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Dielectrics and Electrical Insulation, IEEE Transactions on

Issue 2 • Date Apr 1994

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Displaying Results 1 - 20 of 20
  • Creepage discharge propagation in air and SF6 gas influenced by surface charge on solid dielectrics

    Publication Year: 1994 , Page(s): 294 - 304
    Cited by:  Papers (4)
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    Influence of surface charging on creepage discharge propagation in air and SF6 gas was investigated. The authors have employed a surface charging system using corona discharges, which permitted the deposition of surface charge on solid dielectrics with a given density distribution. By applying a lightning impulse across the charged surface of polyester film, they measured the discharge extension length as a function of surface potential generated by the surface charge. It was found that the impulse creepage discharges along the charged surface under a potential of 2 to 3 kV, extended a distance which was maximum 6× longer than the case of the uncharged surface both in air and SF6 gas. Experimental results were also discussed from the viewpoint of the specific capacitance, permitting their application to actual HV apparatus such as GIS View full abstract»

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  • Artificial neural networks for recognition of 3-d partial discharge patterns

    Publication Year: 1994 , Page(s): 265 - 275
    Cited by:  Papers (21)
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    Partial discharge (PD) measurements have been carried out over the years to assess insulation systems in power apparatus for their integrity and design deficiencies. Digital PD recording, processing and its presentation as 3-d patterns are recent trends in both industry and testing laboratories. Interpretation of these patterns can lead to evaluation of the cause of PD. A need arises to look for methods in the domain of pattern recognition for automating this process. In this context, this paper presents results to demonstrate the possibility of using pattern recognition capabilities offered by a multilayer neural network to recognize 3-d PD patterns View full abstract»

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  • Assessing the risk of failure due to particle contamination of GIS using the UHF technique

    Publication Year: 1994 , Page(s): 323 - 331
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (684 KB)  

    The ultra high frequency (UHF) technique has been used to study the partial discharges produced by free conducting particles in gas insulated substations (GIS) with a view to predicting the probability of particle-triggered breakdown. Statistical techniques have been developed to describe the motion of a single particle. It is possible to identify whether the particle is capable of crossing to the busbar, which is a necessary condition for particle-triggered breakdown. In addition, the technique can be used to assess the size of the particle, which is useful for making a qualitative assessment of the breakdown risk. The implications for the continuous discharge monitoring of GIS are discussed View full abstract»

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  • Influence of voltage and load current on dc bipolar corona pulses

    Publication Year: 1994 , Page(s): 284 - 293
    Cited by:  Papers (3)
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    Digitizing oscilloscopes were used to observe anode and cathode corona pulses on a laboratory scale HVDC bipolar transmission line. Data was collected with the transmission line energized at a nominal voltage of ±60 kV with no load current. The effects of increased voltage and added load current were then separately investigated. Histograms show distributions of corona pulse amplitude and time between consecutive corona pulses (corona pulse time separation). Increasing the transmission line voltage had the effect of increasing corona pulse amplitude and decreasing corona pulse time separation for both anode and cathode. Addition of load current decreased the corona pulse amplitude and increased the corona pulse time separation for the anode. The cathode corona pulse amplitude and pulse time separation decreased with the addition of load current View full abstract»

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  • A new methodology to obtain accurate models for ferroelectrics with application to BaTiO3

    Publication Year: 1994 , Page(s): 196 - 212
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    A new methodology based on semi-infinite optimization is proposed to obtain accurate yet simple phenomenological models for ferroelectric single crystals. The phenomenological models for ferroelectrics start with a Taylor series expansion of the governing thermodynamic potential, the elastic Gibbs function, in terms of the independent variables. The coefficients of the appropriately truncated series are determined, based on the experimental properties of the crystal. However, there is to date no method to determine the coefficients for an accurate correlation to the experimental measurements. To this end, a semi-infinite optimization problem is formulated, aiming at minimizing the error between the analytical model and experiments in terms of permittivity coefficients and spontaneous polarization. A model in the cubic and the tetragonal phases for barium titanate (BaTiO3) single crystals for a particular choice of experimental measurements is used to demonstrate the workability of the proposed methodology. The resulting optimization problem has an infinity of inequality constraints. The optimal solution to the proposed semi-infinite optimization problem when used in the model, accurately predicts the ferroelectric properties of BaTiO3 single crystals such as phase transitions, spontaneous polarization, permittivity, the range of temperature in the cubic and the tetragonal phase. The proposed methodology is not limited by the complexity of the phenomenological model, or the choice of the experimental measurements. Furthermore, the proposed methodology can be generalized to model ferroelastic materials View full abstract»

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  • Injection of a minimal space charge as mechanism for the initial phase of electrical polymer degradation

    Publication Year: 1994 , Page(s): 231 - 234
    Cited by:  Papers (3)
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    In this paper we present a model for polymer degradation during high-field stresses in analogy to the charge-to-breakdown concept in SiO 2. The model is based on space charge injection under high fields which leads to a cumulative effect as in radiation damage. A critical total injected charge density Qc is introduced, which is needed prior to any permanent damage. The assumption of a critical injection level explains the time and field dependence of the tree initiation time. The model is applied to electrical aging experiments in epoxy resins. It turns out that the critical charge for tree initiation is ~10 C/cm2 similar to the value for trap creation in SiO2 gate oxides View full abstract»

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  • Electrical conduction in polyethylene with semiconductive electrodes

    Publication Year: 1994 , Page(s): 224 - 230
    Cited by:  Papers (19)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (492 KB)  

    The electrical conduction characteristics of polyethylene with semiconductive electrodes have been investigated at electric fields of 10 to 600 kV/cm and at temperatures of 25 to 100°C. It was found that the conduction characteristics of the polyethylene were influenced not only by the constituents of the polyethylene but also the electrode materials. Space-charge-limited conduction was found to be the major conduction mechanism in all cases. Differences between conduction characteristics depending on the constituents of the XLPE are described and their causes are discussed View full abstract»

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  • Influence of switching on dielectric properties of vacuum interrupters

    Publication Year: 1994 , Page(s): 340 - 347
    Cited by:  Papers (8)
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    This paper deals with the influence of switching operations `closing without current/breaking without current', `closing without current/breaking with rated current', and `closing without current/breaking of rated short-circuit current' on vacuum interrupter dielectric strength. Two types of commercially available vacuum interrupter with transverse magnetic field CuCr contacts were tested. Breakdown voltages and emission currents, which appear before and after switching operations, were determined experimentally. The corresponding characteristics were determined after conditioning. The voltage shapes, dc, lightning impulse voltage (1.2/50 μs), and 50 Hz ac were applied. The obtained results were statistically treated. After taking into account theoretical considerations, it was concluded which physical mechanisms determine the influence of switching operations on the dielectric strength. It was found that in interrupters with poor contact material, the dielectric strength can deteriorate below the limits required by standards View full abstract»

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  • Streamer propagation over a liquid/solid interface

    Publication Year: 1994 , Page(s): 348 - 350
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    Danikas discusses and comments on a paper by Atten and Saker (see ibid., vol. 28, no. 2, pp. 230-42, 1993). He points out that, using a similar point/plane electrode arrangement and different insulating oils (dodecylbenzene oil and polybutene oil), he reached mostly the same conclusions regarding creepage discharge figures. He also discusses inception electric stress and streamer discharges. In reply, Atten and Saker thank Danikas for his comments and acknowledge the points he raises View full abstract»

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  • Application of artificial neural networks for optimization of electrode contour

    Publication Year: 1994 , Page(s): 254 - 264
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (720 KB)  

    In this paper artificial neural networks (NN) with supervised learning are proposed for HV electrode optimization. To demonstrate the effectiveness of artificial NN in electric field problems, a simple cylindrical electrode system is designed first where the stresses can be computed analytically. It is found that once trained, the NN can give results with mean absolute error of ~1% when compared with analytically obtained results. In the next section of the paper, a multilayer feedforward NN with a back-propagation algorithm is designed for electrode contour optimization. The NN is first trained with the results of electric field computations for some predetermined contours of an axisymmetric electrode arrangement. Then the trained NN is used to give an optimized electrode contour in such a way that a desired stress distribution is obtained on the electrode surface. The results from the present study show that the trained NN can give optimized electrode contours to get a desired stress distribution on the electrode surface very efficiently and accurately View full abstract»

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  • Influence of surface microstructure on the electric and spectroscopic characteristics of dielectric surface flashover

    Publication Year: 1994 , Page(s): 315 - 322
    Cited by:  Papers (7)
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    Spectroscopic investigations were performed on high purity polycrystalline alumina in vacuum to understand the effect of surface microstructure as altered by mechanical surface treatment, on the optical as well as the electrical characteristics of dielectric surface flashover. HV pulses were applied to unpolished samples as well as to samples subjected to mechanical polishing by using SiC (268 to 16 μm) and diamond abrasives (15 to 0.25 μm). The samples finished using diamond paste exhibited lower conditioned voltages and holdoff strength than those prepared with SiC abrasive finish. The spectrum of diamond-finished samples showed early development of molecular bands associated with the dielectric material. This behavior could be due to a larger density of defects developed on the surface during final polishing with diamond paste. There seems to be a correlation between the electrical performance of a sample, the polishing medium used for its surface finish, and the development of some of the spectral lines from flashover. The experimentally-observed phenomena in the studies point to different phases of surface conditioning, in which the dominating factors for the origin of surface flashover seem to depend on the surface state of the insulator View full abstract»

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  • Partial discharge measurements in SF6 and air using phase-resolved pulse-height analysis

    Publication Year: 1994 , Page(s): 276 - 283
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (472 KB)  

    Carries out a study on partial discharge (PD) phenomena in SF6 gas and tries to construct a diagnostic system capable of separating noise from observed PD signals for assessing the condition of insulation performance in power apparatus. The authors have constructed a computer-aided PD measuring system which permits a time-sequential data acquisition and phase-resolved pulse height analysis. Using the PD measurement system, the authors measured 60 Hz AC PD in SF6 gas and in air at atmospheric pressure for needle-plane electrodes with three different radii at the tip of the needle, 3, 30 and 500 μm. They proposed particular PD statistical parameters, unbalance ratios U T and Uq of the pulse repetition rate and average of charge, respectively, between positive and negative PD pulses occurring per cycle; these parameters proved to be good indicators to distinguish PD occurring in SF6 from that in air. The mechanism of PD inception was also discussed View full abstract»

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  • Pulsed electroacoustic method for measurement of charge accumulation in solid dielectrics

    Publication Year: 1994 , Page(s): 188 - 195
    Cited by:  Papers (96)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (576 KB)  

    This paper describes the principle of the pulsed electroacoustic (PEA) method, which was developed a few years ago for profiling the space charge distribution in an acoustically homogeneous solid material. Initially the PEA method could indicate the space charge distribution in the materials only indirectly. Some data processing, for example deconvolution, was necessary to obtain the charge profile. Some very important improvements were made recently to the PEA method which eliminated the need for deconvolution. This paper describes the latest improvements and the practical construction of the detecting electrode system under which the output signal is linearly proportional to the space charge distribution. Nowadays the PEA method can be used to measure the space charge distribution with or without DC electrical stress, not only in free-standing dielectric plates but also directly in coaxial cables View full abstract»

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  • Charge trapping and conduction in pure and iodine-doped biaxially-oriented polypropylene

    Publication Year: 1994 , Page(s): 213 - 223
    Cited by:  Papers (4)
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    Study of charge trapping and conduction in pure and iodine doped biaxially oriented polypropylene (BOPP) is presented. Structural and chemical modifications induced by iodine were investigated using X-ray, optical and infrared methods. Optical spectra of doped BOPP show absorption at 290 nm from charge transfer complexes. X-ray examination revealed a decrease in crystallinity and crystallite size after doping. The effect of iodine on charge trapping was determined by thermally stimulated current technique. Deep traps (120°C peak) at crystalline-amorphous interfaces are destroyed by iodine, which provides new traps (68°C peak) with activation energy 0.9 eV. Pressure dependence of conductivity indicates ionic conduction in pure samples and electronic conduction in doped samples. Steady state currents in 0.5%wt iodine doped BOPP were measured for fields 1 to 5×105 V cm-1 and at elevated temperatures 22 to 50°C. Iodine enhances conductivity by ~700× in pure BOPP and the steady state conductivity shows a good fit of the 3-D Poole-Frenkel theory to the experiment. It is proposed that trapped electrons (arising due to donor-acceptor action) thermally released through PF lowering, predominantly contribute to the conduction View full abstract»

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  • Electric field calculation for an axially-symmetric insulator with surface contamination

    Publication Year: 1994 , Page(s): 332 - 339
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (448 KB)  

    The classical method of integral equations was applied to determine the electrostatic field distribution on an insulator coated with a thin homogeneous surface layer. Results of calculations of the electric potential and the electric field on both uniformly and nonuniformly polluted model insulators coated with layers of different surface conductivities are presented in this paper. An application of this method to the determination of distribution of the electrostatic field on a polluted longrod insulator has been demonstrated View full abstract»

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  • Influence of sand/dust contamination on the breakdown of asymmetrical air gaps under switching impulses

    Publication Year: 1994 , Page(s): 305 - 314
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (676 KB)  

    This paper discusses the influence of airborne and surface-adhering sand/dust contamination on the breakdown characteristics of asymmetrical air gaps when subjected to standard switching impulses of both polarities. Extensive measurements of breakdown voltages and breakdown times are carried out under clean and polluted conditions using rod-plane and sphere-plane gaps. When positive switching impulses are applied to gaps ⩽1.8 m, the presence of sand/dust particles ⩽150 μm diameter and ⩽2 g/m3 concentrations have insignificant influence on the breakdown characteristics of the air gaps. However, the presence of such particles can greatly affect the breakdown characteristics for negative switching impulses. Under such conditions, the particles can decrease V50 by ⩽40% for gaps with field factor f ⩽3.5. For gaps with 3.5<f<12, the contamination can increase V50 by ⩽80%. For more nonuniform field gaps, V50 values for clean and contaminated conditions are similar. The particles can also significantly influence the breakdown time lag characteristics under negative switching impulses. The observed effects are primarily caused by sand/dust particles which settle on the cathode, while the particles present in the interelectrode gap or on the anode have very little influence View full abstract»

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  • The dielectric properties of meat

    Publication Year: 1994 , Page(s): 181 - 187
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (488 KB)  

    The permittivity and conductivity of beef and chicken samples were measured in the frequency range of 1 Hz to 1 MHz. Differences were observed in these dielectric spectra for commercially purchased, as compared to freshly slaughtered samples. In particular, fresh samples display a greater directional anisotropy in their electrical properties and a smaller, frequency-dependent conductivity. Changes in the dielectric properties are also produced by freezing and cooking procedures. These results indicate that measurement of the low-frequency dielectric properties of meat products could serve as a monitor of their storage and preparation history View full abstract»

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  • A study of dielectric relaxation in aluminosilicate-filled low-density polyethylene

    Publication Year: 1994 , Page(s): 169 - 180
    Cited by:  Papers (9)
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    Space charge formation in low-density polyethylene (LDPE) filled with zeolites and clays has been investigated by the thermally stimulated current method. The presence of fillers affects the dielectric properties due to additional dielectric relaxation phenomena, which depend on the structure of the inorganic filler. Pores or cages existing in the zeolite frame enable their compensated ions to move away from their neutral position under electric field to form dipoles of very low activation energy and high attempt-to-escape frequency. The activation energy is related to the pore sizes of zeolites. However, kaolin-based clay which has movable cations on its surfaces form an interfacial dipole between the LDPE and clay. A `Maxwell-Wagner' interfacial relaxation behavior was observed in the clay-filled LDPE system. The activation energy of interfacial relaxation of the clay-filled LDPE system is higher than that of dipole relaxation of the zeolite-filled LDPE View full abstract»

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  • Transform relationship between Kerr-effect optical phase shift and nonuniform electric field distributions

    Publication Year: 1994 , Page(s): 235 - 246
    Cited by:  Papers (27)
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    Electric field distributions measured using the Kerr effect cause a phase shift between light components polarized parallel and perpendicular to the electric field, proportional to the magnitude squared of the electric field components in the plane perpendicular to light propagation integrated over the light path length. One wishes to recover the electric field distribution from measurements of light phase shifts. For axisymmetric geometries where the electric field depends only on the radial coordinate and whose direction is constant along the light path, as is the case along a planar electrode, the total phase shift for light propagating at a constant distance from the center of symmetry and the electric field distribution are related by an Abel transform pair, a special case of Radon transforms typically used in image reconstructions with medical tomography and holography. The more general Radon transform relates the optical phase shift to non-axisymmetric electric field distributions but is restricted to cases where the applied electric field is perpendicular to the plane of light propagation. If the applied electric field direction changes along the light path, it becomes necessary to account for the change in direction of the light components parallel and perpendicular to the applied electric field and the light polarization equations are generalized View full abstract»

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  • Formulas to describe the bias and standard deviation of the ML-estimated Weibull shape parameter

    Publication Year: 1994 , Page(s): 247 - 253
    Cited by:  Papers (12)
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    The purpose of this paper is to present two formulas which can be used with the maximum likelihood method to estimate the Weibull shape parameter from uncensored data. The first formula unbiases the shape parameters for sample sizes of 3 and up. If this formula is added to the standard ML method, the bias is reduced to typically <0.3% (or even <0.05% depending on which set of test data is chosen) of the shape parameter value. The second formula gives the relative standard deviation of the shape parameter estimator with an error of typically <1%. Both formulas are derived from an assumed relationship between the sample size and the asymptotic behavior of a parameter under consideration. In addition, an unbiasing formula is given for the generalized ML method 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