Reduction In Breakdown Strength Research Articles

Evaluation of aging in nanofilled polypropylene by surface discharges

Literature indicates conflicting results on improvement/degradation of electrical characteristics due to introduction of nanofillers into polymers. Since polypropylene has superior electrical, mechanical and thermal properties and has significant utility in electrical industry, this work investigates the effect of nanofiller content on the partial discharge resistance and breakdown strength of the polypropylene films with 0%, 2% and 6% organoclay nanofillers. Since the surface discharges are random in nature, the overall partial discharge behavior is quantified in terms of temporal behavior of the Weibull parameters of the partial discharge pulse amplitude spectra obtained during sample aging and analyzed within the framework of time series analysis. Experiments indicate that the partial discharge characteristics are affected by the percentage of nanofiller content. Microscopic examinations indicate that on exposure to aging by partial discharges, the defect volume decreased in nanofilled polymer and was found to be least in samples where nanofiller content was below the percolation threshold. Profilometric studies indicate that the partial discharge resistance increases with increase in filler content. Results indicate that in fresh unaged samples, the breakdown strength improves with nanofiller content. However, the reduction in breakdown strength due to aging in nanofilled samples is noticeably higher as compared to unfilled samples.

Synthesis and characterization of epoxy-aluminum nanocomposites for energy storage applications

In this paper, electrical properties of nanocomposites made of epoxy resin filled with oxide coated aluminum particles are investigated. Nanocomposite samples were prepared and experiments were performed to measure the dielectric properties including breakdown strength with respect to different filler concentrations. Material characteristics were analyzed using Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD) and Thermogravimetric (TGA) techniques. Maximum electric energy density in the epoxy nanocomposite dielectric material was evaluated for different filler concentrations and compared with that of pure epoxy. Both large permittivity and high breakdown strength are required for large electric energy storage. The addition of nanoparticles enhanced the permittivity and resulted in potential gain in electric energy density even if there is slight reduction in breakdown strength. Experimental results show that permittivity increased by factor 7 and electric energy density enhanced by factor 4 as that of pure epoxy at a relatively low filler concentration of 18 wt%. Theoretical modeling of the nanocomposite was done and influence of filler loading on the permittivity, breakdown strength and electric energy density of the nanocomposites were evaluated. From the results, it is seen that theoretical model approximates the experimental values at low filler concentrations.

Rationally designed polyimides for high-energy density capacitor applications.

Development of new dielectric materials is of great importance for a wide range of applications for modern electronics and electrical power systems. The state-of-the-art polymer dielectric is a biaxially oriented polypropylene (BOPP) film having a maximal energy density of 5 J/cm(3) and a high breakdown field of 700 MV/m, but with a limited dielectric constant (∼2.2) and a reduced breakdown strength above 85 °C. Great effort has been put into exploring other materials to fulfill the demand of continuous miniaturization and improved functionality. In this work, a series of polyimides were investigated as potential polymer materials for this application. Polyimide with high dielectric constants of up to 7.8 that exhibits low dissipation factors (<1%) and high energy density around 15 J/cm(3), which is 3 times that of BOPP, was prepared. Our syntheses were guided by high-throughput density functional theory calculations for rational design in terms of a high dielectric constant and band gap. Correlations of experimental and theoretical results through judicious variations of polyimide structures allowed for a clear demonstration of the relationship between chemical functionalities and dielectric properties.

Surface modification of BaTiO3 inclusions in polydicyclopentadiene nanocomposites for energy storage

ABSTRACTA new nanocomposite system displaying high breakdown strength, improved permittivity, low dielectric loss, and high thermal stability is presented. Free‐standing nanocomposite films were prepared via a solvent‐free in‐situ polymerization technique whereby 5 vol % BaTiO3 (BT) nanocrystals with tailored surface chemistry were dispersed in dicyclopentadiene (DCPD) prior to initiation of ring opening metathesis polymerization by a second generation Grubbs catalyst. The relative permittivity was enhanced from 1.7 in the neat poly(DCPD) film to a maximum of 2.4 in the composite, while the dielectric loss tangent was minimized below 0.7%. Surface modification of the BT nanocrystals mitigated reduction in breakdown strength of the resulting nanocomposites such that only a 13% reduction in breakdown strength was observed relative to the neat polymer films. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40290.

Molecular composites with enhanced energy density for electroactive polymers

Actuators based on soft dielectric elastomers deform due to electric field induced Maxwell's stress, interacting with the mechanical properties of the material. The relatively high operating voltages of such actuators can be reduced by increasing the permittivity of the active material, while maintaining the mechanical properties and high electrical breakdown strength. Approaches relying on the use of highly polarizable molecules or conjugated polymers have so far provided the best results, however it has been difficult to maintain high breakdown strengths. In this work, a new approach for increasing the electrostatic energy density of a soft polymer based on molecular composites is presented, relying on chemically grafting soft gel-state π-conjugated conducting macromolecules (polyaniline (PANI)) to a flexible elastomer backbone SEBS-g-MA (poly-styrene-co-ethylene-co-butylene-co-styrene-g-maleic anhydride). The approach was found to result in composites of increased permittivity (470% over the elastomer matrix) with hardly any reduction in breakdown strength (from 140 to 120 V μm−1), resulting in a large increase in stored electrostatic energy. This led to an improvement in the measured electromechanical response as well as in the maximum actuation strain. A transition was observed when amounts of PANI exceeded 2 vol%, which was ascribed to the exhaustion of the MA-functionality of the SEBS-g-MA. The transition led to drastic increases in permittivity and conductivity, and a sharp drop in electrical breakdown strength. Although the transition caused further improvement of the electromechanical response, the reduction in electrical breakdown strength caused a limitation of the maximum achievable actuation strain.

Simulation on the time dependence of breakdown strength in insulating polymers

On the basis of the percolation model for electrical breakdown in insulating polymers, a simulation approach was put forward for the process of electrical aging. The deteriorated regions formed by bond scission are expressed as the sites with lower trap barriers, and the local deterioration rate is related to both the electrical field and the size of existing deteriorated regions. Then the reduction of breakdown strength (or the percolation threshold) with the increase of deteriorated sites can be simulated. Assuming a parameter β to reflect the effect of the size of existing deteriorated region, simulation results show two types of breakdown: percolationlike breakdown for β⩽2 (in which the percolation threshold is reduced due to the gradual global increase of deteriorated sites) and avalanchelike breakdown for β&amp;gt;2 (in which breakdown occurs by the rapid growth of a filamentary structure). Moreover, it is indicated that the lifetime might not be in inverse proportion to the local deterioration rate in the case of percolationlike breakdown.

Inception and propagation mechanisms of water treeing

Mechanisms of water treeing are reviewed. A definition of water trees is proposed on the basis of permanent the hydrophilic character and the reduced breakdown strength. Properties are discussed that are relevant to the water tree definition and to the inception and propagation mechanism. This includes the water content, the (sub)micrometer structure and the dielectric properties. The discussed propagation mechanisms include electro-mechanical forces, diffusion of hydrophilic species and two types of oxidation mechanisms. Also attention is paid to the correlations between processes and aging conditions. Inception mechanisms include injection of hydrophilic species and/or oxidation in damaged regions, electro-mechanical damage due to high electrical fields.

The electrical properties of some cordierite glass ceramics in the system MgO-Al2O3-SiO2-TiO2

The a.c. dielectric breakdown and electrical resistivity of glass ceramics in the system MgO-Al2O3-SiO2-TiO2 have been studied using three sets of samples having different crystallinity contents. Standard a.c. (50 Hz) breakdown tests were performed at room temperature (18 °C) using planar disc specimens and hemispherically-ended brass contact electrodes. The breakdown process caused the formation of a breakdown channel which terminated at the specimen surface in a crater. The breakdown strength was independent of the rate of voltage rise, but decreased exponentially (60 to 10 kV mm−1) with increasing specimen thickness. A high crystallinity content, good surface finish and a homogeneous microstructure yielded high breakdown strengths whilst poor microstructural development caused a reduction in breakdown strength. The breakdown mechanism is believed to be a combination of electronic, thermal and electromechanical processes.

The Effect of X-Rays on the Breakdown Strength and Flashover Voltage of Certain Dielectrics

Qualitative measurements are made on the reduction of breakdown strength of certain solid, liquid, and gaseous insulations. The observed reduction in breakdown strength is influenced by the gap length as well as the quantity of the x-rays. Exposing a solid to air boundary to x-rays increases the flashover voltage. A theory for this effect is offered.