Electrical Breakdown Phenomena Research Articles

Suppression of electrical breakdown phenomena in liquid TriMethyl Bismuth based ionization detectors

Organometallic liquids provide good properties for ionization detectors. TriMethyl Bismuth (TMBi) has been proposed as a detector medium with charge and Cherenkov photon readout for Positron Emission Tomography. In this work, we present studies for the handling of TMBi at different electric fields and under different environmental conditions to find applicable configurations for the suppression of electrical breakdowns in TMBi at room temperature. A simple glass cell with two electrodes filled with TMBi was constructed and tested under different operation conditions. Working at the vapour pressure of TMBi at room temperature of about 40 mbar and electric fields of up to20 kV/cmin presence of a small oxygen contamination we found the formation of a discharge channel in the liquid and a steady increase in the current. Further reduction of pressure by pumping caused the TMBi to boil and a spontaneous combustion. Eliminating the oxygen contamination led the TMBi under the same condition to only decompose. When operating the setup under an argon atmosphere of 1 bar we did not observe breakdowns of the electrical potential up to field strengths of 20 kV/cm. Still, in presence of a small oxygen contamination fluctuating currents in the nA range were observed, but no decomposition or combustion. We conclude from our experiments that TMBi at room temperature in a pure argon atmosphere of 1 bar remains stable against electrical breakdown at least up to electric field strengths of 20 kV/cm, presumably because the formation of gaseous TMBi was prevented.

Theory of Electrical Breakdown in a Nanocomposite Capacitor

The electrostatic field in a nanocomposite represented by spherical nanoparticles (NPs) embedded into a dielectric between two parallel metallic electrodes is derived from first principles. The NPs are modeled by point dipoles which possess the polarizability of a sphere, and their image potential in the electrodes is found using a dyadic Green’s function. The derived field is used to obtain the parameters which characterize the electrical breakdown in a nanocomposite capacitor. It is found, in particular, that for relatively low volume fractions of NPs, the breakdown voltage linearly decreases with the volume fraction, and the slope of this dependence is explicitly found in terms of the dielectric permittivities of the NPs and the dielectric host. The corresponding decrease in the maximum energy density accumulated in the capacitor is also determined. A comparison with the experimental data on the breakdown strength in polymer films doped with BaTiO3 NPs available in the literature reveals a dominant role of the interface polarization at the NP-polymer interface and an existence of a nonferroelectric surface layer in NPs. This research provides a rigorous approach to the electrical breakdown phenomenon and can be used for a proper design of nanocomposite capacitors.

Effects of Temperature Gradient on Electrical Tree Initiation and Breakdown Phenomenon in XLPE Under Harmonic Superimposed DC Voltage

In this article, the temperature of the needle tip and the ground electrode were changed to obtain different temperature gradients. The harmonic superimposed DC voltage was also simultaneously applied to study the electrical tree initiation, growth and breakdown characteristics in cross-linked polyethylene (XLPE) under the temperature gradient. The tree inception voltage, tree structure, tree length, accumulated damage (AD) and breakdown time were used to analyze the electrical tree degradation process. It was found that the greater the temperature gradient, the easier it is for electrical trees to be initialed which is related to the different charge behaviors affected by the trap distribution indicated by surface potential decay (SPD) results at different temperatures. With the temperature gradient increasing, the electrical tree length increases firstly but then decreases slightly when the temperature of the ground electrode is fixed, but the electrical tree length and AD increase linearly with the temperature gradient increasing when the temperature of the needle tip is fixed. The temperature rise of the ground electrode has a more serious impact on the safety of the insulation compared with the temperature rise of the needle tip. Positive DC bias voltage is more likely to cause damage and breakdown than negative DC bias voltage under the temperature gradient. These results indicate that the temperature gradient and harmonic superimposed DC voltage will promote the electrical growth in cable insulation, so special attention should be paid to the safety of electrical equipment under such special conditions.

Mechanism of flash sintering with high electric field: In the view of electric discharge and breakdown

‘Thermal runaway’ was the most popular mechanism in flash sintering, but this theory was inappropriate under high electric field. In this paper, we described electric discharge and breakdown phenomena in experiment to verify this point. And water moisture was found an important role in conducting electric discharge, that increasing moisture content of samples decreased the onset electric field of flash sintering and as low as 1628 V/cm of onset electric field was realized in this paper. With high electric field that can induce electric discharge in the sample, the flash sintering can be induced at room temperature and atmosphere.

A study of the effect of temperature on the dielectric breakdown and lifetime of polyethylene materials under applied DC voltages at the nanoscale

The reported simulation results could be considered as one of the firsts modeling of the effect of temperature on the electrical breakdown phenomenon in polyethylene nanoscale. The breakdown begins with an abrupt increase of the external current density without a subsequent saturation. Our results show that the increase of temperature at a constant applied DC voltage leads to a breakdown and to a decrease of the insulator's lifetime. These outcomes are strongly linked to the injection of free charges into the sample and to the temporal evolution of the conduction current.

Математична модель ініціювання розрядного процесу у рідких органічних відходах

In connection with the rapid development of high-voltage pulse technology, the phenomenon of electrical breakdown in a liquid is of increasing interest. Depending on the purpose of the installation, the working chamber can have various sizes and shapes. To process the waste of pig-breeding complexes, we have developed an electropulse installation, the working chamber of which has a cylindrical shape, which allows us to simplify the modeling of processes that will occur during the breakdown of liquid in the chamber. The nature and sequence of the discharge processes of the installation depends on such parameters as the state of the electrodes, their shape of exacerbation, the length of the interelectrode gap, the viscosity of the liquid in the chamber, and the presence of impurities. The use of a high-voltage spark as a “working tool” became the first stage of a complex technological process in which a liquid-insulating working medium. The article gives a generalized scheme of the experimental setup, the questions of mathematical modeling of the optimal operating modes of the electric pulse installation are considered. The features of constructing a mathematical model of the electropulse conversion of energy in liquid are considered. Considerable attention is paid to the process of operation of an electric pulse installation, where the current technological mechanism is pressure pulses that emit in the channel of high voltage discharges in an organic liquid. The effectiveness of the impact of pulses is spatially limited and decreases sharply with increasing distance from the axis of the channel and therefore it must be adjusted during the processing of the liquid. In the calculation mathematical model it is necessary to take into account factors affecting the parameters of the pressure pulse in the liquid and the position of the electrodes in space. The article presents the equations of a linearized mathematical model of the processes that occur in the discharge channel of the working body of the electric pulse installation. Key words: mathematical model, electric pulse installation, liquid organic waste

Autonomous Self-Healing of Electrical Degradation in Dielectric Polymers Using In Situ Electroluminescence

Summary Dielectric polymers are ubiquitous as electrical insulation in electrical power systems and electronic devices. Electrical treeing is typically regarded as an irreversible degradation process of dielectric polymers subjected to high electric stresses, which significantly limits their lifespan and endangers the reliability of electronics and electrical power systems. Here, we report self-healing polymers consisting of microcapsules that are capable of completely restoring the dielectric properties as a direct response to electrical tree degradation. We design the microcapsules with a relatively higher dielectric constant than polymer matrix to guide the propagation of electrical trees. The electroluminescence generated in situ during electrical treeing of polymers triggers crosslinking of the healing agents released from the capsules to repair the electrically damaged areas under ambient conditions. Notably, the breakdown strength of the mended region is largely enhanced upon healing, which was initiated at different locations. The integration of autonomous healing capability into dielectric materials opens new avenues to smart polymers for electronics and energy applications.

Declined Fatigue Crack Propagation Rate of a High‐Strength Steel by Electropulsing Treatment

The fatigue crack propagation behavior is a key issue for the service of engineering materials. The effect of electropulsing treatment (EPT) on the growth of fatigue crack in a high‐strength steel (AISI 4340 steel) is investigated. It is shown that the crack propagation rate could be significantly declined via high‐density EPT. The crack features of fracture surface are examined using laser scanning confocal microscopy (LSCM) and scanning electron microscopy (SEM). The crack deviation, local crack‐healing and bridging phenomenon are proposed to be beneficial to lower the crack propagation rate, which should be brought out by the current detour, selective Joule heating, compressive stress, and electrical breakdown phenomenon. All these EPT effects exhibit significant contributions to the improvement of fatigue properties in the widely used high‐strength steel.

Experimental study on the reliability of water/fluoropolymer/ITO contact in electrowetting displays

Abstract The practicability of using DI water in electrowetting displays with a thick layer of fluoropolymer and the reliability of water/fluoropolymer/indium tin oxide contact was investigated experimentally. Electrowetting performances of DI water on a fluoropolymer coating of indium tin oxide surface were tested via sessile droplet test, compared with that of ionic solutions. A platform with a camera system was built to study the electrical property and breakdown phenomenon in water/fluoropolymer/indium tin oxide contact under a DC voltage sweep up to 200 V. The I-V characteristics and synchronized video were used to analyze the charge transport mechanism and anodic/cathodic reactions in the failure process. DI water was proved to be conducting enough for electrowetting displays and liquid conductivity had very little influence on the electrowetting performance. The failure processes of samples with fluoropolymer coating of different thicknesses were studied. Samples with relatively thin fluoropolymer coating showed a rapid increasing leakage current after certain voltage threshold and severe gas evolution, ITO corrosion and fluoropolymer delamination were observed via the camera system. Samples with fluoropolymer coating thicker than 800 nm showed good insulating property in the I-V test and only a few gas bubbles and pitting corrosion dots were observed. The sample with a fluoropolymer coating of 1000 nm showed a maximum leakage current density of 13.6 µA/cm2 at the voltage of 200 V, which is promising for a single layer electrowetting display device.

Electrical treeing initiation and breakdown phenomenon in polypropylene under DC and pulse combined voltages

In this paper, the effects of DC voltage, pulse voltage and pulse frequency on the electrical treeing characteristics in polypropylene (PP) under DC and pulse combined voltages were investigated. The rise time of the pulse voltage is 50 μs. The DC amplitude range is from −25 kV to +25 kV, and the pulse amplitude range is from −35 kV to +35 kV. The pulse frequency range is from 400 to 800 Hz. The results show that the electrical tree structures change with different DC amplitudes, pulse amplitudes and pulse frequencies. With the increase in the positive DC voltage, the treeing process is accelerated. However, with the increase in the negative DC amplitude, the breakdown time decreases first and then increases. This phenomenon is attributed to the different charge transport processes under different DC amplitudes. With the pulse amplitude and frequency increasing, the growth rate and accumulated damage increase significantly. The pulse amplitude and frequency affect significantly the breakdown time. The pulse voltage with the same polarity as that of the DC voltage is more likely to cause breakdown than the pulse voltage with opposite polarity of that of the DC voltage because of the larger effective values of the composite voltages.

Polarity Effect and Dielectric Breakdown of Composite Ferroelectric Films as the Dielectric for Electrowetting Systems

In this paper, we study the electrical properties and breakdown phenomena of BaTiO3/Teflon composite ferroelectric thin film in electrowetting systems. The experimental results showed that the electrowetting effect and the breakdown voltage depend on DC voltage polarity, and this polarity dependence is closely related to the thickness of the ferroelectric film. Under AC voltages, the breakdown voltage increased directly with voltage frequency. These results are useful for designing reliable EWOD devices with low operation voltages and high robustness.

Two-Dimensional Thickness-Dependent Avalanche Breakdown Phenomena in MoS2 Field-Effect Transistors under High Electric Fields.

As two-dimensional (2D) transition metal dichalcogenides electronic devices are scaled down to the sub-micrometer regime, the active layers of these materials are exposed to high lateral electric fields, resulting in electrical breakdown. In this regard, understanding the intrinsic nature in layer-stacked 2D semiconducting materials under high lateral electric fields is necessary for the reliable applications of their field-effect transistors. Here, we explore the electrical breakdown phenomena originating from avalanche multiplication in MoS2 field-effect transistors with different layer thicknesses and channel lengths. Modulating the band structure and bandgap energy in MoS2 allows the avalanche multiplication to be controlled by adjusting the number of stacking layers. This phenomenon could be observed in transition metal dichalcogenide semiconducting systems due to its quantum confinement effect on the band structure. The relationship between the critical electric field for avalanche breakdown and bandgap energy is well fitted to a power law curve in both monolayer and multilayer MoS2.

Simulation of the Plasma Afterglow in the Discharge Gap of a Subnanosecond Switch Based on an Open Discharge in Helium

The phenomenon of subnanosecond electrical breakdown in a strong electric field observed in an open discharge in helium at pressures of 6–20 Torr can be used to create ultrafast plasma switches triggering into a conducting state for a time shorter than 1 ns. To evaluate the possible repetition rate of such a subnanosecond switch, it is interesting to study the decay dynamics of the plasma remaining in the discharge gap after ultrafast breakdown. In this paper, a kinetic model based on the particle-in-cell Monte Carlo collision method is used to study the dynamics of the plasma afterglow in the discharge gap of a subnanosecond switch operating with helium at a pressure of 6 Torr. The simulation results show that the radiative, collisional-radiative, and three-body collision recombination mechanisms significantly contribute to the afterglow decay only while the plasma density remains higher than 1012 cm−3; the main mechanism of the further plasma decay is diffusion of plasma particles onto the wall. Therefore, the effect of recombination in the plasma bulk is observed only during the first 10–20 μs of the afterglow. Over nearly the same time, plasma electrons become thermalized. The afterglow time can be substantially reduced by applying a positive voltage Uc to the cathode. Since diffusive losses are limited by the ion mobility, the additional ion drift toward the wall significantly accelerates plasma decay. As Uc increases from 0 to +500 V, the characteristic time of plasma decay is reduced from 35 to 10 μs.

Measurement of Characteristic of X-band RF Cavity for 6 MeV Electron Linac

A compact 6 MeV electron linear accelerator (linac), intended to be used as an X-ray source for a dual-head gantry radiotherapy system has been developed. In order to meet the size requirements of the dual-head gantry machine, an X-band radio frequency (RF) technology is used, which facilitates a reduction in the size of the linac, which is nine times smaller than the conventional medical purpose linac using S-band RF technology. Nevertheless, the X-band RF technology requires much higher machining precision and higher-quality surface finish owing to the electrical breakdown phenomena resulting from its small size. After the design was completed, the RF cavity was machined using high-precision machining technology, achieving machining tolerances of ±2 μm, and a surface roughness less than 50 nm. Various RF properties were measured in the fabricated RF cavity by using a network analyzer, and the distribution of the electric field generated in the RF cavity was verified by a bead-pull measurement technique. RF conditioning and beam commissioning experiments were performed, following the fabrication and tuning of the RF cavity.

Ignition of lean and stoichiometric air–propane mixture with a subcritical microwave streamer discharge

Pulse detonation engines are considered to be one of effective propulsion systems for future space missions. Significant efforts are being spent on acceleration of fuel combustion and rising is efficiency. Existing studies have mainly focused on optimizing fuel injection and mixing, repetitive initiation of detonation and integration of detonation tubes with fuel inlets. Understanding of streamer propagation mechanism is of essential importance for the studies of electrical breakdown phenomena and their related applications. In this study, a subcritical microwave streamer discharge is used to initiate ignition of air–fuel mixtures. Ignition of lean fuel mixtures by a streamer has been demonstrated at atmospheric pressure. The speed of streamer-initiated combustion has been shown to be higher compared to that initiated by a spark. The combustion efficiency has also been shown to be higher when using the microwave streamer ignition.

Degradation patterns of silicone-based dielectric elastomers in electrical fields

ABSTRACTSilicone elastomers have been heavily investigated as candidates for the flexible insulator material in dielectric elastomer transducers and are as such almost ideal candidates because of their inherent softness and compliance. However, silicone elastomers suffer from low dielectric permittivity. This shortcoming has been attempted optimized through different approaches during recent years. Material optimization with the sole purpose of increasing the dielectric permittivity may lead to the introduction of problematic phenomena such as premature electrical breakdown due to high leakage currents of the thin elastomer film. Within this work, electrical breakdown phenomena of various types of permittivity-enhanced silicone elastomers are investigated. Results showed that different types of polymer backbone chemistries lead to differences in electrical breakdown patterns, which were revealed through SEM imaging. This may pave the way towards a better understanding of electrical breakdown mechanisms of dielectric elastomers and potentially lead to materials with increased electrical breakdown strengths.

Исследование неполного пробоя диэлектриков и стекла

Works aimed at studying electrical breakdown of solid dielectrics placed in sharply nonuniform fields have revealed a number of interesting phenomena for partial and sequential breakdown cases. The article analyzes the properties pertinent to partial breakdown of dielectrics. Partial breakdown depends on the applied voltage level, time, thickness, and crack length growth rate. When a dielectric is placed in electric field, charges appear on the surface of its air inclusions. Once the field strength caused by these surface charges reaches the breakdown voltage of air inclusions, air ionization processes are initiated. The ionization will take place until air ions have neutralized the surface charges. After that, the cycle is repeated. The ratio between the electromagnetic field attraction and repulsion forces that arise when the atoms approach each other determines the stable existence of a solid body and its mechanical properties, adhesion, and surface tension. Formulas for calculating the adhesion energy are obtained, and the calculation results are presented. The theoretical values of these quantities can be used in performing a comparative analysis of adhesion energy variations for different solid materials. The electrical breakdown of glass coated with an electrically conducting film was investigated. A 2...3 mm wide part of the film was removed by means of a laser to form insulating cut-offs. Such cut-offs on the surface of glass coated with a conducting film and placed in electric field give rise to nonuniformities in electric field distribution. These nonuniformities concentrate over the perimeter of insulation cut-offs and at the corners. To investigate the electrical breakdown of glass, its samples were prepared with various types of cutoff shapes: linear cut-offs and cut-offs with the perimeter of a square or rectangle. The glass plate was laid with its non-coated side facing the breakdown installation’s lower electrode, whereas the upper electrode was placed on the film surrounded by cut-offs or insulated strips without film. The electrical breakdown phenomena were investigated by applying AC voltage. The breakdown occurred over the film periphery at the boundary with cut-offs. It has been found from the experiment that numerous discharges are observed over the boundary between the film and insulating strip during the breakdown. It has also been found that glass melting occurs on the glass surface at the air ionization spots. Experimental data on partial breakdown of glass having different configurations, with and without cut-offs, for glass samples with film coated on one side are presented. It is shown that partial breakdowns in glass occur at field strengths less than those causing the real breakdown, which is characteristic of the gas medium in which the breakdown occurs.

Effect of ambient temperature on electrical treeing and breakdown phenomenon of polypropylene with repetitive pulse voltage

In this paper, the treeing characteristics and breakdown phenomenon of polypropylene (PP) considering different temperatures with repetitive pulse voltage were investigated. The temperature varied from 50 to 130 °C. The pulse amplitude ranging from 15 to 19 kV was applied. The tree initiation probability increases with the increase of temperature and the applied pulse amplitude. With the temperature increasing from 50 to 110 °C, the growth rate of electrical trees increases, while it is the slowest at 130 °C, which is explained by the differential scanning calorimetry (DSC) analysis result. Meanwhile, the growth rate and fractal dimension of electrical trees increase with the increase of pulse amplitude at the same temperature. It is found with the temperature increasing from 50 to 110 °C, the fractal dimension of breakdown electrical trees increases, while it is smaller at 130 °C than that at 110 °C. The accumulated damage of breakdown electrical trees is independent with temperature. By using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDAX), agglomerated and dispersed particles which contain carbon and oxygen elements are observed in the breakdown channels. The chemical analyses of the breakdown channels by attenuated total reflection infrared (ATR-IR) spectrum show that it contains C=O and C-O groups.

Dielectric Breakdown and Failure of Ferroelectric Films as the Dielectric for Electrowetting Systems

In this paper, we study the electrical properties and breakdown phenomena of PZT ferroelectric thin film in electrowetting systems. The experimental results indicate that irreversible charge trapping occurred with repeated voltage actuation, resulting in contact angle relaxation and reduction of the ferroelectric film breakdown strength. The breakdown voltage depends on DC voltage polarity, and this polarity dependence was found to be related to the thickness of the ferroelectric layer. When AC voltage was applied, the breakdown voltage increased directly with voltage frequency. These phenomena are interpreted in terms of electrochemical reactions at the liquid/solid interface, an empirical model was used to estimate the amount of trapped charge in the ferroelectric film.

A new theoretical formulation of coupling thermo-electric breakdown in LDPE film under dc high applied fields

In this paper, we present a new theoretical and numerical formulation for the electrical and thermal breakdown phenomena, induced by charge packet dynamics, in low-density polyethylene (LDPE) insulating film under dc high applied field. The theoretical physical formulation is composed by the equations of bipolar charge transport as well as by the thermo-electric coupled equation associated for the first time in modeling to the bipolar transport problem. This coupled equation is resolved by the finite-element numerical model. For the first time, all bipolar transport results are obtained under non-uniform temperature distributions in the sample bulk. The principal original results show the occurring of very sudden abrupt increase in local temperature associated to a very sharp increase in external and conduction current densities appearing during the steady state. The coupling between these electrical and thermal instabilities reflects physically the local coupling between electrical conduction and thermal joule effect. The results of non-uniform temperature distributions induced by non-uniform electrical conduction current are also presented for several times. According to our formulation, the strong injection current is the principal factor of the electrical and thermal breakdown of polymer insulating material. This result is shown in this work. Our formulation is also validated experimentally.