Electrical Dielectric Breakdown Research Articles

Highly Thermally Conductive Aramid Nanofiber Composite Films with Synchronous Visible/Infrared Camouflages and Information Encryption

AbstractThe development of highly thermally conductive composites that combine visible light/infrared camouflage and information encryption has been endowed with great significance in facilitating the application of 5G communication technology in military fields. This work uses aramid nanofibers (ANF) as the matrix, hetero‐structured silver nanowires@boron nitride nanosheets (AgNWs@BNNS) prepared by in situ growth as fillers, which are combined to fabricate sandwich structured thermally conductive and electrically insulating (BNNS/ANF)‐(AgNWs@BNNS)‐(BNNS/ANF) (denoted as BAB) composite films by “filtration self‐assembly, air spraying, and hot‐pressing” method. When the mass ratio of AgNWs@BNNS to BNNS is 1 : 1 and the total mass fraction is 50 wt %, BAB composite film has the maximum in‐plane thermal conductivity coefficient (λ∥ of 10.36 W/(m ⋅ K)), excellent electrical insulation (breakdown strength and volume resistivity of 41.5 kV/mm and 1.21×1015 Ω ⋅ cm, respectively) and mechanical properties (tensile strength of 170.9 MPa). 50 wt % BAB composite film could efficiently reduce the equilibrium temperature of the central processing unit (CPU) working at full power, resulting in 7.0 °C lower than that of the CPU solely integrated with ANF directly. In addition, BAB composite film boasts adaptive visible light/infrared dual camouflage properties on cement roads and jungle environments, as well as the function of fast encryption of QR code information within 24 seconds.

Highly Thermally Conductive Aramid Nanofiber Composite Films with Synchronous Visible/Infrared Camouflages and Information Encryption.

The development of highly thermally conductive composites that combine visible light/infrared camouflage and information encryption has been endowed with great significance in facilitating the application of 5G communication technology in military fields. This work uses aramid nanofibers (ANF) as the matrix, hetero-structured silver nanowires@boron nitride nanosheets (AgNWs@BNNS) prepared by in situ growth as fillers, which are combined to fabricate sandwich structured thermally conductive and electrically insulating (BNNS/ANF)-(AgNWs@BNNS)-(BNNS/ANF) (denoted as BAB) composite films by "filtration self-assembly, air spraying, and hot-pressing" method. When the mass ratio of AgNWs@BNNS to BNNS is 1 : 1 and the total mass fraction is 50 wt %, BAB composite film has the maximum in-plane thermal conductivity coefficient (λ∥ of 10.36 W/(m ⋅ K)), excellent electrical insulation (breakdown strength and volume resistivity of 41.5 kV/mm and 1.21×1015 Ω ⋅ cm, respectively) and mechanical properties (tensile strength of 170.9 MPa). 50 wt % BAB composite film could efficiently reduce the equilibrium temperature of the central processing unit (CPU) working at full power, resulting in 7.0 °C lower than that of the CPU solely integrated with ANF directly. In addition, BAB composite film boasts adaptive visible light/infrared dual camouflage properties on cement roads and jungle environments, as well as the function of fast encryption of QR code information within 24 seconds.

Mathematical model of thermal breakdown of electrical insulation made of polymer composite

Mathematical model of thermal breakdown of electrical insulation made of polymer composite

НАДЁЖНОСТЬ ИЗОЛЯЦИИ СТАТОРНЫХ ОБМОТОК ЧАСТОТНО-УПРАВЛЯЕМЫХ ЭЛЕКТРОДВИГАТЕЛЕЙ

Relevance Widespread use of semiconductor frequency converters is due to the significant advantages of this technology: smoothness and accuracy of controlling the speed and torque of the electric motor, smooth start and stop; increased energy efficiency; the possibility of remote monitoring, etc. The accumulated operational experience has shown an increased failure rate of stator winding insulation of asynchronous motors operating with pulsed power. The presence of high-frequency overvoltages in the inverter signal can lead to the appearance of partial discharges even in the low-voltage motors windings. It’s leading to accelerated degradation of electrical insulation and premature breakdown. Over the past three decades, a significant amount of information has been accumulated in the technical literature: high-frequency transient models have been created; partialdischarge and corona-resistant test methods have been developed; the most important voltage parameters determining the intensity of insulation aging have been determined; regulatory documentation for testing and selection of insulation systems have been developed. Analysis and systematization of existing results are necessary to determine the directions of further research in the subject. Аim of research Identification of new solutions and trends of insulation reliability windings of lowvoltage electric machines when powered by modulated voltage. Research methods Bibliographic analysis, methods of statistical data processing. Results Analysis of the most relevant works on the reliability of low-voltage winding insulation systems in frequency electric drive systems is carried out, a bibliographic list of these works is given. The main results concerning the overvoltages simulation, insulation testing methods, studying the aging mechanisms of winding polymer insulation with pulsed power supply, determining the characteristics of emerging discharges are shown. The ways of further development aimed at modeling overvoltages, taking into account high-frequency effects, increasing the volume of experiments to estimate the insulation lifetime, studying the conditions for the occurrence of partial discharges, creating a common approach to insulation testing are determined.

A Smart Overvoltage Monitoring and Hierarchical Pattern Recognizing System for Power Grid with HTS Cables

As one part of the power system, high-temperature superconducting (HTS) cables may be subject to various system faults, such as overvoltage. When overvoltage occurs, HTS cables may quench and the resistance of HTS tapes will increase rapidly, which will result in reduction of transmission capacity, increase of power loss and even electrical insulation breakdown. To protect the operation safety of power system, the level of overvoltage should be investigated in the system. This paper proposes a non-contact variable frequency sampling and hierarchical pattern recognizing system for overvoltage. Lightning and internal overvoltage signals are captured by specially designed non-contact voltage sensors. The sensors are installed at the grounding tap of transformer bushings and the cross arm of transmission towers. A variable sampling technique is employed to solve the conflict between sampling speed and storage capacity. A hierarchical pattern recognizing system is proposed to subdivide each overvoltage into specific types. Seven common overvoltages are discussed and analyzed. Wavelet theory and S-transform singular value decomposition (SVD) theory are adopted to extract the feature parameters of different overvoltages. Particle swarm optimization is employed to maintain a high classification rate and improve the initial set of the support vector machine (SVM) used as recognition algorithm. Field-acquired overvoltage data from an 110 kV substation validate the effectiveness of the proposed recognition system.

Tensile and Electrical Insulation Properties of Epoxy/Micro-silica Composites

The effect of epoxy species on the tensile and electrical insulation properties of epoxy/micro-silica composites was studied by using three species of epoxy resins for high voltage insulators. The mixing ratio of spherical type micro-silica was varied at 40–70 wt% in each epoxy systems. Tensile strength of three Epoxy/micro-silica composites was lower than that of the each neat epoxy system and increased with increasing micro-silica content in each system. The maximum tensile strength was 86.0 MPa in Epoxy 2/micro-silica (70 wt%) composite. Electrical insulation breakdown strength of three Epoxy 1/micro-silica, Epoxy 2/micro-silica, Epoxy 3/micro-silica composites was higher than that of the each neat Epoxy 1, Epoxy 2 and Epoxy 3. The maximum electrical insulation breakdown strength was 55 kV/2mm in Epoxy 2/micro-silica (50 wt%) composite.

Modelling and simulation of PD characteristics in non-conductive electrical trees

Electric tree growth is a key ageing mechanism leading to breakdown of high voltage electrical insulation. Partial discharges (PDs) are invariably associated with electrical tree inception and propagation. In turn, the physical structure of an electrical tree influences the characteristics of partial discharge activity. Interpretation of PD patterns is therefore central to developing an understanding of the tree propagation process, and also to the use of PD patterns as an asset management tool. Our previous research indicates that the phase resolved PD (PRPD) patterns and pulse sequence analysis (PSA) patterns evolve with tree propagation. A method was proposed to estimate the point-on-wave inception and extinction voltages of PDs in tree channels within each power cycle. It was shown that the evolution of PD patterns is a consequence of changes to PD inception and extinction voltages as a tree develops. This paper provides a deterministic model of partial discharge in tree channels. Simulations of PDs in a straight non-conductive tree channel are based on experimental PD inception, extinction and residual voltages. The quantitative simulations reproduce almost all the characteristics of observed PRPD and PSA patterns. It is concluded that PD events are determined by five key parameters: tree structure, applied voltage, PD inception voltage, PD extinction voltage and PD residual voltage. Key parameters estimated by the method, and the models proposed explain PD activity in non-conductive trees. It is suggested that the PSA and PRPD patterns should be discussed together to fully understand the PD events. This model forms a platform for generating robust information for asset managers using PD measurements from high voltage equipment in service.

Enhanced thermal conductivity and mechanical property of flexible poly (vinylidene fluoride)/boron nitride/graphite nanoplatelets insulation films with high breakdown strength and reliability

Owing to the integration of power electronic devices and the development of flexible devices, demands for high quality thermal conductive composites have substantially increased. Thus highly flexible poly (vinylidene fluoride)/boron nitride (i.e. PVDF/BN-x) composite films were prepared in this work, and a low quantity of graphite nanoplatelets (GNP) was added to simultaneously improve the thermal and mechanical properties of the film (i.e. PVDF/BN-30/GNP-y). The synergistic effect of the two fillers has been discussed, and results show that the thermal conductivity of PVDF/BN-30/GNP-2.5 reaches up to 0.720 Wm−1K−1 compared with 0.634 Wm−1K−1 of PVDF/BN-30. And the tensile strength is also increased from 12.43 MPa to 20.21 MPa, which has been improved by 63%. In addition, the experiment results validate that the films possess high electrical insulation and satisfactory breakdown strength, which proves its applicability to high-voltage environment. Besides, the thermal conductivity of films can be preserved after 300 thermal shocks with extreme temperature changes. This study provides a kind of flexible thermal interface material with excellent comprehensive properties for application in field of power electronics.

Electrical Properties of Epoxy Composites with Micro-sized Fillers

Electric breakdown strength and dielectric properties of epoxy/micro-silica and epoxy/micro-alumina composites were studied in order to develop an insulation material for high voltage application. Electrical insulation breakdown strength test were carried out in sphere-plate electrodes and the data were statistically estimated by Weibull method. Dielectric properties was also tested for the specimen with 300 μm thick and 30 mm diameter. Electrical breakdown strength of epoxy/micro-silica was higher than that of neat epoxy, and that for epoxy/micro-alumina was also higher than that of neat epoxy. And electrical breakdown strength of epoxy/micro-silica composite was higher than that of epoxy/micro-alumina composite. As silica or alumina content increased, dielectric constant and tanδ increased.

Electrically insulating, layer structured SiR/GNPs/BN thermal management materials with enhanced thermal conductivity and breakdown voltage

Layer structured high-performance thermal management materials via integrating the advantages of boron nitride (BN, electrically insulating) and graphene nanoplatelets (GNPs, highly thermally conductive) as fillers were realized by a facile and scalable strategy. Outstanding thermal conductivity (TC) of 8.45 W m−1 K−1, the highest value among reported electrically insulating polymer-based materials, excellent electrical insulation (breakdown voltage∼5.33 kV/mm; volume resistance ∼1012Ωcm) and superior electromagnetic interface shielding performance are achieved at a filler loading of 17.88 vol%. Moreover, the mechanical properties and hardness are also in quite good range. Thus, a promising method is provided for large scale production of superior thermal management materials.

Electrical AC Insulation Breakdown Characteristics of Various Epoxy / Heterogeneous Inorganic Mixed Composite

Electrical AC Insulation Breakdown Characteristics of Various Epoxy / Heterogeneous Inorganic Mixed Composite

Properties of radiation stable insulation composites for fusion magnet

High field superconducting magnets made of Nb3Al will be a suitable candidate for future fusion device which can provide magnetic field over 15T without critical current degradation caused by strain. The higher magnetic field and the larger current will produce a huge electromagnetic force. Therefore, it is necessary to develop high strength cryogenic structural materials and electrical insulation materials with excellent performance. On the other hand, superconducting magnets in fusion devices will experience significant nuclear radiation exposure during service. While typical structural materials like stainless steel and titanium have proven their ability to withstand these conditions, electrical insulation materials used in these coils have not fared as well. In fact, recent investigations have shown that electrical insulation breakdown is a limiting factor in the performance of high field magnets. The insulation materials used in the high field fusion magnets should be characterized by excellent mechanical properties, high radiation resistivity and good thermal conductivity. To meet these objectives, we designed various insulation materials based on epoxy resins and cyanate ester resins and investigated their processing characteristic and mechanical properties before and after irradiation at low temperature. In this paper, the recent progress of the radiation stable insulation composites for high field fusion magnet is presented. The materials have been irradiated by 60Co γ-ray irradiation in air at ambient temperature with a dose rate of 300 Gy/min. The total doses of 1 MGy, 5 MGy and 10 MGy were selected to the test specimens.

표면처리된 나노알루미나가 첨가된 에폭시/멀티-알루미나 콤포지트의 교류절연파괴 특성

The aim of this study is to improve of properties for electrical AC insulation breakdown strength using epoxy/micro-nano alumina composites with adding glycerol diglycidyl ether (GDE:1,3,5g). This paper deals with the effects of GDE addition for epoxy/micro alumina contents (40,50,60wt%)+surface modified nano alumina(1_phr) composites. 14 kinds specimen were prepared with containing epoxy resins, epoxy micro composites and epoxy nano-micro alumina mixture composites. Average particle size of nano and micro alumina used were 30nm and 1~2㎛, respectively. The micro alumina used were alpha phase with Heterogeneous and nano alumina were gamma phase particles of spherical shape. The electrical AC insulation breakdown strength was evaluated by sphere to sphere electrode system and raising velocity 1㎸/s. The AC breakdown strength decreased insulation properties of multi-composites according to increasing micro alumina and GDE addition contents.

Fault Analysis for 110 kV HTS Power Cables

It is very attractive to replace the traditional power cables into high-temperature superconducting (HTS) cables for electricity transmission to metropolitan areas with the advantages of high capacity and low losses. However, these advantages only present when the conductors are kept in certain low temperature range. When a fault occurs, the HTS cable may quench and the resistivity of the conductor will increase rapidly which will result in the reduction of transmission capacity, increase of the power loss and even electrical insulation breakdown. Therefore, it is necessary to investigate the level of over current and overvoltage. In this paper, an accurate model for a 1-km-long 110 kV HTS cable is given and a simple simulation model for HTS cable is built up using EMTP-ATP program. Single-phase short-circuit fault and electrical insulation breakdown fault are considered to investigate the overvoltage and over current level of the HTS cable. The simulation results may provide instructive guide for the protection systems for HTS cables.

에폭시/구상실리카 콤포지트의 전기적 절연파괴 및 인장 강도 특성 연구

In order to develop a high voltage insulation material, spherical silicas with two average particle sizes of 5 and 20 were mixed in different mixing ratios (1:0, 0.7:0.3, 0.5:0.5, 0.3:0.7, 0:1) and their total filling content was fixed at 65 wt%. In order to observe the dispersion of the spherical silicas and the interfacial morphology between silica and epoxy matrix, field emission scanning electron microscope (FE-SEM) was used. The electrical insulation breakdown strength was estimated in sphere-plate electrodes with different insulation thicknesses of 1, 2, and 3 mm. Electrical insulation breakdown strength decreased with increasing mixing ratio of 5/20 and the thickness dependence of the breakdown strength was also observed. The tensile strength of the neat epoxy was 82.8 MPa as average value and its increased with decreasing particles size and that of epoxy/silica (2 ) was 107 MPa, which was 130.8% higher value.

Effects of Reactive Diluents on the Electrical Insulation Breakdown Strength and Mechanical Properties in an Epoxy System

In order to study the effect of reactive diluents on the electrical insulation breakdown strength and mechanical properties of, a polyglycol and an aliphatic epoxy were individually introduced to an epoxy system. Reactive diluents were used in order to decrease the viscosity of the epoxy system; polyglycol acted as a flexibilizer and 1,4-butanediol diglycidyl ether (BDGE) acted as an aliphatic epoxy, which then acted as a chain extender after curing reaction. The ac electrical breakdown strength was estimated in sphere-to-sphere electrodes and the electrical breakdown strength was estimated by Weibull statistical analysis. The scale parameters of the electrical breakdown strengths for the epoxy resin, epoxy-polyglycol, and epoxy-BDGE were 45.0, 46.2, and 45.1 kV/mm, respectively. The flexural and tensile strengths for epoxy-BDGE were lower than those of the epoxy resin and those for epoxy-polyglycol were lower than those of the epoxy resin.

Effect of Mixing Ratio of Spherical Silica on the Electrical Insulation Breakdown Strength in Epoxy Composites

The effect of the mixing ratio of spherical silica on the electrical insulation breakdown strength in an epoxy/silica composite was studied. Spherical silicas with two average particle sizes of and were mixed in different mixing ratios, and their total filling content was fixed at 60 wt%. In order to observe the dispersion of the silicas and the interfacial morphology between silica and epoxy matrix, scanning electron microscopy (SEM) was used. The electrical insulation breakdown strength was estimated in sphere-sphere electrodes with different insulation thicknesses of 1, 2, and 3 mm. Electrical insulation breakdown strength decreased with increasing mixing ratio of and the thickness dependence of the breakdown strength was also observed.

Electrical Insulation Breakdown Strength in Epoxy/Spherical Alumina Composites for HV Insulation

In order to develop high voltage (HV) insulation materials, epoxy/spherical alumina composites with two different particle sizes (in <TEX>${\mu}m$</TEX>) were prepared and a dynamic mechanical analysis (DMA) and electrical insulation breakdown strength test were carried out in sphere-sphere electrodes and the data were estimated using Weibull statistical analysis. Alumina content varied from 50 to 70 wt%. The electrical insulation breakdown strength for epoxy/alumina (50 wt%) was 44.0 kV/1 mm and this value decreased with increasing alumina content. The effects of insulation thickness and alumina particle size on the insulation breakdown strength were also studied. The insulation thickness varied from 1 mm to 3 mm, and the particle sizes were 7.3 or <TEX>$40.3{\mu}m$</TEX>.

Effect of Particle Size on the Mechanical and Electrical Properties of Epoxy/Spherical Silica Composites

The effects of particle size on the mechanical and electrical properties of epoxy/spherical silica composites were studied. The silica particle sizes were varied from 5 to 30 <TEX>${\mu}m$</TEX> and the filler content was fixed to 60 wt%. Tensile and flexural tests were carried out and the interfacial morphology was observed by scanning electron microscopy (SEM). The electrical insulation breakdown strength was estimated using sphere-sphere electrodes with different insulation thicknesses of 1, 2 and 3 mm. The tensile strength and flexural strength increased with decreasing particle size, while electrical insulation breakdown strength increased with increasing particle size.

Long-term and Short-term AC Treeing Breakdown of Epoxy/Micro-Silica/Nano-Silicate Composite in Needle-Plate Electrodes

In order to characterize insulation properties of epoxy/micro-silica/nano-silicate composite (EMNC), long-term and short-term AC treeing tests were carried out undr non-uniform electric field generated between needle-plate electrodes. In a long-term test, a 10 kV (60 Hz) electrical field was applied to the specimen positioned between the electrodes with a distance of 2.7 mm in an insulating oil bath at <TEX>$30^{\circ}C$</TEX>, and a typical branch type electrical tree was observed in the neat epoxy resin and breakdown took place at 1,042 min after applying the 10 kVelectrical field. Meanwhile, the spherical tree with the tree length of <TEX>$237{\mu}m$</TEX> was seen in EMNC-65-0.3 at 52,380 min (36.4 day) and then the test was stopped because the tree propagation rate was too low. In the short-term test, an electrial field was applied to a 3.5 mm-thick specimen at an increasing voltage rate of 0.5 kV/s until breakdown in insulating oil bath at <TEX>$30^{\circ}C$</TEX> and <TEX>$130^{\circ}C$</TEX>, and the data was estimated by Weibull statistical analysis. The electrical insulation breakdown strength for neat epoxy resin was 1,763 kV/mm at <TEX>$30^{\circ}C$</TEX>, while that for EMNC-65-0.3 was 2,604 kV/mm, which was a modified value of 47%. As was expected, the breakdown strength decreased at higher test temperatures.