Decrease In Breakdown Strength Research Articles

Erosion behaviors and mechanisms of Ti3AlC2 material under arc discharge in various mixed atmospheres

The present study establishes an experimental platform for investigating arc erosion and explores the erosion characteristics of Ti3AlC2 material under a voltage of 10 kV in SF6/N2, SF6/CO2, and N2/CO2 environments. Our findings reveal that the arc energy and duration exhibit a gradual increase in the sequence of SF6/N2, SF6/CO2, and N2/CO2, while the breakdown strength decreases. Scanning electron microscopy (SEM) and a three-dimensional laser confocal microscope were employed to observe uneven erosion morphology. Additionally, high-speed camera footage captures the arc bending and drifting phenomenon caused by Rayleigh-Taylor instability between the arc and gas. X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) analysis were utilized to characterize the composition of eroded surfaces. Erosion models were proposed for each mixed atmosphere along with comprehensive discussions on their underlying mechanisms. This work expands the application scope of MAX phase materials while providing a theoretical foundation for designing electrical contact materials.

High temperature electrical breakdown and energy storage performance improved by hindering molecular motion in polyetherimide nanocomposites

Polyetherimide (PEI) is widely used as a material for high temperature and high power energy storage capacitors in new energy vehicles and other fields. However, as the temperature increases, the electrical conductivity increases and the breakdown strength decreases, which greatly reduces the energy storage density of the capacitor and limits the application range. In order to clarify the influence mechanism of high temperature on the breakdown and energy storage performance of dielectrics, this paper established a charge capture and molecular displacement (CTMD) breakdown model based on the expansion motion of molecular segments to study the charge transport and molecular chain motion process of PEI nanocomposites (PNCs) at high temperature. The results show that at 100 °C, compared with pure PEI, the internal maximum molecular displacement of PEI PNCs with appropriate doping content (3 wt%) is reduced by 28.79 %, and the breakdown strength is increased by 11.20 %. Appropriate nano-doping can effectively increase the movement difficulty of molecular chains and reduce the activation volume that provides energy for charge transport. Thus, charge transport is inhibited, current density is reduced, and Joule heat accumulation is avoided. Finally, the high temperature breakdown and energy storage performance are improved.

Effect of sintering temperature on dielectric and electrical properties of bio-waste derived beta-dicalcium silicate

Beta-dicalcium silicate ceramics were synthesized by mechanochemical-assisted solid-state reaction route using rice husks and chicken eggshells as silica and calcium oxide sources. The ceramics were sintered at 900, 1000, and 1100 °C for 2 h in air. The effect of sintering temperature on these ceramics' morphological, breakdown strength, dielectric, and electrical properties was investigated. It was found that the ceramic sintered at the optimized temperature of 1100 °C formed the pure β-dicalcium silicate (β-Ca2SiO4). Scanning electron micrographs showed that with the increase in sintering temperature, the average grain size and pore size of the sintered ceramics increased while the grain boundary density decreased, which promoted the breakdown path and resulted in a decrease in breakdown strength. The dielectric behavior examined from 25 to 300 °C and in a frequency range of 4–5 MHz found that the dielectric constant and loss tangent decreased with increasing frequency. Nyquist plot of impedance confirmed a non-Debye type relaxation, and grain and grain boundary contributions were revealed from equivalent circuit fitting. Variations of impedance spectroscopy reflect the positive and negative temperature coefficient of resistance behavior for these ceramics. Electric modulus spectra revealed that with the sintering temperature increase, the samples' conductivity activation energies increased from 0.35 to 0.46 eV. All the sintered samples attained low dielectric loss (0.004 < tanδ < 0.1) above 103 Hz, which makes them suitable materials for capacitor application.

Epoxy-based high-k composite vitrimer: With low dielectric loss, high breakdown strength and surface electrical damage repairability

High dielectric constant/permittivity (high-k) polymer-matrix composites (PMCs) are widely used in the electronics and electrical industries since their high energy density, ease of processing and light weight. However, the high dielectric permittivity (εr) usually leads to a significant increase in dielectric loss (tanδ) and an obvious decrease in breakdown strength (Eb), which is still a major problem that restricts the development of high-k PMCs. In addition, to extend the service life, the next generation electrical/electronic components also demand materials have electrical damage repairability. In this study, a new epoxy-based high-k composite vitrimer was constructed. The dynamic disulfide bonds were introduced into the cross-linked network to provide the high-k composite vitrimer with excellent repairability, while the nanoparticle (NPs) fillers surfaces were modified by grafting disulfides to improve the dynamic rearrangement ability of the composite network and enhance the electrical properties of the high-k composite vitrimer. The results show that this high-k composite vitrimer has low tanδ and high Eb, which is about 0.025 (at 0.1 Hz and room temperature) and 26.0 kV/mm (under 50 Hz AC voltage of 1 mm samples), respectively. Moreover, it has excellent mechanical damages and electrical damages repairability. For mechanical damages, it can repair mechanical scratches by heating at 180 °C for 10 min. For surface electrical damages, it can also eliminate the residual carbons, regain the surface organic structure, and restore more than 94% insulation strength by thoil treatment under 80 °C for 60 min. This study provides a new reference method for the preparation of low tanδ, high Eb and repairable high-k PMCs.

Anomalous Residual Stress Behavior and Corresponding Dielectric Properties of Epoxy Resin Induced by Physical Aging

In this paper, we report an anomalous behavior of residual stress in epoxy resin insulation, which decreased with elevated cooling rate from an initial temperature below the glass transition temperature ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> ). It was found that an increased cooling rate from 9 K/h to 120 K/h led to a decreased residual stress by 37%. Further results of dielectric relaxation and volumetric strain suggest the physical aging as the origin of this anomalous residual stress behavior, which resulted in enhanced chain relaxation on the micro level and volumetric shrinkage on the macro level. It is suggested that the larger residual stress is caused by both greater interaction between chains and larger volumetric shrinkage in the specimens with lower cooling rate. In addition, shortened cooling time also induced insufficient chain curling and thus increased free volume, which can be further supported by enhanced charge mobility and lowered DC breakdown strength. A 13% decrease in breakdown strength and a 38% increase in the charge mobility were found provided the cooling rate enhanced from 9 K/h to 120 K/h. This work proposed a new comprehending into the residual stress from curing cooling process and corresponding dielectric properties of epoxy resin insulation.

Arc Erosion Properties of WCu Material Reinforced with Ti3SiC2under Different Applied Voltages

Introducing reinforcements is a crucial way to modify WCu electric contacts. Herein, the arc erosion performances of WCu/Ti3SiC2under various direct current voltages are investigated. The eroded microstructures are observed by a 3D laser scanning confocal microscopy and a thermal field emission scanning electron microscope. Compositions of the eroded surfaces are analyzed by a Raman spectroscopy. With the elevated voltages, values of breakdown current, arc duration, arc energy, and arc discharge distance increase, while the breakdown strength decreases. Meanwhile, the eroded regions gradually change from circular shape to irregularly curved corrugations under the elevated voltages. Copper and Ti3SiC2can disperse arc during arc discharge, and the liquid and gas generated by the two phases can make differences in protecting WCu/Ti3SiC2.

Exploration of Breakdown Strength Decrease and Mitigation of Ultrathin Polypropylene.

Polypropylene film is the most important organic dielectric in capacitor technology; however, applications such as power electronic devices require more miniaturized capacitors and thinner dielectric films. The commercial biaxially oriented polypropylene film is losing the advantage of its high breakdown strength as it becomes thinner. This work carefully studies the breakdown strength of the film between 1 and 5 microns. The breakdown strength drops rapidly and hardly ensures that the capacitor reaches a volumetric energy density of 2 J/cm3. Differential scanning calorimetry, X-ray, and SEM analyses showed that this phenomenon has nothing to do with the crystallographic orientation and crystallinity of the film but is closely related to the non-uniform fibers and many voids produced by overstretching the film. Measures must be taken to avoid their premature breakdown due to high local electric fields. An improvement below 5 microns will maintain a high energy density and the important application of polypropylene films in capacitors. Without destroying the physical properties of commercial films, this work employs the ALD oxide coating scheme to augment the dielectric strength of a BOPP in the thickness range below 5 μm, especially its high temperature performance. Therefore, the problem of the reduction in dielectric strength and energy density caused by BOPP thinning can be alleviated.

Degradation Behavior and Mechanism of Metalized Film Capacitor Under Ultrahigh Field

Metalized film capacitor degradation under ultrahigh electric fields is crucial for the reliability of voltage source converter (VSC)-HVDC systems. In the present study, systematic investigations were performed that metalized film capacitors were aged under the dc electric field ranging from 300 to 400 kV/mm. Results showed that under moderate electric field, the capacitance reduction of sample capacitors presented two stages with different decay rates. With the increase of the electric field, the rapid degradation occurred immediately on the starting of the aging process, suggesting a voltage threshold determining the capacitors’ stability. In addition, the degradation mechanisms of both metalized films and biaxial oriented polypropylene (BOPP) base films were investigated by statistical analysis and structural experiments. Below the voltage threshold, more shallow traps were generated and the activation energy of molecular motions was reduced due to PP molecules scissions, resulting in the decrease of breakdown strength (BDS) of BOPP films. While above the voltage threshold, the accelerated failure could be attributed to two main causes: the fast breakdown of originally formed weak points and the dramatically increased self-healing area. The study can contribute to the design and evaluation of dc-link capacitors both experimentally and theoretically.

Novel multifunctional melamine borate - boron nitride nanosheets/epoxy composites with enhanced thermal conductivity, flame retardancy and satisfying electrical insulation

In this work, we present a solution to use nitrogen and boron co-effect flame-retardant (melamine borate, abbreviated as MB) functionalized boron nitride nanosheets (MB-BNNS) to improve the thermal conductivity and flame retardance of epoxy resin and maintain excellent electrically insulating properties simultaneously. In brief, the MB-BNNS were prepared by grafting MB onto boron nitride surfaces via a simple ball-milling and eco-friendly water scrubbing process. Subsequently, the epoxy composites with uniformly dispersed MB-BNNS were obtained by wet processing. The obtained epoxy composite with 5 vol% EP/MB-BNNS showed a optimally comprehensive performance. Compared to pure epoxy, it showed 108% of increase in thermal conductivity (TC), 36.44% and 32.06% of decrease in peak heat release rate (PHRR) and total heat release rate (THR), and slightly decrease in dielectric breakdown strength. More remarkably, the release percentages of toxic and combustible gases in EP/MB-BNNS composite system were significantly reduced, which were measured by a in-situ measurement.

Curing Kinetics and Dielectric Properties of Anhydride Cured Epoxy Resin With Different Accelerator Contents

The addition of accelerator reduces the curing reaction temperature, changes the curing reaction process, and affects the morphology of the crosslinking structure, which would lead to the difference in the dielectric properties of the epoxy resin. In this study, the curing behaviors and dielectric properties of diglycidyl ether of bisphenol A (DGEBA)/methyl hexahydrophthalic anhydride (MHHPA) were investigated with respect to the contents of the curing accelerator, Tris-(dimethylaminomethyl) phenol (DMP-30). The curing behavior of epoxy resin was studied by differential scanning calorimetry (DSC), and it was found that the system conforms to the Sestak–Berggren kinetic model [SB ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${m},{n}{)}$ </tex-math></inline-formula> ]. The accelerator content has a saturation effect on the dielectric properties of the epoxy resin curing sample, and excessive content can lead to the increase of dielectric constant and loss and decrease of breakdown strength. The cured sample with 0.5% accelerator addition has the best dielectric properties and the highest breakdown strength. The analysis concludes that the optimum accelerator content allows for a more rational curing crosslinking network.

A Method to Characterize the Shrinking of Safe Operation Area of Metallized Film Capacitor Considering Electrothermal Coupling and Aging in Power Electronics Applications

Metallized film capacitor (MFC) selection is a key step to ensure the safe and reliable operation of high-capacity power electronic equipment. However, as a crucial factor leading to overstress failure, the changing of stress tolerance boundary caused by parameter drift and insulation deterioration has not been fully considered in capacitor design. Therefore, the establishment method of MFC lifecycle safe operation area (SOA) is proposed innovatively in this article, which characterize the shrinking of safe operating boundaries caused by electrothermal coupling and capacitor aging during long-term operation. First, the failure mechanisms and electrothermal coupling of MFC are discussed and the modeling process of initial SOA is proposed based on the datasheet and dc withstand voltage experiments. In addition, considering the increase of the hot-spot temperature and the decrease of breakdown strength due to equivalent series resistance parameter drift and dielectric insulation degradation in the whole lifecycle, the shrinking of MFC operation boundary is characterized and the modeling process of lifecycle SOA is proposed based on aging model and lifetime tests. Finally, taking an MMC system as example, the MFC selection based on practical operating condition and lifecycle SOA is performed to verify the validity of the method.

Ferromagnetic Quantum Dots Improving Polypropylene Film Performance in Strong Electromagnetic Field

In this article, the performance degradation of polypropylene (PP) films is investigated in a 0–12-T magnetic field. A modification method is proposed based on ferromagnetic quantum dots (QDs) blending. The experimental results show that the 12-T magnetic field reduces the relative permittivity by 0.07 at 1 kHz. The conductivity of PP films increases by 230% and the breakdown strength decreases by 16.8% under 12 T. After blending 20-nm Fe3O4 particles, the conductivity of the composite films is reduced by 70% under 0 T and 64.6% under 12 T. The withstand voltage increases by 13% under 0 T and 24% under 12 T. The energy density of the 0.2 wt% blending composite films increases from 2.07 to 3.12 J/cm3 under 12 T. Further analysis shows that the magnetic field leads to the film performance degradation by restraining polarization and exciting electrons. Doping Fe3O4 nanoparticles can slightly enhance polarization with the introduction of the interface and capture electrons to improve the electric resistance and the breakdown strength. This article is of significance to the performance optimization of PP dielectric for power capacitors in an electromagnetic environment.

Effect of Aged Nonlinear Resistive Field Grading Material on Electric Field Distribution of DC Cone Spacer

Nonlinear resistive field grading materials are widely used in the electrical and electronic applications, and are usually researched based on the initial nonlinear conductivity characteristics of synthetic materials. However, the long-term stability of these materials are rarely reported. In this paper, the effects of thermal ageing on nonlinear resistive field grading material and the electric field distribution of DC cone spacers are studied. The 30 wt.% SiC/epoxy micro-composites are prepared and are thermally aged at 180 °C for 1080 h. The infrared spectroscopy, dielectric properties, breakdown strength and nonlinear conductivity are measured, respectively. In addition, a simulation model for a cone spacer is built, and the electric field and power dissipation density are calculated. With the increasing thermal ageing time, the relative permittivity and loss tangent increase, and the breakdown strength decreases. Besides, the nonlinear coefficient of nonlinear conductivity almost increases, and the switching electric field of nonlinear conductivity decreases. Simulation results show that the aged micro-composites can homogenize the electric field in the cone spacer, but the thermal ageing causes the increase in power dissipation density and threatens the safe operation of the cone spacer.

High energy density nanocomposites with layered gradient structure and lysozyme-modified Ba0.6Sr0.4TiO3 nanoparticles

Polymer nanocomposites with high-dielectric-constant ceramic fillers have been supposed to a positive candidate for electrostatic capacitors owing to their higher energy density. Herein, the P(VDF-HFP)/BST (poly(vinylidene fluoride-hexafluoropropylene)/Ba0.6Sr0.4TiO3) nanocomposites films were carefully prepared by layer-by-layer electrospinning, hot-pressing, and quenching processes. In an effort to overcome this challenge that the decrease in breakdown strength due to the high load of ceramic nanoparticles, self-assembly phase-transitioned lysozyme (PTL) is utilized to modify BST (mBST) to improve interface conditions and layered gradient structure is designed to reduce charge injection at the electrode/films respectively. Studying its microstructure and electrical properties found the gradient structure can simultaneously weaken interface defects and improve energy storage performance. Consequently, a remarkable energy density (13.1 J/cm3@450 MV/m) has been obtained compared to that of pure polymer films (5.7 J/cm3). This work presents an attractive approach to enhancing the energy storage properties of polymer nanocomposites by surface modification and structure modulation.

Dielectric Properties of Polymer Films in Strong Electromagnetic Field for Energy Storage Capacitor

In this article, polypropylene (PP), polyimide (PI), polyvinylidene difluoride (PVDF), and polyethylene (PE) dielectric materials are applied to analyze the performance degradation mechanism under magnetic field. The properties of the dielectrics are investigated under different magnetic fields. With the increase of magnetic field, the dielectric constant of materials is reduced and that of PVDF decreases the most. The conductivity of dielectric materials is all on the rise due to the magnetic field. Compared with under normal environment, the conductivity of the PVDF under 12-T magnetic field climbs to 574%, which is the largest increase in all dielectrics. The breakdown strength of PP and PE decreases by 17.2% and that of PVDF decreases by 22%. On the one hand, the magnetic field deflects the electric dipole in the opposite direction through Lorentz force, so as to limit the dipole steering and reduce the dielectric constant. On the other hand, the magnetic field increases the quantity of carriers by exciting electrons, which is the main reason for the decrease of breakdown strength. This article is of significance to the application of dielectric capacitors under harsh magnetic environment.

Investigation on arc erosion characteristics of Ag/Ti3SiC2 composites in SF6 mixed with buffer gases

Electrical contact materials are core components in the gas sealing devices. In an airtight chamber, the arc erosion behaviors of Ag/Ti3SiC2 composites in SF6/N2 and SF6/CO2 were studied. The sample surfaces were observed by TFESEM and 3D LSCM, the phase constituents of the eroded surfaces were revealed by XPS, and the arc discharge frames in SF6 mixtures were observed by a high-speed video camera. With the growing of buffer gases in SF6 mixtures, the breakdown strength decrease, while the erosion area and the arc energy increase. In the two types of SF6 mixtures, the erosion centers are rough and cracks appear on the erosion edges. Seriously in SF6/CO2, oxides and dense pores exist in the erosion regions of Ag/Ti3SiC2 composites. Based on the experimental results, the arc erosion mechanisms of Ag/Ti3SiC2 in SF6 mixtures are proposed.

High-voltage insulation and dielectric properties of ceramic-glass composites

ABSTRACT This paper reveals the high-voltage insulation properties – namely the dielectric constant, dissipation factor, breakdown strength, and voltage – of epoxy resin samples of various thicknesses containing the microadditives albite, potassium feldspar, lithium glass, and zinc glass in different concentrations. 0.1 wt% KAlSi3O8 ceramic powders as fillers in 1 mm epoxy composites designed for insulation is taken as the choice for highest breakdown strength 36.6491 kV/mm. After that, 5 wt% Li-Bi-B-O glass at 35.4687 kV/mm, 10 wt% Zn-Bi-B-O glass at 35.0432 kV/mm, and 10 wt% NaAlSi3O8 at 33.6504 kV/mm. The increase of thickness more than 1 mm is not recommended in the practical application due to the decrease of breakdown strength. Multi-layer thin structure is recommended for insulation purpose.

Breakdown Characteristic Research on Propylene Carbonate After Nano-Modification

Propylene carbonate (PC) has the advantages of great permittivity, high breakdown strength, and great environmental adaptability. However, the applications of propylene carbonate in pulsed power systems have been restricted by the significant polarity effect (differences between the positive breakdown strength and the negative breakdown strength). In this article, the breakdown characteristics of PC by nano-modification under microsecond pulse have been systematically studied. The results showed that the positive breakdown strength is about twice that of the negative breakdown strength of pure PC. After nano-modification, the negative breakdown strength increases significantly, while the positive breakdown strength decreases. The energy band theory of nanofluids was established.

Effects of High Magnetic Field on Partial Discharge and Dielectric Breakdown Behavior of Silicone Rubber

In this article, space charge and partial discharge (PD) behavior and the breakdown strength of silicone rubber under ac and dc voltages are tested in high magnetic field. In the case of ac voltage, the effects of high magnetic field on promoting air gap breakdown result in the decrease in PD inception voltage. Polarization of specimens with higher speed and lower air gap breakdown voltage result in the increase in PD frequency and eventually causes the decrease in breakdown strength. In the case of dc voltage, energy level splitting due to Zeeman effects results in lower interface barrier, considering both the increase in electron affinity and the increase in density deference between donor-like and acceptor-like surface traps. The decrease in interface barrier causes more space charge injection. The electric field distortion caused by local space charge accumulation leads to the decrease in breakdown strength in high magnetic field.

Study on the Influence of Organic–Inorganic Interface Properties on Breakdown Strength and Thermal Properties of MgO/PLA Composites

Polylactic acid (PLA) is expected to be widely used in green power equipment manufacturing due to its good mechanical properties and biodegradability. In this paper, the effects of MgO with different particle sizes and mass fractions on the thermal and electrical properties of PLA composites were studied. The experiment found that with the increase in MgO particle sizes and mass fractions, the thermal conductivity of MgO/PLA composites showed a rising trend, which was up to 165.4% higher than that of pure PLA. However, the heat resistance first increases and then decreases. For the electrical properties of MgO/PLA composites, the breakdown strength and volume resistivity decrease with an increase in MgO particle size and mass fraction. In order to further study the influence mechanism of the introduction of MgO with different particle sizes and mass fractions on the thermal and electrical properties of MgO/PLA composites, molecular dynamics simulation was used to simulate the glass transition temperature (Tg) of PLA composites doped with MgO of different particle sizes, and it was found that MgO doping weakened the movement of the PLA molecular chain segment. Using density functional theory (DFT) calculations, it was found that in the MgO and PLA system, electrons have a tendency to migrate from the PLA matrix to MgO, which causes the formation of electron traps at the inorganic–organic interface and affects its electrical properties. The purpose of this study is to provide a theoretical reference for PLA composites in the manufacture of power equipment.