Initiation Of Electrical Breakdown Research Articles

Effect of shock vector/polarization vector configuration on the generation of ultrahigh voltage by adiabatically compressed ferroelectric materials

Compact autonomous megawatt-power systems based on shock depolarization of ferroelectric materials are capable of producing kiloampere currents and ultrahigh-voltage pulses with amplitudes exceeding 100 kV. Herein, we report the results of experimental investigations of the generation of ultrahigh voltage by poled Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 and Pb0.99(Zr0.52Ti0.48)0.98Nb0.01O3 ferroelectrics subjected to shock loading at different shock vector/polarization vector configurations. Our experiments demonstrated that under loading perpendicular to the polarization vector (transverse stress mode) the ferroelectrics are capable of generating high voltages exceeding 400 kV, while the loading parallel to the polarization vector (longitudinal stress mode) causes a distortion of the depolarization process in ferroelectrics of large thicknesses, resulting in inefficient generation of ultrahigh voltage. It was shown that for transverse semi-planar shock waves, the presence of the longitudinal component of stress due to non-perfect planarity of the shock front can cause a complex electric field distribution in the shock front area, resulting in energy losses in ferroelectrics operating in the ultrahigh-voltage mode. The important finding is that a cylindrical, radially expanding shock wave results in no significant distortion of the depolarization process and energy losses during ultrahigh-voltage generation by transversely shock-compressed ferroelectrics. The experimental results indicate that the voltage amplitude generated by transversely shock-compressed ferroelectrics is directly proportional to the ferroelectric thickness in the range from 6 to 230 mm. We found that over the full range of investigated thicknesses the breakdown-field-on-thickness dependence of shocked ferroelectrics is described by a power law and the mechanism of initiation of electric breakdown does not significantly change with ferroelectric thickness.

Through-plane high thermal conducting networks via incorporation of graphene nanoplatelets in nanocomposite film under electric field and avoiding breakdown voltage

Electric field inducement technology is one of the most efficient and straightforward way to direct and form a percolation network of conducting fillers in a polymer without necessitating chemical functionalization. However, extended application is very restricted due to the initiation of electrical breakdown of conducting fillers in polymers. Herein, thermal conductive polymer nanocomposites are fabricated using graphene nanoplatelets (GNP) as a conducting filler under application of electric field that avoids electric breakdown. An electrode surface is coated with fuluoacrylate of nano-to-micro-dimensional thickness, which is applied as insulating electrodes to inhibit electric spark under application of electric current. Two different kinds of electric fields; direct current (DC) and switching DC (SWDC), were applied to envisage the enhancement of filler assembly. Analysis showed that an insulating layer with approximately 0.35–18 μm of thickness was successfully coated on the electrodes, which enabled increased formation of through-plane thermal conducting networks as well as enhanced thermal conductivity compared to composites with random filler distribution. The intensity of the available electric field could be increased over 30 times without breakdown with the insulating layer. Moreover, the field-induced GNP assembly generated by SWDC improved the thermal conductivity of the composite of over 112% compared to composite with random GNP distribution. This technique has the potential to control the linear assembly of conducting fillers an under electric field without electric breakdown.

Сверхвысокочастотный пробой воздуха, инициированный помещенным на диэлектрической поверхности электромагнитным вибратором

New results of experimental investigations of the possibility and conditions of initiation of electric breakdown of air in a quasi-optical microwave beam with a subcritical field level are described. The breakdown is initiated by a linear electromagnetic (EM) vibrator placed in a traveling EM wave on the surface of the dielectric sheet facing toward the wave vector k, on its opposite surface and near it. Simultaneously, theoretical calculations of the induced electric field near its ends were carried out for all variants of the vibrator location considered in the experiments. Numerical estimates and experimental results have shown that the placement of the vibrator on the surface of a dielectric plate can initiate a breakdown of air at significantly lower levels of the EM field in the microwave beam compared to the case of placing the vibrator in “free space”, i.e.at the absence of any dielectric plates

The Application of a Small-Volume Neon-Filled Tube in Overvoltage Protection

To validate the performance of a small-volume neon-filled tube in overvoltage protection, the characterization of the neon-filled tube at p = 6.6 mbar and with 1-cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> volume was performed. The characterization was performed using the mean value of electrical breakdown time delay t̅ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> data as a function of relaxation period τ, applied voltage Uw, and discharge current I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> . On the basis of t̅ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> data as a function of τ, it was shown that after discharge, the gas full recovery appears for τ ≈ 7 ms. The increase in the applied voltage in the case of full gas recovery leads to the decrease in t̅ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> and for U <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">w</sub> ≥ 130 V, t̅ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> ≈ constant. This proves the tubes efficient usage in overvoltage protection for applied voltages higher than 130 V. The increase in discharge current leads to the decrease in t̅ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> in a considered τ interval. Other important processes that occur in discharge and afterglow, which are responsible for the initiation of electrical breakdown in neon-filled tube, were also analyzed.

Processes responsible for electrical breakdown initiation in commercial indicator gas tube

The results of the commercial indictor gas tube inv estigation, by the time delay measuring method are presented in this paper. This tube is usually used as a indicator of many electrical appliances. The experimentally obtained time delay distributions fo r different voltages (80 V, 90 V and 100 V) and different relaxation times (from 1 ms to 20 ms) are presented. It is shown that time delay distributio ns have Gaussian shape, and that used gas discharge tu be has very small memory effect. Small memory effect indicates fast response, and consequently go od characteristic for indicator tube.

Processes in afterglow responsible for initiation of electrical breakdown in xenon at low pressure

AbstractThe processes responsible for initiation of electrical breakdown in xenon-filled tube with two spherical iron electrodes at 2.7-mbar pressure have been analyzed. The analysis is based on the experimental data of electrical breakdown time delay as a function of afterglow period. It is shown that positive ions remaining from previous discharge, as well as positive ions created in mutual collisions of metastable atoms in afterglow, have a dominant role in secondary emission of electrons from the cathode which lead to initiation of breakdown in early afterglow. In late afterglow, dominant role in initiation of breakdown is taken by N(4S) atoms formed during the discharge by dissociation of ground state nitrogen molecules that are present as impurities in xenon. When the concentration of N(4S) atoms decreases sufficiently, the initiation of breakdown is caused by cosmic radiation. Small doses of gamma-ray irradiation also contribute to the initiation of breakdown, but only for large values of the afterglow period.

Monte Carlo Simulation for an Electrical Discharge in O&lt;sub&gt;2&lt;/sub&gt;

The generation of plasmas and the initiation of electrical breakdown are realized by the phenomenon of electrical discharge which is provoked when we apply a sufficient electric field in a gas. Consequently the free charges are accelerated, new charged particles are created and others are destructed. This can be ranged in four phenomena: elastic collision (recombination), attachment, excitation and ionization. The aim of this paper is to study the basic phenomena in an electrical discharge in the case of Oxygen O2. Monte Carlo Simulation is used to follow the random trajectory of free charges determining in each path many parameters of the discharge. To determinate electrical and physical parameters, we have used the sampling laws. The spatial distributions of space charges (electrons, positive and negative ions) are also obtained. The determination of electrical field depends on distributions of charged particles obtained by solving the Maxwell equations.

Stability and current behaviour in semiconductor gas discharge electronic devices

Breakdown and range of stable discharge glow in a homogeneous dc electric field are studied at various distances d between the electrodes and different inner diameters D (5, 9, 12, 18 and 22 mm) of GaAs semiconductor cathode areas. The current–voltage characteristics of the gas discharge system have been studied in a wide range of pressure p (16–760 Torr), interelectrode distances d (10 µm–5 mm) and conductivities of the GaAs cathode. The initiation of electrical breakdown as a result of secondary electron emission from the semiconductor cathode in low gas pressure is presented in this paper. In a planar gas discharge cell with diameters much larger than an interelectrode distance, the effects of different parameters (overvoltage, electrode separation, diameter and conductivities of the GaAs cathode, gas pressure, glow current, etc) on electrical breakdown and spatial stabilization of the current have been studied. The distributed resistance of photosensitive semiconductor cathode and the impact of the ionizing component of the discharge plasma on the control of the stable operation of a planar gas discharge system at atmospheric pressure are also investigated. Through spatially uniform irradiation of the semiconductor cathode, non-stationary states which are non-homogeneous can be generated in a system. The loss of stability is primarily due to the formation of a space charge of positive ions in the discharge gap which changes the discharge from the Townsend to the glow type.

Investigations of breakdown voltage and time delay of gas-filled surge arresters

The contributions of positive ions and neutral active particles, remaining from previous breakdown and discharge as well as contribution of gamma photons from and radiation sources and cosmic rays to the electrical breakdown initiation in commercial gas-filled surge arresters have been analysed. This analysis was performed on the basis of time delay mean value as a function of afterglow period τ (‘memory curve’) and the breakdown voltage mean value as a function of τ. The values of static breakdown voltage were estimated on the basis of the experimental breakdown voltage data as a function of voltage increase rate using a linear polynomial fit.

Electronic conduction and breakdown in liquid helium and liquid neon

New data of the electronic properties of liquid helium and liquid neon are discussed with respect to their relevance for the initiation of electric breakdown. It is concluded that under ideal conditions the cathode plays a decisive role in the initiation of the breakdown process. It is speculated that a Townsend type breakdown mechanism is absent in the liquid phase of these elements.

Analysis of mechanisms which lead to electrical breakdown in argon using the time delay method

The mechanisms leading to initiation of electrical breakdown in geometrically identical argon-filled tubes at different pressures were investigated by the memory curves. It was shown that the positive ions and metastable states, remaining from the previous discharge, have the dominant role in the initiation of breakdown in early and late afterglow periods, respectively. Contributions to the breakdown of gamma photons from radioactive sources (60Co) and cosmic rays were also analyzed.

Efficiency of copper and gold cathode in initiation of secondary emission in nitrogen-filled tube

The efficiency of secondary electron emission induced by ions and atoms remaining from previous discharge during the initiation of electrical breakdown in a nitrogen-filled tube with bulk copper and gold plated electrodes has been investigated. This investigation was done by measuring the electrical breakdown time delay as a function of afterglow period τ, glow current i g and electrode gap d. The results show that the gold plated cathode is more efficient in secondary electron emission caused by nitrogen atom impact on its surface than that of bulk copper. This phenomenon can be explained by different adsorption ability of nitrogen atoms on the copper and gold surface.

Nanometric dielectrics

It is suggested that a major field of study in the future development of dielectrics will concern their properties when relatively few molecules are involved. Such smallness arises naturally at interfaces of nanometric thickness and will occur also when dielectrics are employed in the nano-technical devices of the future. It already occurs in living systems where the dielectric and conductive properties of biomaterials are vital in sustaining activity. The transverse and lateral properties of interfaces, including the effects of molecular ordering, are considered and it is suggested that the advent of scanning tunneling and atomic force microscopies provides a significant opportunity for nanometric dielectric studies. An important feature, suggested for future exploitation, is the cross-coupling in interfaces of force fields arising from electrical, mechanical, chemical and entropic potential gradients. Application of these concepts to biology and to the behavior of polymer gels which may lead to development of muscle-like actuators and transducers are considered. Finally, attention is drawn to the likely role of nanometric interfacial processes in the initiation of electrical breakdown in insulating materials. >

The electrically ruptured area of crosslinked polyethylene

The electrically ruptured areas of failed crosslinked polyethylenes have been investigated using optical microscopy and Fourier transform infrared spectroscopy (FTIR). The formation of well-defined banded spherulites was observed around the ruptured areas. Since spherulites do not occur in crosslinked polyethylenes, the formation of spherulites in failed specimens is considered to be related to breakage of the network during the breakdown process. FTIR results are shown to support this suggestion, revealing that more than oxidation occurred during the breakdown process. This observation contradicts some well-established breakdown mechanisms, such as thermal breakdown. It is also shown that, if the initiation of electrical breakdown involves network rupture, the properties of crosslinked polyethylene could be enhanced by designing less reactive crosslink points. >

Charge exchange processes at the interface of a metal oxide with a dielectric liquid

Processes by which positive ions are neutralized at a metal-vacuum interface are described. Assuming that similar processes apply to the neutralization of positive ions at the interface of a metal oxide with a dielectric liquid, the authors consider the viability at such an interface of a layer of positive ions. This is often postulated as the first condition in the initiation of electrical breakdown in the liquid. >

Initiation of Electrical Breakdown by Ionic Bombardment in a Vacuum Gap after Arc Extinction

This report presents a theoretical model of development of the post-arc gap breakdown in vacuum as a result of surface processes following cathode bombardment by energetic ions flowing from residual plasma after zero arc current. The most important surface processes for this model are sputtering and secondary electron emission. For a considerable group of metals, the sputtering yield Sr and secondary electron emission γc can assume relatively high values when the ions have a high energy. Based on the ion flux from the plasma and the time of its flow as well as the ionization of sputtered atoms, a quantitative criterion for a breakdown will be derived. It has been proven that breakdown will occur if there is at least a minimum ion charge Qi which is dependent on the product of Sr · γc. Qualitative consistency was also demonstrated between experimental results and the conclusion derived from our breakdown criterion.

Comments on the role of space charges in initiation of electrical breakdown of vacuum gaps

The process of beam spreading of field-emission electrons under the action of space charges, suggested by Maitland (1961) as an explanation of vacuum breakdown initiation, is analysed. This type of space charge effect is shown to be negligible. A plausible model of breakdown initiation as a result of ions focusing within the electron beam is discussed and shown to be unreal. The effects of space charges on the initiation of vacuum breakdown are thus concluded to be very small.

Initiation of Electrical Breakdown of Soil by Water Vaporization

The predictions of a simple model of water vaporization in soil are determined and compared with previously published data for the time for the initiation of streamers which leads to soil breakdown under pulsed high-voltage excitation. This model is capable of predicting the relatively long initiation times which have been observed under certain experimental conditions and also provides an explanation for the strong, experimentally determined, dependence of the initiation time on electric field.

Initiation of electrical breakdown in vacuum

The mechanisms of electrical breakdown in high vacuum have profound implications for the design of high-voltage equipment. Electron emission and microparticle initiated breakdown and simulation studies are outlined and innovations to be incorporated in future high-voltage technology are suggested

Initiation of electrical breakdown in vacuum

Measurements of prebreakdown current as a function of applied electric field have been made for molybdenum electrodes of unlike surface finish in ultra-high vacuum (10−9 Torr), for a fixed gap separation d = 0·05 cm. Two sets of electrodes were used: unpolished anode, polished cathode; and polished anode, unpolished cathode. The prebreakdown currents are found to be consistent with the Fowler-Nordheim field emission theory. The breakdown voltage, the field enhancement factor, the current, and the current density and emitting area at breakdown are given as a function of the number of breakdowns. Also, the critical field enhancement factor, the temperature of the anode hot spot and the cathode microgeometry are calculated. Results indicate that the state of the anode surface governs the breakdown voltage and the microgeometry of the cathode surface. Also, in a conditioned gap both anode and cathode are involved in the discharge initiation. Anode initiation is only obtained with a certain set of electrodes.