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![shows the field enhancement factor (FEF, f ) of the two kinds of electrode configurations with Equation (1) [18]:](profile/Liang-Zhao-78/publication/260709164/figure/fig4/AS:897990533324812@1591109035680/shows-the-field-enhancement-factor-FEF-f-of-the-two-kinds-of-electrode-configurations.png)
shows the field enhancement factor (FEF, f ) of the two kinds of electrode configurations with Equation (1) [18]:
Source publication
Based on a nanosecond-pulse generator and dozens of polyethylene samples, the role of electrodes in dielectric breakdown under nanosecond pulses is experimentally investigated. The test factors include electrode material, electrode configuration, and pulse polarity. For the electrode material effect, metals of copper, stainless steel, aluminum, and...
Contexts in source publication
Context 1
... can be seen that the two kinds of results agree with each other. With Figure 4 and the formula for the non-uniform electric field strength: ...
Context 2
... 3) Change the sample thickness and repeat Step 1) and Step 2) to obtain one E BD -versus-d regularity in this condition. Figure 7 shows the E BD -versus-d regularities of the four kinds of electrode by using equation (2) and the values of FEF in Figure 4. From Figure 7, it is clearly seen that E BD for these electrodes conforms to the following relation: ...
Context 3
... can be seen that the two kinds of results agree with each other. With Figure 4 and the formula for the non-uniform electric field strength: ...
Context 4
... 3) Change the sample thickness and repeat Step 1) and Step 2) to obtain one E BD -versus-d regularity in this condition. Figure 7 shows the E BD -versus-d regularities of the four kinds of electrode by using equation (2) and the values of FEF in Figure 4. From Figure 7, it is clearly seen that E BD for these electrodes conforms to the following relation: ...
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Though electro-discharge machining (EDM) is in practical use for the last several decades, still several physical phenomena occurring during machining process are not well understood. For instance, it is well established that for higher material removal rate (MRR) in die sinking EDM of steel workpiece with copper tool the recommended polarity combi...
Citations
... 6 Alternatively, localized electron emission near the ATJ, either from particulates or from the insulator itself, may bring a region of the surface closer to anode potential and introduce sufficiently enhanced fields adjacent to this field-emitting region for the first local breakdown to occur. 2,6 The field required in either of these scenarios is on the order of a few MV/cm, 2,11,12 though it is noted that the required field may be slightly reduced compared to typical nanosecond bulk dielectric breakdown scenarios due to abnormalities in the bulk near the interface. 2 A more recent theory is proposed by Javedani et al. 13 and Lauer, 14 which relies on the creation of a region of strong positive surface charge near the ATJ. ...
Time-resolved optical emission spectroscopy is used to explore the early development of anode-initiated flashover in vacuum. An experimental apparatus for collecting flashover self-luminosity is introduced, which enables spatially resolved light collection from regions adjacent to the anode and cathode triple junctions. The emitted light is spectrally and temporally resolved utilizing an imaging spectrograph and a fast electronic shutter camera. The first light detectable from flashovers across both Rexolite and polytetrafluoroethylene (PTFE) insulators begins less than 10 ns prior to the flashover gap's impedance collapse and consists of faint broadband feature in primarily visible wavelengths. This suggests luminosity due to excitation in the solid, possibly occurring as a result of field emitted electrons. In the few nanoseconds leading up to and including the impedance collapse, the broadband spectrum grows in intensity and extends into the UV, eventually accompanied by a few emission lines of the insulator material. This is strong evidence that the early stages of anode-initiated flashover include surface layer breakdown of the insulator, as a contrast from cathode-initiated flashover, which is predominately an above-surface process. Spectra accumulated over longer exposures of PTFE flashovers indicate that, in the first few hundred nanoseconds after the impedance collapse, ions from the insulator material constitute the majority of the emission lines. Later, neutral and ionic metal species from the electrode contribute with similar prominence as well as molecular bands from diatomic carbon. Finally, a comparison is provided of the results of these studies to other spectroscopic investigations of vacuum flashover from the literature.
... Based on Figures 6(a) and 6(b), it was observed that the impulsive breakdown strengths of the solid interfaces are not only vastly inferior to that of bulk solids (typically in the range of MV/cm, e.g., [32], [33]), but in the majority of cases reduced the system breakdown strength to significantly below that of just air alone. In [16], authors have suggested that the tracking resistance of the interfacial contact spots may be important to determine the overall breakdown strength of a solid interface. ...
With the ever-increasing requirements placed on current and future pulsed power systems in terms of voltage, power, and compactness, solid insulation is a strong candidate for the development of novel insulating systems capable of meeting these specifications. However, the issue of solid-solid interfaces under non-standard and fast-rising impulsesmust firstly be addressed, as the failure to do so may pose significant risk of electrical breakdown due to reduced dielectric strength across interfacial contacts. In this work, the impulsive breakdown characteristics across dry-mate solid interfaces formed between PVC (polyvinylchloride), Torlon (polyamide-imide), Delrin (polyoxymethylene), Perspex (polymethylmethacrylate), and Ultem (polyetherimide) has been investigated in atmospheric air and under two different impulsive waveforms rising at ~2400 kV/μs and ~0.35 kV/μs and in the overstressed breakdown regime. The statistical treatment of the obtained impulsive breakdown voltages and time to breakdowns are presented, alongside an analysis of the post-breakdown surfaces and discharge channel morphologies. The results indicate that under low mating pressure conditions (10’s of kPa), the interfacial breakdown strength may be below that of only an air gap with no dielectrics. A correlation between the estimated asperity aspect ratio and the interfacial breakdown strength has been observed. This suggests that under the present experimental conditions, field enhancement around surface asperities may be a dominating factor which defines the breakdown strength of the interface, since the surface asperities do not deform sufficiently to form strong interfacial contact spots, and thus effectively reduces the interfacial tracking resistance. The widths of post-breakdown traces left by plasma channels on the contacting surfaces have also been shown to be dependent on the rate of voltage rise,
dV/dt
, and on the material forming the interface. The results arising from this work may aid in the future development of high voltage solid insulating systems for power and pulsed power systems.
... The role of the electrode material and the electrode/dielectric interface on injection and extraction of charge carriers has been studied by a few authors, with variable results. Studies focusing on similar dielectrics [71,72] attribute high relevance to the metallization, as it determines the injection and extraction dynamics and consequently the actual electric field distribution inside the sample throughout the polarization. ...
Thin polypropylene films have played a strategic role in recent years because they are the dielectric of choice for high-energy-density and high-power-density DC-link capacitors, and have been extensively used in renewable energy and electric mobility applications. Currently, these capacitors operate at temperatures of up to 105 °C with electric fields of up to 200 V/µm, allowing high efficiency due to their low dissipation figures compared to other capacitor technologies. The rapid evolution of green energy applications demands higher energy and power density, with expected operating temperatures and electric fields of up to 115 °C and above 250 V/µm, respectively. Under such conditions, the insulation resistance of the capacitor becomes a key factor, as it may start to contribute to the dissipation of energy. A correct understanding of conduction phenomena within the dielectric is necessary for the design of new high-performance capacitors based on polypropylene film with reduced conduction losses. The scope of this review is to present and evaluate the theoretical and experimental works on thin biaxially oriented polypropylene (BOPP) films for capacitor applications with a focus on electrical conductivity at high electric field and temperature.
... The voltage amplitude of the pulses of the TPG200 can reach 300 kV. More details about the TPG200 are available in [10][11][12]. A custom-built on-line transmission microscope is also constructed which has a resolution of 0.7 μm and can record images to a PC at a rate of 15 frames per second. ...
xref ref-type="sec" rid="sec1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Section I
of this work proposed a mathematical model and three types of solutions for conductive electrical tree growth in dielectrics. In this section, experiments are presented using a cone-plane electrode and nanosecond voltage pulses to investigate the electrical tree growth in polymethyl methacrylate (PMMA) samples. The results show that the tree length
is proportional to the tangent of the pulse number
under high-voltage pulses but
approaches a limiting length under relatively low voltage pulses. These results agree with those predicted from the model. Therefore, the mathematical model for conductive electrical tree growth in dielectrics is verified.
... The probability of PEB with the electrode arrangement of "pin-plate" electrodes and "pinpin" electrodes cannot be generalized. For "pin-plate" type electrodes, PEB is obviously easier to sprout from the tip of the pin-shaped electrode (Zhao et al. 2012). For the electrode arrangement of "pin-plate" electrodes, the smaller the radius of curvature of the electrode tip, the easier it will be to achieve the loading voltage when PEB occurs (Kuznetsov et al. 2011); the high-voltage electrode terminal is more likely to produce PEB than the ground terminal; the PEB is more likely to occur at the electrode tip when a high-voltage pulse with positive polarity is applied than that when a highvoltage pulse with negative polarity is applied (Phloymuk et al. 2013). ...
With the deepening of the development of natural resources, the difficulty of rock breaking is increasing. Novel efficient rock-breaking technology and matching rock-breaking tools are urgently needed. The high-voltage pulsed fragmentation (HVPF) method has high efficiency and great development potential. So, it has attracted wide attention. However, the unclear understanding of the relationship between the mechanism of HVPF, the design and parameter optimization of HVPF tools, and rock-breaking energy consumption also impede the commercial progress of this technology. In this paper, the electrical crushing is subdivided into “partial electrical breakdown” (PEB) and “complete electrical breakdown” (CEB) from electrical breakdown process (EBP), and the mechanism of PEB is proposed. Finally, a method, which is named as voltage partitioned method (VPM), for designing and optimizing parameters of the HVPF tools is provided. The results of numerical simulation and electrical breakdown experiment can well support the mechanism of PEB. The mechanism of PEB provides a basis for the application of multi-pulse electrical breakdown technology. The VPM establishes the relationship between voltage loading parameters, electrode structure parameters and rock electrical parameters, which can provide reliable help for the design and parameter optimization of HVPF tools.
... (2) A triple junction exists, which means the conjunction of metal, insulator, and gas or vacuum regions. A triple junction may reduce the work function ϕ m of the metal and cause more seed electrons to be injected into the polymer [21]. Thus, to retard the first breakdown channel, we must prevent the seed electron from being injected into the insulator or eliminate the triple junctions. ...
We report on research into methods to improve the lifetime of insulators in multi-stage gas switches exposed to microsecond kV pulses at 20 Hz repetition rate. Two sets of experiments are reported; first on a comparison of polyetheretherketone (PEEK) and polyimide (PI) insulation. The results shows that the lifetime of PI far exceeds that of PEEK, which is attributed to the softening temperature of PI being higher than that of PEEK. In the second experiment, two methods are used to enhance the lifetime of PI; the first is to gild the surface of PI insulators, and the second is to insert PI films between the insulators and the electrodes. Both methods significantly increase the PI lifetime, but the film method leads to a longer lifetime than the gilding method. Imaging the insulator surfaces at the microscopic level reveals that local regions are not smooth, which results in greater electron emission from the cathode. The gilding method lowers electron emission and ejection and the film method blocks electron emission and ejection and thus they enhance the lifetime of PI insulators in multi-stage gas switches.
... Both the material and the configuration of an electrode can influence EBD, as researched in Ref. 74. Figure 17(a) shows the configuration of the electrode system used to determine the effect of the material of the electrode. It comprised a cone with a tip radius of 1 mm and a cylindrical electrode with a radius of 60 mm. ...
... The effects of pulse include those of the polarity and pulse width on EBD and have also been investigated in Ref. 74. ...
... The effect of pulse polarity determines whether there is any difference between EBD for positive and negative pulses at a nanosecond time scale. 74 The relevant experiments were conducted using coneplane electrodes as shown in Fig. 17(a). The test sample was made of PE. ...
The breakdown of polymer insulators at a nanosecond scale is a serious problem for high-voltage devices and pulsed power systems. This paper reviews recent developments in research on the mechanisms and characteristics of the breakdown of polymers at a nanosecond scale at the Northwest Institute of Nuclear Technology. An improved avalanche breakdown model is proposed, and a formula for the strength of the electric breakdown (EBD) is formulated based on it. The formative time lag of the avalanche breakdown model is then developed to verify it. Two research groups were formed to study the characteristics of the breakdown. One focused on the characteristics of single-pulse breakdown, such as the effects of size, polymer type, electrode, pulse width, and pulse polarity on EBD, with the aim of deriving expressions for EBD. The other research group examined cumulative (multi-pulse) characteristics of the breakdown with the aim of deriving a formula for the lifetime of the polymer. A method to design solid insulation structures is finally proposed.
... Many solid dielectric breakdown experiments have been carried out in our laboratory, [16][17][18] and photographs of the breakdown of test samples have been obtained (Fig. 2). It is found that the breakdown traces in dielectrics are conical rather than cylindrical, which supports the breakdown model suggested in this paper. ...
... The dependency of EBD on N 0 is shown in Fig. 3, from which we can see the following: EBD decreases as N 0 increases. This agrees with the experimental observation that an electrode with a lower work function can emit more primary electrons, which corresponds to a lower EBD; see the experimental results of Zhao et al. 18 re-plotted in Fig. 3(b). ...
A formula to calculate the electrical breakdown strength EBD of solid dielectrics is derived based on a model of electron impact ionization and multiplication. This formula takes into account three types of parameters that influence EBD, namely, dielectric parameters (dielectric temperature and atom density), impact ionization parameters (ionization energy and probability), and multiplication parameters (number of initial electrons and number of generations of secondary electrons). The predictions of this formula are found to agree with experimental results. In addition, comparisons are made between the results of this formula and those of 38-generation-electron theory and other models, which show that the proposed formula is most appropriate to describe the breakdown of solid dielectrics on a nanosecond time scale.
... In the dielectric capacitors, factors such as the type of metals used for electrodes and surface resistivity, could affect their electrical properties, especially electric breakdown strength (EBD) [16][17][18]. The relationship between EBD of dielectric capacitors and work function of electrodes have been studied by other researchers [16,17,19]. ...
... In the dielectric capacitors, factors such as the type of metals used for electrodes and surface resistivity, could affect their electrical properties, especially electric breakdown strength (EBD) [16][17][18]. The relationship between EBD of dielectric capacitors and work function of electrodes have been studied by other researchers [16,17,19]. It is concluded that EBD of dielectric capacitors is directly proportional to the work function of metal, which is used for electrodes. ...
Due to the increasing greenhouse gas emissions and gradual run out of fossil fuels, there is a growing concern on the environmental protections and global energy demands in the world. Therefore, new energy storage technologies have been continuously developed to be integrated with renewable energy systems in recent years. Nowadays, advanced composites are popular in automotive and aerospace industries because of their significant advantages such as high specific strength to weight ratio and non-corrosion properties. Therefore, research interests in developing multifunctional composite materials in order to reduce the fuel and energy consumption have increased significantly. Therefore, this paper is focused on the development of multifunctional energy storage systems. The introduction of structural dielectric capacitors and structural electric double layer capacitors (EDLC) are presented. Then, experimental findings, in terms of improvements on the mechanical and electrical properties of structural dielectric capacitors, and factors on the overall performance of structural EDLC conducted by other researchers are given. In addition, it has been proven that the structural dielectric capacitors could maintain their capacitive function under a mechanical loading. Lastly, challenges that would be faced in the realization of structural dielectric capacitors and structural EDLC are discussed.
... Several sub-types of the Tesla-type generators were constructed for different purpose, for example, the Sinus series 4,5 and the Tesla-type pulse generator a) Author to whom correspondence should be addressed: jcsu@mail.xjtu. edu.cn (TPG) [6][7][8][9] series are for high power microwave (HPM) generation, the Radan series, 10,11 and the Chao-Kuan-Pu (CKP) series 12 are for ultra wide band (UWB) generation, some for the long pulse generation, 13,14 some for the dielectric breakdown research, [15][16][17] some for the switch research, 18,19 some for the surface flashover research, [20][21][22] and so on. The secondary winding is one of the key components for the Tesla transformer and for the Tesla-type generators. ...
A compact multi-wire-layered (MWL) secondary winding for a Tesla transformer is put forward. The basic principle of this winding is to wind the metal wire on a polymeric base tube in a multi-layer manner. The tube is tapered and has high electrical strength and high mechanical strength. Concentric-circle grooves perpendicular to the axis of the tube are carved on the surface of the tube to wind the wire. The width of the groove is basically equal to the diameter of the wire so that the metal wire can be fixed in the groove without glue. The depth of the groove is n times of the diameter of the wire to realize the n-layer winding manner. All the concentric-circle grooves are connected via a spiral groove on the surface of the tube to let the wire go through. Compared with the traditional one-wire-layered (OWL) secondary winding for the Tesla transformer, the most conspicuous advantage of the MWL secondary winding is that the latter is compact with only a length of 2/n of the OWL. In addition, the MWL winding has the following advantages: high electrical strength since voids are precluded from the surface of the winding, high mechanical strength because polymer is used as the material of the base tube, and reliable fixation in the Tesla transformer as special mechanical connections are designed. A 2000-turn MWL secondary winding is fabricated with a winding layer of 3 and a total length of 1.0 m. Experiments to test the performance of this winding on a Tesla-type pulse generator are conducted. The results show that this winding can boost the voltage to 1 MV at a repetition rate of 50 Hz reliably for a lifetime longer than 10⁴ pulses, which proves the feasibility of the MWL secondary winding.
