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Dielectrics and Electrical Insulation, IEEE Transactions on

Issue 4 • Date Aug 2001

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Displaying Results 1 - 21 of 21
  • Frequency characteristics of leakage current waveforms of an artificially polluted suspension insulator

    Page(s): 705 - 709
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (440 KB) |  | HTML iconHTML  

    In order to establish a method for monitoring contamination in insulators based on leakage current waveforms and their frequency characteristics, the leakage current waveforms and frequency characteristics of an artificially polluted 180 mm diameter cap and pin type insulator were investigated by the wet contaminant and the clean fog methods at fixed applied voltages. As a result it was found that leakage current waveforms become similar to the symmetrical wave when strong local arcs occur; hence, the intensity of the odd order of harmonic components, e.g. 50, 150, and 250 Hz, is high. Furthermore, it was clarified that the transition of the leakage current waveforms, until flashover occurs, is classified into six stages and that a threshold exists by which the occurrence of flashover can be predicted View full abstract»

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  • Effect of surface treatment on polypropylene film-oil interactions

    Page(s): 710 - 713
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    The results are being presented of an investigation to explore the possibility of using surface modification of biaxially oriented polypropylene (BOPP) film in the control of some polymer-oil interactions. The deposition of thin-film polymer structures by means plasma polymerization of styrene in r.f. glow discharges have been used as a method of polymer surface treatment. The change of some characteristics of polypropylene after treatment and effect of use of plasma polymer coating on polymer-oil interaction as well as on resulting dielectric properties of polymer-oil system have been investigated View full abstract»

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  • Bending piezoelectricity in SAN and ABS copolymer films

    Page(s): 714 - 717
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    The bending piezoelectric coefficients β331 have been calculated (~1.5, 8.3, 10.0 μm) for various cases of unstretched and stretched, unpoled and corona poled, films of SAN. For the ABS films the value of β331~2.6 nC/m was obtained for unstretched and unpoled film, and 4.4 nC/m for corona poled films. A linear relation between β331 and d31 for the heat-treated samples indicates that the major contribution to bending piezoelectricity comes from the dipolar polarization View full abstract»

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  • Electrical and environmental stress and the hydrophobic stability of SIR, EVA and their blends

    Page(s): 679 - 686
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (920 KB) |  | HTML iconHTML  

    This paper treats the effects of electrical and environmental stresses on the hydrophobicity of polymers intended for use in nonceramic insulators. We investigated the effect of UV radiation, corona discharges, dry-band arcing, acid rain and water absorption on hydrophobic transfers in, and the aging of, room temperature vulcanized (RTV)-silicone rubber (SIR), high temperature vulcanized (HTV)-silicone rubber (SIR), ethylene vinyl acetate (EVA) rubber and the blends made from HTV-SIR and EVA. Acid rain had little influence on hydrophobicity in any of the samples. EVA and the blends with low silicone ratios to EVA allowed much larger reduction in hydrophobicity after or while subjected to the above stresses (except for acid rain) than did the silicone rubbers and a blend with a high silicone ratio to EVA. Salt-fog tests were conducted to correlate the hydrophobic stabilities of materials with leakage current levels thereon. The hydrophobic stability of the silicone rubbers was attributed to low-molecular-weight silicone components that were able to migrate and finally cover the aged surface layers. Because EVA possessed less fluid components and less chemical stability under electrical and environmental stresses, its hydrophobicity was readily reduced and hardly recovered, which led to higher current leakage and early material aging. For each material, the critical hydrophobic level permitting leakage current to develop was determined by adding a non-ionic wetting agent to saline water View full abstract»

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  • Space charge measurements in polymeric HV insulation materials

    Page(s): 725 - 730
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    This paper reports on a study using the laser induced pressure propagation (LIPP) method to measure the space charge characteristics in bulk crosslinked polyethylene (XLPE) insulation under dc electric stress. Particular attention has been given to the quantitative appraisal of calibration parameters, and the resultant estimations of space charge and electric stress distributions. A method is described for analyzing the measured raw data from ramp voltage and aging tests to give an estimate of charge and stress without resorting to a complicated mathematical exercise. The consequence of stress enhancement due to the trapped charge on the life of the insulation is estimated using the empirical inverse law. Using analysis of variance and a multivariate analysis technique, the effects of treatment and type of XLPE on the space charge characteristics are also discussed View full abstract»

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  • Finite element based Kerr electro-optic reconstruction of space charge

    Page(s): 612 - 628
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1568 KB) |  | HTML iconHTML  

    Recently we used the onion peeling method to reconstruct the axisymmetric electric field distribution of point/plane electrodes from Kerr electro-optic measurements. The method accurately reconstructed the electric field from numerically generated data. However in the presence of experimental noise the performance was less satisfactory. The measurements were especially noisy and unstable near the needle tip which is also the interesting region since most charge injection initiates here. We develop a new algorithm for Kerr electro-optic reconstruction of space charge in axisymmetric point/plane electrode geometries. The algorithm is built on the finite element method (FEM) for Poisson's equation and will be called finite element based Kerr electro-optic reconstruction (FEBKER) hereafter. FEBKER calculates the space charge density directly to avoid the numerical problems associated with taking the divergence of the electric field, uses single parameter light intensity measurements to enable transient analysis, which otherwise is difficult since multiple parameter intensity measurements are slow due to the rotation of polarizers, and is capable of reconstruction even when the number and/or position of measurements are limited by the electrodes and/or the experimental setup. The performance of the algorithm is tested on synthetic Kerr electro-optic data obtained for an axisymmetric point/plane electrode geometry in transformer oil with specified space charge density distributions. The impact of experimental error is analyzed by incorporating random error to the synthetic data. Regularization techniques that decrease the impact of experimental error are applied. In principle FEBKER is applicable to arbitrary three-dimensional geometries as well View full abstract»

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  • Electromechanical modeling and properties of the electret film EMFI

    Page(s): 629 - 636
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    An electromechanical film can be manufactured with different thickness and elasticity. The thickness for sensor and actuator applications is typically between 30 and 70 μm. The film is modeled using a simplified structure, which shows the reciprocity of the sensor and actuator operation models. The value of the transducer constant depends on the ambient temperature and increases at higher temperatures. During aging the transducer constant begins to decrease permanently at 323 K, but some sensitivity remains even at 333 K. Corona charging that gives a sensitivity value ~200 pCN-1 for HS01 type film is preferred over electron beam charging. The development of such films is aimed at sensor and actuator applications. An interesting field is the active control of sound where flat and efficient microphones and loudspeakers are needed View full abstract»

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  • Forward and inverse parameter estimation algorithms of interdigital dielectrometry sensors

    Page(s): 577 - 588
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    In this paper we extend the continuum model for interdigital dielectrometry sensors and propose a new, direct technique for estimating material electrical properties from measurements. Interdigital sensors consist of alternating pairs of long, thin electrodes on a plane. An ideal model assumes that the periodic structure extends to infinity and the electrodes have no thickness. We extend this ideal analysis to account for the physical thickness of the electrodes. We also present the model in a matrix form which is amenable to linear algebraic analysis techniques. In particular, the `inverse problem' of estimating material properties is formulated as a generalized Eigenvalue problem, which avoids the convergence problems of previous iterative algorithms View full abstract»

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  • Ozone generation in dry air using pulsed discharges with and without a solid dielectric layer

    Page(s): 687 - 697
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (840 KB) |  | HTML iconHTML  

    Energy efficient generation of ozone is very important because ozone is being used increasingly in a wide range of industrial applications. Ozonizers usually use dielectric barrier discharges and employ alternating current (ac) with consequent heat generation, which necessitates cooling. In the present study, very short duration pulsed voltage is employed resulting in reduced heating of the gas and discharge reactor. A comparison of ozone generation in dry air using a coaxial concentric electrode system with and without a solid dielectric layer is reported. Two types of dielectric layers were employed, ceramic and polyvinylchloride (pvc). The effects of peak pulsed voltage (12.5 to 62 kV), reactor length (0.1 to 1 m), pulse repetition rate (25 to 400 pulses per second, pps), gas flow rate (1.5 to 3.0 1/min) and variation of the pitch length of the spiral wire forming the central electrode (5 to 10 mm) on the concentration and production yield of ozone (g/kWh) are reported. A comparison is made between the performance of discharge reactors with (ceramic reactor Type IIC and pvc reactor Type IIP) and without (reactor Type I) a dielectric layer, using the same electrode gap separation (15 mm) and reactor lengths (0.157 and 1 m). High production yields of ozone in dry air of ~125 52 and 60 g/kWh were obtained when using, respectively ceramic, pvc, and no dielectric layer, for a fixed pulse rate of 100 pps, 15 1/min now rate and for a relatively short length of the reactor of 157 mm View full abstract»

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  • On PD mechanisms at high temperature in voids included in an epoxy resin

    Page(s): 589 - 597
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (880 KB) |  | HTML iconHTML  

    In this paper the effects of temperature on partial discharge (PD) activity taking place inside a spherical void in epoxy resin system are studied. Indeed, some experimental tests previously performed on specimens, having different void shapes, under multi-stress condition of temperature and voltage, have shown very different PD amplitude distributions at temperatures higher than ambient. However, this phenomenon cannot be explained only by taking into account the different thermobaric conditions of the enclosed gas. In consequence of the general physical inaccessibility of such voids, a study is here performed using a numerical model based on an evolutionary optimization algorithm. This is used to evaluate the range values for the physical parameters of the insulating system influencing the observed changes in PD activity. Finally, comments are presented about the adopted criteria by which the comparison between the experimental data and the simulated ones is performed, and about the interpretation of the dependence on temperature of the experimental PD View full abstract»

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  • A critical role for the branched sidechain adjacent to the third arginine of the sodium channel voltage sensor

    Page(s): 637 - 643
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (712 KB) |  | HTML iconHTML  

    Molecular dissection of the action potential sodium channel with the peptide strategy pleads for functional and structural asymmetry. The authors previously showed that the different voltage dependencies exhibited by the four isolated S4L45 (from the electric eel sequence) reconstituted into planar lipid bilayers were correlated with the position of a single proline residue and to a conformational transition (from helix to extended forms) occurring with an increase of the solvent permittivity. Ferroelechic liquid crystal properties of residues in an α helix predict a loss of ferroelectric behavior when hydrophobic residues with branched side chains are replaced by residues with unbranched side chains. To test the influence of unbranched side chains, the residues Ile and Leu next to the third and fifth arginines respectively in repeat III were replaced either with α-methylalanine or alanine. The modified voltage sensors were assayed for the voltage sensitivity of their macroscopic conductances, their secondary structure and stability and behavior in analytical ultracentrifugation. Whereas the α-methylalanine analog retained a high sensitivity to voltage changes, but induced longer single-channel events, the alanine substitution (next to the third arginine, R10) leads to a loss of this intrinsic property of the native repeat III, which was correlated with a tendency for dimerization. These results suggest a role for branched side chains of specific residues involved in gating, in agreement with the ferroelectric liquid crystal model View full abstract»

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  • Dielectric study of thin films of Ta2O5 and ZrO2

    Page(s): 648 - 651
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (416 KB) |  | HTML iconHTML  

    Electronic conduction in sputtered Ta2O5 and ZrO2 thin films have been studied using impedance spectroscopy, isothermal transient ionic current, and current-voltage measurements. The dielectric properties of Ta2O5 were shown to be sensitively dependent on deposition parameters with two different frequency responses: a flat loss behavior with very low DC conductivity, or a relaxation peak together with a somewhat higher DC conductivity. ZrO2 has different dielectric properties when fresh, i.e. newly deposited, or aged. A fresh sample arbitrarily can show two different behaviors, consisting of a DC conductivity with a relaxation peak superimposed on it. The DC conductivity shows either of two different values. The aged sample has a lower permittivity and DC conductivity, and the relaxation peak is found at much lower frequencies. Fresh samples of ZrO2 also show switching behavior View full abstract»

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  • Morphology and electrical conductivity in polyaniline/polyolefin blends

    Page(s): 698 - 704
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    The effects of processing and molecular composition on the morphology and electrical conductivity of melt pressed polyaniline (PANI)/polyolefin blends have been investigated. In all systems, the morphology was found to consist of two distinct phases, a conducting network of PANI embedded within the thermoplastic host. Low field conductivities ranging from 10-14 to 10-4 S/cm could be accessed, through a suitable choice of PANI content and processing conditions. To 200 V/mm, the conductivity of the material was found to increase exponentially with applied field, thereafter remaining close to constant until the onset of breakdown. On further analysis, the applied field E dependence of conduction current i prior to breakdown was found to obey a relationship of the form i=A sinh(bE), as reported in the literature for insulators in the so-called low-field regime. Despite the dramatic variations in electrical properties that result from incorporation of the conducting polymer, the low strain mechanical properties were not degraded to any great degree View full abstract»

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  • Identification of a specific type of PD from acoustic emission frequency spectra

    Page(s): 598 - 606
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (816 KB) |  | HTML iconHTML  

    The paper presents an attempt to apply spectral analysis tools in processing acoustic emission (AE) pulses generated by partial discharge (FD). The experimental part of the paper describes spark gaps generating four types of PD and specifies parameters of measured acoustic signals and recalls the system used for measurement and analysis of the frequency spectra. Also, a spectral analysis procedure is presented, and frequency-domain descriptors characterizing AE pulses are defined. The results of the analysis are given both as time plots and amplitude and energy density spectra, related to values of the associated descriptors. The spectral analysis results cover AE pulses generated in systems modeling the following types of pD: point-plane type discharges in oil, surface discharges in oil, gas bubble discharges in oil and discharges in indeterminate-potential particles moving in oil. In conclusion, an ability to identify a specific type of FD on a basis of frequency spectra of AE pulses and their descriptors is presented. The comparative analysis enables one to select those descriptors, which can constitute unique criteria for identification of a specific PD type View full abstract»

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  • Quantitative analysis of structural, relaxational and electrostrictive properties of PVDF-TRFE/PMMA films irradiated with high-energy electrons

    Page(s): 718 - 724
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (496 KB) |  | HTML iconHTML  

    In this paper, the effect of high-energy electron irradiation on the transitional and electromechanical responses of PVDF-TRFE/PMMA (poly (vinylidene nuoride-trinuoroethylene)/polymethylmethacrylate) blend films is investigated in the light of a recent finding of large electrostrictive strain and high electromechanical response of PVDF-TXFE copolymer films after high-energy electron irradiation. Due to the decrease in crystallinity, both the dielectric and polarization responses were found to decrease with PMMA content. Interestingly, the presence of PMMA is found to affect the crystal-amorphous interface properties strongly in irradiated polyblend films. The field-induced strain which could be due to electrostriction and Maxwell stress for a blend system is found to come mainly from electrostriction. At room temperature, the contribution to the total strain from the Maxwell stress is found to be <20% while this contribution increases markedly with increasing temperature, especially for 7 %wt PMMA polyblend films View full abstract»

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  • Tracking and erosion of HTV silicone rubbers of different thickness

    Page(s): 673 - 678
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (520 KB) |  | HTML iconHTML  

    Tracking and erosion behaviors of high temperature vulcanized (HTV)-silicone rubber (SIR) of 0.5 to 6.0 mm thicknesses were investigated in order to obtain the optimum thickness for enhancing tracking and erosion resistance under various leakage current levels. Under low leakage current, thinner samples showed a higher tracking and erosion resistance, while under medium and high leakage current, thicker samples showed better resistance to these behaviors. The optimum thickness to prolong the time to tracking and erosion failure appeared in the range of 1.0 to 3.0 mm thickness. The content of an initial low molecular weight (LMW) silicone fluid was shown to be closely related to the development of leakage current and high temperature thermal spots. The results indicate that the sample thickness is crucial to the ability of HTV-SIR to withstand a large number of high temperature thermal spots under condition of high level leakage current View full abstract»

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  • A probabilistic analysis of spark paths in point/plane air gaps

    Page(s): 644 - 647
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (320 KB) |  | HTML iconHTML  

    Analysis of data derived from sparks in point/plane gaps ranging from 45 to 400 mm has shown the similarity of the probability functions determining the shape of the spark paths. This is true, regardless of gap width, when each path is divided into equal steps, here 2% of the gap width. The probability functions were used to develop improved simulations of the spark paths. The simulations had been seen previously to give visually similar tracks, but in this work improved simulations are shown to give similar values for the small amount by which the spark paths are, on average, displaced when the pointed electrode is tilted. The same agreement was found for the degree of scatter of the spark paths about the mean. It is anticipated that the simulations can be generalized to a variety of geometries and scaled up, to simulate and predict lightning strike probabilities View full abstract»

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  • Streamer current in a three-electrode system

    Page(s): 665 - 672
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (728 KB) |  | HTML iconHTML  

    A study has been conducted on positive streamer discharges in air at atmospheric conditions for a three-electrode system, The electrode system consisted of two parallel planes (one grounded and one supplied with a negative dc voltage) and a small, insulated needle, sticking out from the center of the grounded plane. A triggering positive square impulse voltage of 5 μs duration was applied to the insulated needle and the currents associated with the streamer discharge were measured simultaneously on all three electrodes. During the streamer propagation, the current measured at the needle was the conduction current while the other two were the displacement (or capacitive) currents generated by the movement of charge in the electrode gap. The objective of this study is to identify the three currents and to investigate if simple representations of the streamer can reproduce the displacement currents measured at the plane electrodes. Two models for the streamer were applied: (1) a charged sphere moving in the background field and (2) a channel with a constant voltage gradient extending in the gap. In both models it was assumed that the streamer propagated with a constant velocity, which was estimated from the measurements. The motion of the streamer was simulated by a series of electrostatic calculations, using a field calculation program. Comparison of the measurements with the simulations indicates that the charge of the streamer is confined to a spherical region (i.e. streamer head) and it is increasing continuously during its advancement in the electrode gap. A discussion on advantages and disadvantages with the two investigated models (sphere vs. channel with potential gradient) is conducted, and a possible hybrid model is suggested. In the proposed model, features from both considered streamer representations are included View full abstract»

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  • Electrical strength of air containing ozone and nitric oxides produced by intensive partial discharges

    Page(s): 607 - 611
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    Internal arcing test results of gapped SiC arresters are presented. During a test in which the arrester is exposed to internal arcing, the positive impulse breakdown voltage increases. Measurements made with a model arrangement indicate that the increase in the electrical strength of gas is higher for positive than for negative impulse polarity. When the internal discharges extinguish, recovery processes occur. Additional phenomena that can cause changes in the electrical strength are discussed View full abstract»

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  • Detection and localization of interturn fault in the HV winding of a power transformer using wavelets

    Page(s): 652 - 657
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    One of the standard tests carried out on a power transformer is the lightning impulse, to corroborate the integrity of its winding insulation. The existing transfer function method used for diagnostics lacks sensitivity in detecting minor internal faults. Hence a new approach using `wavelet transforms' is developed to analyze the non-stationary neutral current signal which varies due to the existence of a fault, This approach involves the choice of a basis function applied on the neutral current signal and analyzed in the time-frequency domain. The effectiveness of the approach is that the exact instant of fault occurrence is directly known, such that its actual location in the winding can be predicted easily. This paper presents the approach to simulated interturn fault at three selected locations in the partially interleaved HV winding of a 50 MVA, 400/11.5 kV station transformer such that its performance is recognized. Minor faults, such as one turn short, are simulated and successfully detected using this approach. The results are in good conformity with the theoretical calculations based on the length of the conductor involved and the wave propagation velocity View full abstract»

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  • Very fast transient overvoltages in GIS with compressed SF6 -N2 gas mixtures

    Page(s): 658 - 664
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (608 KB) |  | HTML iconHTML  

    This paper discusses the characteristics of very fast transient overvoltages (VFTO) in SF6-N2 gas mixtures at different percentages of SF6. A comparison of the VFTO characteristics of pure SF6 with those of pure N2 is also presented. The investigations are performed using a laboratory model GIS bus duct having a test gap used for simulating a switching event leading to the generation of VFTO. A capacitive voltage sensor is used to measure the VFTO peak magnitude and temporal characteristics. Measurements were carried out at two different gap spacings (0.20 and 0.61 mm) over a pressure range of 100 to 500 kPa. VFTO characteristics for N2, SF6 and SF6-N2 mixtures obtained from the experiments show similar trends. The level of surge peak magnitude is <2.0 pu for all cases when the gap was 0.20 mm, but it reaches a maximum of 2.41 pu at 0.61 mm gap. At 0.20 mm gap, in SF6-N2 mixtures, the difference in peak magnitudes is not significant for 10% and 20% SF6 mixtures (between 200 and 400 kPa) and also for pure SF6 and 40% SF 6 (between 200 and 300 kPa). The occurrence of corona stabilization during breakdown of the gap may be the cause for such a behavior. Unlike the above observations at 0.20 mm gap, at 0.61 mm gap, the peak magnitudes strictly increase with pressure for the pure gases and gas mixtures. At 0.20 mm gap, the time to breakdown of the gap is found to be almost constant in all cases. But at 0.61 mm gap, the time to breakdown is seen to be dependent on the mixture, pressure, and breakdown voltage, and this observation is in accordance with Toepler's spark law View full abstract»

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Aims & Scope

IEEE Transactions on Dielectrics and Electrical Insulation contains topics concerned with dielectric phenomena and measurements with development and characterization of gaseous, vacuum, liquid and solid electrical insulating materials and systems.

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Reuben Hackam