized that nearest-neighbor hole hopping occurs through thin rubbery layers between the SiC particles, and is the mechanism governing the nonlinear electric response of SiC/silicone rubber nanocomposites.

Research on the vacuum surface flashover mechanisms of insulating material under nanosecond pulses is important for the design and manufacture of high-power pulse generators. Here, the vacuum surface flashover characteristic of epoxy composites filled with different microfillers Al2O3 middot3H2O , Al2O3, BaTiO3, and TiO2 is investigated using a unipolar pulse generator (50-ns rise time and 600-ns full-width at half-maximum). In addition, their thermally stimulated depolarization current and secondary electron emission (SEE) coefficients are measured. The results show that the flashover performance does not depend just on the SEE coefficient, but that the different effects of shallow and deep traps must also to be taken into account.

Polymer nanocomposites with metal oxide nanoparticle fillers exhibit enhanced electrical breakdown strength and voltage endurance compared to their unfilled or micron filled counterparts. This paper presents the following hypothesis for the mechanisms leading to improved properties. The inclusion of nanoparticles provides myriad scattering obstacles and trap sites in the charge carriers' paths, effectively reducing carrier mobility and thus carrier energy. The result is homocharge buildup at the electrodes, which increases the voltage required for further charge injection due to blocking by the homocharge. The hypothesis is supported by electroluminescence, pulsed electro acoustic analysis, thermally stimulated current measurements, a comparison of AC, DC, and impulse breakdown, as well as absorption current measurements, in silica/crosslinked polyethylene matrix composites with supporting evidence from titania/epoxy composites.

Electron paramagnetic resonance (EPR) has been used to study the properties of trapped electrons or holes in XLPE and in 12.5% vinylsilane-treated SiO2 nano-particles in XLPE specimens. Both electrically unstressed and electrically stressed (up to 25 kV/mm) specimens were used. The EPR spectra of both materials indicated that the acceptors/donors were oxygen radicals in the polymer, probably originating during the cross-linking. It was found that the anisotropic oxygen environments were not randomly oriented, but were textured, presumably during the fabrication of the sheet specimens. It was found that under the action of an applied electric field, the population of an additional number of oxygen radicals occurred. This result is discussed in relation to the implied polymer structure and conductivity mechanisms.

This paper presents and verifies a new mathematical model to explain the dynamic behavior of characteristic gases in the oil-cellulose insulation of high voltage devices like power transformers. The model is based on the diffusion process. Parameters of the model are already quantified from experiments and presented in previous publications. The mathematical model and assumptions are presented here. The model solution is obtained analytically and gas concentration change inside the paper insulation as a function of time is simulated. The results are converted to the concentration change in the oil using the principle of conservation of mass and validated with experimental measurements. The presented model can be used to reduce the error of dissolved gas analysis due to the migration of characteristic gases inside a healthy power transformer.

Dissolved gas analysis (DGA) is a well established method to monitor and predict the condition of devices with oil-cellulose insulation, especially power transformers. However, the effect of the migration of theses gases between the liquid and solid insulation is often ignored. The migration phenomenon is temperature dependent and, if ignored, can potentially lead to erroneous condition assessment by the DGA method. This paper addresses the dynamic nature of propagation of these gases in such systems based on temperature variations. Diffusion times, and therefore diffusivity of the gases, in oil-impregnated cellulose are calculated by identifying the diffusion process as a linear system. The diffusion time-constants, and steady-state condition at the working concentrations, are estimated based on the identified model. A sensitivity study is performed to show the dependency of the diffusion time-constants to the temperature and the oil-cellulose ratio in the system. The equilibrium curves are obtained in the case of carbon dioxide by using solubility information of this gas in the oil and paper pulp, similar to the case of moisture equilibrium. The results are compared with the experimental data. An example of the implication of the obtained data is shown

Transformer oil/cellulose structures are often designed based on a cumulative stress criterion derived from experimental tests at power frequency. However, such structures must also meet stringent impulse requirements defined by a basic insulation level (BIL). The industry has tried to establish an equivalence factor to permit power frequency cumulative stress methods to be used to estimate impulse withstand strength. Since the mechanisms of failure differ substantially under surge conditions, there would seem no good reason to suppose that a universal equivalence factor is appropriate. Tests are reported using a 2.3 MV generator to document impulse failure of a number of bulk, creep and hybrid structures to establish the nature of this relationship through statistical comparisons with the established 50/60 Hz methods. Factors varied from 1.94 to 3.34, depending on the configuration. The methodology is described and the results discussed in the context of the design of oil-cellulose structures, having regard to complicating factors such as waveshape and electrode covering. The study permits some speculation about impulse design under hybrid situations (i.e. failure paths involving both creep and bulk liquid)

The formulation and computation of an optimal load shedding time algorithm is presented. This new concept was developed as an enhancement to the application of optimal load shedding for corrective control to support future islanded power systems with anticipated, enhanced communications infrastructure. The methodology combines nonlinear mathematical programming and discretized differential-algebraic power systems equations to estimate the optimal amount of load to be shed as well as the best time to shed it. Several simulated scenarios are studied and results presented.

The incorporation of silica nanoparticles into polyethylene increased the breakdown strength and voltage endurance significantly compared to the incorporation of micron scale fillers. In addition, dielectric spectroscopy showed a decrease in dielectric permittivity for the nanocomposite over the base polymer, and changes in the space charge distribution and dynamics have been documented. The most significant difference between micron scale and nanoscale fillers is the tremendous increase in interfacial area in nanocomposites. Because the interfacial region (interaction zone) is likely to be pivotal in controlling properties, the bonding between the silica and polyethylene was characterized using Fourier transformed infrared (FTTR) spectroscopy, electron paramagnetic resonance (EPR), and x-ray photoelectron spectroscopy (XPS). The picture which is emerging suggests that the enhanced interfacial zone, in addition to particle-polymer bonding, plays a very important role in determining the dielectric behavior of nanocomposites.

The incorporation of nanoparticles into thermosetting resins is seen to impart desirable dielectric properties when compared with conventional (micron-sized particulates) composites. Although the improvements are accompanied by the mitigation of internal charge in the materials, the nature of the interfacial region is shown to be pivotal in determining the dielectric behaviour. In particular, it is shown that the conditions and enhanced area of the interface changes the bonding that may give rise to an interaction zone, which affects the interfacial polarization through the formation of local conductivity.

The utility of condition monitoring of the stator insulation structure of large machines has been enhanced substantially by the use of computer-based analysis of partial discharge signatures. A number of indices are examined through tests in a multistress aging facility to assess their promise in describing insulation degradation in machine insulation. In transitioning such tests to the field environment, an operational test is also described which offers some promise in identifying degradation without prior baseline data for a machine. On the basis that most electrical failures have mechanical precursors, acoustic methods are described for assessing stator bar mechanical integrity. This includes both using the conductors as waveguides and also employing acoustic emission for the location of large discharges.

The incidence of streaming electrification in large transformers (and other industrial equipment) has generated the need for both an understanding of the underlying physics and a mathematical description of the phenomenon. Modeling is needed since the mechanisms do not readily scale and small-scale laboratory experiments are limited in predicting performance. The development of both steady-state and transient descriptions of the streaming electrification process is described for a rectangular duct structure. The nature of the phenomenon is such that appropriate assumptions and approximations need to be made. As a consequence, some experimental verification of the outcomes, at least in qualitative form, is also included. The entrainment of charge from the interface charge layers also intimately involves the flow of the liquid. A description of the flow regimes and a transient solution of the charge development through a duct are thus an integral part of the modeling effort. The utility of the steady-state model developed is demonstrated by application to an oil-cellulose system typical of a large core-form transformer. The method advocated takes advantage of the repeat duct arrangement in such units. The results presented allow the internal behavior of such a unit to be studied in considerable depth, and provide insight into the complex interplay between generation and relaxation in circumstances when flow rates, temperature, external fields and influent charge are changed.

After a brief discussion on possible on-line indicators of aging, this paper presents a concept of dynamic aging theory (DAT). Based on the philosophy of a DAT, a dynamic multistress aging model is proposed. Necessary DAT formulation and software have been developed for testing the model against laboratory aging data. In this study, dynamic stagnation voltage (DSV), a derived partial discharge parameter, and the groundwall insulation response to a traveling acoustic wave have been found to be the most appropriate parameters for assessment of remaining insulation machine life. This approach is shown to be a meaningful and practical solution to a very complex problem. Although this study is in its initial stage, it does show significant promise as an on-line tool for dynamically predicting remaining life based on DAT and other appropriate feedback measures.

An experimental study has been conducted to quantify the voltage endurance of electrical grade epoxy resin insulation when subjected to pulse voltages in a divergent field. Voltage endurance has been quantified as a function of pulse width, repetition rate, and polarity. Supporting measurements of free radical generation have been made by electron paramagnetic resonance (EPR), and the progress of the aging mechanism tracked by sensitive photonic emission measurements. The results suggest (at least for positive polarity) that estimates of endurance under pulse voltage conditions can be made from conventional power frequency data, However, it is shown that a correction is necessary to allow for the effects of waveform, and a theory is advanced for that purpose.

We report on test results for a single phase, 60-Hz, 13.8 kV/6.9 kV, 1-MVA high temperature superconducting (HTS) transformer which was completed in February, 1998. This transformer models in many ways a full scale section of a 30-MVA HTS commercial transformer design. The transformer windings are cryocooled in the range of 25 K and are made with a low-cost, surface-coated BSCCO-2212 conductor. Heat leaks are reduced using a liquid nitrogen thermal ballast and reservoir. The use of high temperature superconductors can substantially reduce transformer losses, weight, size, noise and potential fire and environmental hazards. Designs promise stable operation through faults without thermal degradation, and at temperatures that allow efficient and reliable refrigeration.

Streaming electrification occurs in large power transformers when oil circulated for cooling purposes acts to separate charges from the Debye layer on the cellulose insulation surfaces. This phenomenon is believed to have caused several catastrophic transformer failures and remains to be satisfactorily understood in realistic geometries. A network-based streaming electrification model is presented which utilizes single winding ducts as the basic element to investigate a core-form structure. The network is first analyzed using hydraulic duct parameters to calculate the oil flow distributions within the structure. This data is then provided to the electrification solver which predicts the charge densities at each duct outlet. The charge density results are ultimately used to determine the streaming potentials at each node based on an a suitable matrix of leakage resistances. Development of the network model is presented along with empirically-based calibration data for a realistic section of core-form transformer geometry.

In an effort to understand the dynamic behaviour of the streaming electrification phenomenon better, a computational model has been prepared. This paper describes the development and behaviour of the simulation for the development of charge-density profiles in space and time subsequent to the initiation of flow in a channel. Results are provided to demonstrate the functionality of the model and its effectiveness in clarifying the nature of the phenomenon.

Streaming electrification occurs in large power transformers where insulating oil circulated for cooling purposes acts to separate charge from the interfacial double layer present on a multitude of cellulose insulation surfaces. In this paper, the electrification phenomenon is addressed from a microscopic viewpoint. An empirically calibrated analytical model is provided for calculating the amount of charge separated in a core-form transformer duct. The model incorporates a boundary layer approach in approximating the wall charge distribution which provides a critical length scale for the analysis. This length scale is used to specify the appropriate model for charge development under turbulent flow conditions. The duct model considers both laminar and turbulent flows subject to ac electric fields and varying temperature. This concept forms the elemental building block of a network-based methodology for examining electrification in a complete transformer geometry.

Recent experimental and field studies of streaming electrification have shown that transient phenomena can be of paramount importance in the distribution and accumulation of charge. Unlike most previous steady-state analyses, the development of a transient model has permitted some of the complex interactions to be isolated and understood. The results of exercising this model here have clarified the dependency on operational, geometric, and chemical parameters, and provide significant insight into the physical and chemical behavior which underlies the electrification process.

We have observed two new decay modes of the charmed baryon $\Xi_c^+$ into $\Sigma^+ K^-\pi^+$ and $\Sigma^+ \bar{K}^{*0}$ using data collected with the CLEO II detector. We also present the first measurement of the branching fraction for the previously observed decay mode $\Xi_c^+\to\Lambda K^-\pi^+\pi^+$. The branching fractions for these three modes relative to $\Xi_c^+\to\Xi^-\pi^+\pi^+$ are measured to be $1.18 \pm 0.26 \pm 0.17$, $0.92 \pm 0.27 \pm 0.14$, and $0.58 \pm 0.16 \pm 0.07$, respectively.

The construction of an apparatus for the measurement of the electrostatic charging tendency (ECT) of a dielectric liquid is described. A sealed reciprocating piston arrangement permits a liquid to be repetitively passed through a charge separating element. The use of a gold element is shown to minimize the effects of moisture and control temporal effects. The system is evaluated by testing samples of transformer oil drawn from the field. In general, the new system ranks the oils in the same way as a conventional assessment against a paper filter, although anomalies have been found which are an impediment to adoption.

The use of optical multichannel analysis is described to quantify the establishment of corona in a positive point/plane electrode gap for 50/50 SF6 /N2 gas mixtures. The system permits spatial and temporal resolution of the emitted light and, in conjunction with other measurements, provides evidence on the mechanism of corona stabilization for a range of pressures and step voltages up to breakdown. On the basis of the optical results a tentative model is advanced based on the establishment of a collaborative streamer cloud from which individual streamers emanate. Aspects of this work call into question the true interpretation of the critical pressure.

We have measured the weak decay asymmetry parameters ($\aLC $) for two \LC\ decay modes. Our measurements are $\aLC = -0.94^{+0.21+0.12}_{-0.06-0.06} $ for the decay mode $\Lambda_c^+ \to \Lambda\pi^+ $ and $\aLC = -0.45\pm 0.31 \pm 0.06$ for the decay mode $\Lambda_c \to \Sigma^+\pi^0 $. By combining these measurements with the previously measured decay rates, we have extracted the parity-violating and parity-conserving amplitudes. These amplitudes are used to test models of nonleptonic charmed baryon decay.

Graphene oxide filled silicone rubber nanocomposites were found to possess a large nonlinear coefficient of electrical conductivity, smaller low field conductivity than that of the neat polymer and an increase in the dielectric constant over that of the polymer matrix with a very small increase in the dielectric loss. These electrical and dielectric properties make graphene oxide/silicone nanocomposites an excellent candidate for a field grading material. Possible mechanisms that lead to the observed dielectric behavior are discussed in this work. The effect of sample size and processing on the material properties is also discussed.

The properties of nanodielectrics have been shown to be critically dependent on the way in which the materials are formulated. Large scale agglomeration often has disastrous effects on the resultant properties when conventional techniques are used to prepare the materials. In particular, the dispersion of the nanophase material has been shown to be critical. This contribution seeks to examine the impact of a new technique which involves the formation of the nanoparticles in situ through a process of gaseous infusion. The resulting materials are characterized, and some preliminary electrical properties are documented which would indicate some promise, although there are some restrictions.

We have studied the leptonic decay of the $\Upsilon (1S)$ resonance into tau pairs using the CLEO II detector. A clean sample of tau pair events is identified via events containing two charged particles where exactly one of the particles is an identified electron. We find $B(\Upsilon(1S) \to \tau^+ \tau^-) = (2.61~\pm~0.12~{+0.09\atop{-0.13}})%$. The result is consistent with expectations from lepton universality.

The morphology of cellulose acetate/poly(methyl methacrylate), CA/PMMA, blends of various compositions was studied. Optical microscopy and DSC conclusively showed that the polymers form incompatible blends. However, partial miscibility between the phases was noted since the glass transition temperature of the PMMA phase increased with the increase in the amount of the CA fraction in the blend, while the glass transition temperature of CA decreased with the increase in the amount of the PMMA fraction in the blend. ATR-FTIR spectra and surface energy measurements showed that the CA/PMMA film surfaces were comprised primarily of PMMA polymer. These results suggest that the CA/PMMA blends form a layered morphology with surface layers comprised essentially of PMMA polymer and the interior layer comprised of phase-separated blend. He, O 2 gas transport properties of CA, PMMA and CA/PMMA blends of several compositions have been measured at 35°C. The data were analyzed in terms of parallel and series resistance models. The high He/O 2 and He/N 2 gas separation factors were best described by a combination of the parallel and series models that is consistent with the proposed layered film morphology. A novel composite gas separation membrane was prepared by coating porous polysulfone hollow fibers with a solution of the CA.PMMA blend. CA/PMMA composite hollow fiber membranes with a broad range of coating thicknesses were prepared and their He and N 2 gas transport properties were measured. The properties were compared to the gas transport properties of the CA and PMMA composite hollow fiber membranes of equivalent coating thicknesses. The CA/PMMA composite membranes exhibited a superior combination of He/N 2 gas separation factors and He permeation rates compared to the CA or PMMA composites. The superior properties were attributed to the unique layered morphology of the coating comprised of PMMA exterior layer and mostly CA interrior layer. The formation of layered morphology was supported by surface energy measurements. The surface energy of the CA/.PMMA composite hollow fiber membrane was measured and found to be essentially identical to that of the PMMA polymer. The multilayer coating morphology was observed directly under SEM examination of the hollow fiber cross sections. CA/PMMA composite membranes can be used to purify helim gas streams to produce a high purity product (less than 10 ppm contaminant level) with high helium recovery in a single-stage process.

The behavior of transformer oil and other dielectric fluids used for the cooling and insulation of power system equipment is significantly influenced by motion enforced by the action of circulating pumps. Two important factors impact the situation. First, charges generated by streaming electrification in critical parts of the hydraulic circuit having high velocity and/or turbulence can accumulate to distort the electric field in positions where dielectric integrity is prejudiced. However, the dielectric strength of the fluid is also altered per se by the actions of the flow in a complex, but predictable, manner. Both of these aspects need to be understood to permit informed design, operation and monitoring of forced-cooled equipment. >

Many of the electrical failures of large electric machines have mechanical precursors. This premise has led to the attempts described here to detect mechanical changes, such as groundwall delamination, by acoustic methods as a means of early detection of incipient failure. By optimally launching an ultrasonic wave into a stator bar and using the conductor as a waveguide, it has been shown possible to interrogate the groundwall insulation and the critical interface region adjacent to the conductor. Laboratory studies using an epoxy mica stator bar subjected to thermal cycling have demonstrated that the acoustic signatures obtained with this method are mirrored by conventional corona spectroscopy conducted simultaneously, although earlier damage is clearly discernible. Based on the results of this study, the acoustic technique appears to have substantial promise as an advanced detection tool. >

Based on the physical mechanisms believed to underlie the ac electrical breakdown of liquid/solid structures, a volume theory of failure is used to justify the application of a semi-empirical cumulative stress criteria for the assessment of dielectric integrity. The method advocated is extended through the use of a complex Laplace equation to permit the analysis of structures having simultaneous capacitive and resistive stress distributions. Computer algorithms are described for automating dielectric design on this basis and case studies provided to illustrate the utility of the techniques advanced. >

This paper examines the hydrothermal aging of XLPE/silica nanocomposites. Nanocomposites are exposed to humid environment with a relative humidity of 100 % at 50 °C and the changes in moisture diffusion and electrical strength are investigated. In addition to moisture decreasing the electrical performance of nanocomposites somewhat, there is evidence that moisture can permanently damage the nanocomposites.

Moisture is known to influence the electrical performance of polymers. The introduction of nano particulates creates numerous additional pathways which radically affect the migration of moisture in nanocomposite materials. In this paper, cross-linked polyethylene/silica nanocomposites at loadings of 5 wt% and 12.5 wt% of both unfunctionalized and vinylsilane-functionalized nano silica were exposed to humid environments at elevated temperature. Nanocomposites were found to have a much higher moisture uptake compared to cross-linked polyethylene base resin. The dielectric properties of these hydrothermal conditioned samples were characterized by breakdown strength measurements, pulsed electro-acoustic analysis, and dielectric spectroscopy. A close relationship between particle loading, moisture uptake and dielectric properties was found, which provides important evidence that determining the optimal particle loading of nanodielectrics should take moisture influence into account.

Composite polymer materials containing a wide array of micron-sized fibers, flakes, and particles have provided improvements in non-electrical properties, such as hardness, thermal expansion, abrasion resistance, weight, and cost. However, when applied as solid dielectrics, these composites often display some degradation in electrical performance, when compared with their unfilled counterparts. In recent years, nanocomposites (i.e., composites with fillers smaller than 100 nm) have been shown to possess many of the same improvements without the associated decrease in electrical insulation properties. In fact, many nanofilled systems demonstrate electrical properties (e.g., dielectric breakdown strength and voltage endurance) that are improved over unfilled resins. It is believed that these improvements in nanodielectrics stem from the relatively large volume fraction of interfacial region between the filler and polymer matrix, where local properties such as density, conductivity, and chain mobility are modified by the presence of the inclusions. In this chapter, consideration is given to local and bulk properties due to loading of the host matrix with nanoparticles.

Long-time accelerated aging tests in a laboratory environment have been conducted on generator stator insulation to identify meaningful diagnostic measures for the assessment of degradation and identification of aging mechanisms. A plurality of techniques are investigated and diagnostic parameter, the dynamic stagnation voltage, which appears to be correlated with delimination in the epoxy-mica structure, is proposed. The results provide a basis for an online interpretation method for insulation condition. >

CLEO has observed a signal corresponding to the previously unseen decay ξ c 0 →Ω − K + . The observation of this decay mod points to W-exchange diagrams being an important contributor to the decays of the ξc0.

In recent years, the availability and low cost of nanometric-sized filler particles have generated great interest in polymer nanocomposites for a host of applications, including electrical insulation with enhanced breakdown and voltage endurance properties. This work combines the results of several experiments to add insight to the processes taking place in the crucial polymer transition region near the particle surfaces. The relative tendency to accumulate space charge under a high DC field is investigated through pulsed electroacoustic (PEA) apparatus. DC transient (absorption) currents reveal a quasi-DC conductivity that is surprisingly high in the nanocomposite, a result that is reinforced by dielectric spectroscopy, which also indicates a reduction in the nanocomposite's real permittivity. Thermally-stimulated currents reveal the presence of shallow traps that accompany the nanoparticle inclusions. Taken together, the results of the study indicate that the transition region is responsible for the desirable nanocomposite bulk properties which are today of interest, and help explain the difference in performance between these new materials and both unfilled resin and conventional composites composed of micron-sized fillers.

It has been shown that in many cases, the addition of nanoscale metal oxide fillers to polymers leads to an improvement in dielectric breakdown strength at room temperature. However, in some cases electrical insulation is exposed to elevated temperatures. A thermally stable polymer material, such as polyamideimide (PAI), is desired for these applications. For this reason, breakdown strength measured at elevated temperatures is required, since this property is expected to degrade with an increase in temperature. The addition of nanoparticles has been shown to increase PAI decomposition temperature and is also expected to mitigate the effect of increased temperature on dielectric properties. In this paper, AC and DC breakdown strength of PAI and nanosilica filled PAI are reported at room temperature and elevated temperatures. (200–340°C) Test temperatures were well below the decomposition range of polyamideimide as measured by thermogravimetric analysis (TGA). Silica composites at all loadings (whether treated or untreated) were shown to have a higher AC and DC breakdown strength at elevated temperatures than unfilled material. Dielectric spectroscopy results are also presented.

Intentional islanding (referred to a micro-grid) holds promise to improve power system reliability and power quality due to its more flexible control. To operate intentional islanding successfully, more efficient and robust control methods are required. A new concept is developed as an enhancement to the application of optimal load shedding for corrective control to support an islanded power system. The new proposal is comprised of two major stages in which one nonlinear optimization problem and one linear integer optimization problem are formulated. Numerical simulations conducted on a 15-bus system have demonstrated the performance of the new algorithm.