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Electrical Insulation, IEEE Transactions on

Issue 3 • Date June 1985

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Displaying Results 1 - 25 of 34
  • Table of contents

    Page(s): c1
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    Freely Available from IEEE
  • IEEE Electrical Insulation Society

    Page(s): c2
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    Freely Available from IEEE
  • Secondary Electron Emission from a Charged Dielectric

    Page(s): 485 - 491
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    Charges on the surface of fluorinated-ethylene-propylene affect its secondary electron emission coefficient. Measurements with impact energies exceeding that energy which causes peak emission have been made in regions where the local electric field produced by the surface charge is normal to the surface and in regions where it is oblique. The surface of the 6-mm wide specimen was charged to either 6 or 10 kV. Because the impinging primary beam was deflected by the charged specimen, numerical modeling was used to predict the beam's impact energy E, impact angle ¿, and the impact point. The formula (E0/E) ncos¿ predicts the coefficient in the region of normal field up to 60° although E0 depends upon the electric field and also on the history of the specimen. Near the edges where the field is obliquie, the measured coefficient departs significantly from what the formula predicts. View full abstract»

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  • Electrification Phenomena on Insulating Materials in an Ion Flow Field

    Page(s): 493 - 498
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    Many researchiers have investigated electrical environmental problems under HV transmission lines. Electrification of an object is one of the important factors in the case of dc transmission lines. In this research, electrification of the surface of an insulating material (50 cm square and 5 mm thick PMMA plate) by an ion flow was studied. A rod-plane electrode gap was used to supply the ion flow, and the charge accumulated on the sample surface was measured. From the measurement, the surface potential was evaluated to be about 20 kV maximum for the experimental conditions. Additionally, an unexpected phenomenon was observed. An abnormal decrease of the charge was observed after the removal of the applied potential for the ion supply when the charge on the surface exceeded 70 ¿C/m2. The distribution of charge density was mapped with the use of an electrometer. The distribution was also visualized by sprinkling electrified powder on the surface. The process of this phenomenon is discussed in this-work and the following conclusions are obtained. The phenomenon of decreasing charge is believed to be caused by the fall of ions of opposite polarity and the fall of small neutral particles onto the sample surface. The contour line was observed in the visualized pattern but there was no abrupt variation in the charge density distribution. View full abstract»

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  • Charge Simulation Modelling of Three-Core Belted Cables

    Page(s): 499 - 503
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    A charge simulation method is used to represent sheathed, three-core, belted cables having circular conductors. Each conductor is represented by Nc infinite line charges arranged in a circular pattern inside the conductor. The sheath is represented by Ns infinite line charges arranged in a circular pattern, outside the sheath. It is shown that if the total number of representative charges is in the range of 60 to 80, a very accurate simulation is achieved. For best overall accuracy, the Ns/Nc ratio should be kept in the range of 1.5 to 2.1. Under such conditions, the percentage potential error is normally below 0.2% whereas the field deviation angle is less than 0.3 degrees. View full abstract»

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  • The Effect of Doping on the Voltage Holdoff Performance of Alumina Insulators in Vacuum

    Page(s): 505 - 509
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    Alumina ceramics doped with various combinations of Cr, Mn, and Ti were fabricated into hollow cylindrical insulators, then assembled into vacuum diodes and tested with 25 ¿s voltage pulses. Four doped alumina ceramics with total dopant levels of 2.6 to 4.7% wt and partial Cr plus Ti dopant levels of 1.0 to 2.4% performed very well. They had voltage holdoffs significantly better (25 to 40%) than plain alumina ceramics. Ceramics with total dopant levels of 5.3 to 5.6% performed only slightly better than plain alumina. Ceramics with partial Cr plus Ti dopant levels of 3.8 to 4.0% had significantly improved voltage holdoff capabilities, but undesirably high permanent failure rates (19 to 33%). Ceramics with total dopant levels greater than 7% performed very poorly, nearly all suffered permanent damage from breakdowns. These results suggest that desirable upper limits for doping are 5% for total dopants and 3% for Cr and Ti combined. Thus, doping a 94% Al203 alumina ceramic with appropriate amounts of Cr, Mn, and Ti can significantly improve the voltage holdoff capability, of insulators fabricated from such ceramics. These doped ceramic insulators are suitable for use in ultrahigh vacuum applications. View full abstract»

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  • Improved Potential Grading Methods with Silicon Carbide Paints for High Voltage Coils

    Page(s): 511 - 517
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    This paper presents surface potentials and the accompanying thermal analysis on, two improved potential grading methods with silicon carbide (SiC) paints for HV generator coils: (1) double-coating of SiC layers along a coil and (2) combination of a conducting intersheath and a SiC paint. Approximate equations describing the thermal behavior for both methods are derived on the assumption of ideal nonlinear conductivity. The double-coating method shows effective regulation of local heating, though total heating is not suppressed. A simplified model of the combination method predicts a remarkable heat suppression effect, which also is verified with numerical calculation. View full abstract»

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  • A Probabilistic Insulation Life Model for Combined Thermal-Electrical Srresses

    Page(s): 519 - 522
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    The Weibull distribution is widely used in statistical problems related to aging of solid insulating materials subjected to electrical stress. The main object of this paper is to explain the Weibull probability function in such a way that it can be applied to the statistical analysis of the risk of failure for solid insulating materials or structures subjected to single or combined (in particular thermal-electrical) stress situations. For this purpose, appropriate expressions for the scale and shape parameters of the two-parameter Weibull function are proposed, starting from a model for combined-life, based on the inverse power model for electrical life and the Arrhenius relationship for thermal life. The agreement of the statistical model thus obtained has been verified by means of experimental tests carried out on Low-Density Polyethylene. View full abstract»

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  • Life Characteristics of Medium Size Insulated Wire Subjected to Short Time, High Current Faults

    Page(s): 523 - 528
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    This paper continues the study of damage done to insulated wire by high currents which occur during the brief time necessary for protective devices to clear a bolted short circuit. The damage was measured by the decrease in dielectric strength related to various values of the time integral of the square of the current. This is called I2t. One major advantage of this approach is the definiteness with which significant damage is identified. The data reported here when combined with the data of the previous paper shows a linear relationship between the logarithm of I2t and cross sections of the most used building wires. View full abstract»

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  • Reduction of Surface Charge-Induced Electric Field Enhancement and Increase in AC Surface Flashover Voltage

    Page(s): 529 - 536
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    Surfactant is painted partially on a cylindrical insulator having a "back-side" (Inner) electrode, to change the distribution of the accumulating surface charge (residual charge) generated by ac partial discharge. The surfactants used are Neogen T®, Catiogen L®, or Tween 20®; the insulating material is polyvinyl-chloride heat shrinkable tube. Ac flashover voltage in air (ACFOV) depends on the surfactant applied: ACFOV decreases in the order Neogen>Catiogen¿non-painted¿ Tween; ACFOV of the Neogen-painted insulator is about 1.4 times higher than that of the Catiogen-painted one at an electrode distance of 140 mm, though the painted part of the two specimens has the same conductivity. The measured distribution of the accumulating charge differs between the Neogen-painted and the other specimens, though the maximum charge density on the surface does not differ much. These experimental results cannot be explained sufficiently by the decrease in the static electric field that is due to the increase in surface conductivity of the painted part. The calculation of the electric field enhancement due to the accumulating charge shows that the field near the electrode edge with the Neogen is lower than that for the other specimens. The higher ACFOV of the Neogen-painted insulator may be caused, not by increasing the surface conductivity, but by the decrease in the field enhancement on account of the difference in the distribution of the accumulating charge. View full abstract»

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  • The Use of Copper Electrodes for the Comparative Tracking Index Test

    Page(s): 537 - 542
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    If failure of electrical insulation occurs after a product has been in service for a considerable time, the mechanism involved is usually that of a carbonaceous track which develops between electrodes under conditions of intermittant moisture. A number associated with specific insulations and designed to rank insulations in order of their ability to avoid tracking is known as the comparative tracking index (CTI). There is little doubt as to the importance of the test that establishes the CTI value but there is much concern about its accuracy. This paper proposes modifications of the test equipment in an attempt to make the test more closely represent the conditions in the field and to make determination of the CTI value less subject to individual interpretation of the data. The proposed changes have been tested by laboratories in this country and Europe. View full abstract»

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  • Thermal Shocks Due to Repeated Moderate Arcing on Line Insulators

    Page(s): 543 - 548
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    Thermal shocks on line insulators produced by arcs, which may be intentionally repeated due to reclosing, or randomly caused by arc-backs etc., are investigated. A quantitative analysis of this phenomenon has been developed. The total arc power at the arc-insulation interface required for the analysis has been estimated experimentally for currents up to 850 A. Arc power appears to be proportional to current. The approach adopted is identical for both fragile and elastic materials since the temperature is chosen to be at threshold. The consequences of surface arcing for a new insulator material can be predicted approximately, using the relationships presented in the paper. The heaviest thermal shock appears to be proportional to the square root of the number of arcings. A doubled reclosing can contribute between 25 and 50% increase in the thermal shock compared to that of a single arc. With moderate arcs, the effect of material properties on the temperature rise for single or multiple shocks is similar. It is recommended that the thermal shock due to repeated arc-back be calculated as an equivalent single arc with the time equal to the sum of all individual times. View full abstract»

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  • Silicone Elastomer Vulcanized by the Hydrosilation Reaction and its Influence on Properties of a Modified Mos Device

    Page(s): 549 - 555
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    A p-MOS device in which the gate position is incompletely covered by the gate electrode has been used as a test device to estimate influence of silicone elastomer on residual current after gate operation. The elastomer was vulcanized by the hydrosilation reaction. It was found that the residual current could be represented as a function of the hardness and electrical conductivity of the silicone elastomer; that is, the current increased with decreasing hardness and increasing conductivity over the temperature range from 100 to 150°C. Comparison of activation energies measured by the residual current and by electrical conductivity indicated that different mechanisms of charge transport may be in operation, The differences may be due to the presence of dipole moments such as from unreacted hydrosilyl groups and of certain species such as water and chloride ions. View full abstract»

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  • The Effect of the Polymer Coating on Residual Current of Mos Devices

    Page(s): 557 - 560
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    The influence of polyimides on seniconductor devices has been studied by measuring the residual current in an MOS test device in which the gate position was0 incompletely covered by the gate electrode. Residual currents were found to be a function of the heat-treatment temperature of the coated polyamic acid. At first the residual current decreased with increasing heat-treatment temperature, untill a minimum value was reached, then it increased with temperature. These phenomena are d'iscussed with respect to the physical and chemical properties of the polyimide, e. g. flowing temperature, adhesion characteristics, decomposition temperature, impurities, and amount of unreacted amidic acid groups. Unreacted amidic acid groups and decomposition of polyimide caused a high residual current, while good adhesion of the polyimide to the MOS device brought about a low residual current. View full abstract»

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  • The Effect of Absorbed Oxygen on Electrical Treeing in Polymers

    Page(s): 561 - 566
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    This paper describes the effect on electrical treeing of oxygen absorbed in physical spaces such as microvoids or free volume in polyethylene. The ac tree initiation and growth were investigated at room temperature using untreated samples and also samples degassed by a vacuum pump. The tree starting voltage of the degassed samples is much higher than that of untreated samples. The experimental results show that this improvement can be attributed to the removal of oxygen from PE. We also observed in detail the processes of tree initiation and growth in the degassed samples. The observations, with other results, led us to conclude that the charge carriers injected from the point electrode play a dominant role in the tree initiation. View full abstract»

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  • Some Dielectric and Mechanical Properties of Heat Treated Biaxially Drawn Pet Films

    Page(s): 567 - 573
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    The dc dielectric strength of heat-treated biaxially drawn polyethylene terephthalate (PET) is studied under mechanical stresses. The sample is prepared on films with a draw ratio of 3.3x3.9 obtained by a continuous process. To study the effect of crystallinity on the dielectric strength, the sample that is held to constant size is annealed for durations of 1 and 60 min in a silicone oil bath maintained at a fixed temperature within ±2°C. The annealing temperature range is from 100 to 2200C. The maximum dielectric strength of the sample under no mechanical stress is found to occur at an annealing temperature of about 1400C. But the compressive stress showing maximum dielectric strength under compressive stress increases with the annealing temperature, and its value is not significantly varied by the cooling process after annealing. Compared with undrawn and uniaxially drawn PET, the biaxially drawn sample has good mechanical properties and dielectric strength characteristics under mechanical stresses. However, it is believed that the best annealing condition should be decided by the requirements for the electrical and mechanical characters of the sample. View full abstract»

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  • Interface Traps and Swelling of Polypropylene Films Immersed in Silicone Oils

    Page(s): 575 - 580
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    Biaxially stretched PP (polypropylene) films immersed in silicone oil showed TSC peaks P1 and P2 due to ions trapped in the oil-PP interface region. Their peak temperatures were lowered by oil-PP interaction such as swelling. The equations governing the swelling of a crystalline polymer were deduced from the analogy of the swelling of a cross-linked polymer. The experimental values of the degree of swelling of PP films immersed in silicone oil agreed well with the theoretical ones calculated from the equations. TSC peak temperatures decreased with increasing degree of swelling of PP films. The good correlation between TSC and swelling gave evidence for the modification of surface traps by swelling. View full abstract»

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  • Electrical Breakdown of N20-SF6, N20-CCL2F2 and N2O-CO2 Gas Mixtures

    Page(s): 581 - 585
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    Using 112 mm diameter, Harrison profile stainless steel polsihed electrodes, uniform field dc breakdown voltages are measured for N2O mixtures with SF6, CCl2F2, and CO2 in the pressure range of 0.02 to 1 MPa and gap lengths up to 20 mm. The results show that the breakdown strength (E8/P) of SF6, CCl2F2 and their mixtures decreases with pressure while it remains practically constant for N2O and N2O-CO2 mixtures over the investigated pressure range. From the breakdown data, limiting sparkover strengths (E8/P)lim are calculated for various mixtures which are expressed by a general expression (E8/P)lim = A+B (X)C, where X is the percentage content of SF6 in SF6-N2O mixtures, CCl2F2 in CCl2F2-N2O mixtures, and N2O in N2O-CO2 mixtures. Values of constants A, B, and C are given for the investigated gas mixtures. View full abstract»

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  • A Modek for the Production of Initial Electrons by Detachment of SF-6-IONS

    Page(s): 587 - 594
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    Experiments with positive pulses in a sphere-to-plane gap give evidence of the fact that initial electrons are provided by collisional detachment of SF6 ions. The position-dependent density of negative ions prior to a pulse application is calculated numerically for different geometries. The results are then included in a quantitative model for the electron production rate which is based on physical assumptions about the detachment coefficient. From a comparison with the measurement, ¿/n is obtained as a function of E/Ecr. View full abstract»

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  • Ionization and Attachment Coefficients in Freon-12 and Co2 Gas Mixtures

    Page(s): 595 - 599
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    Uniform-field steady-state ionization growth currents are measured in CO2 and CCl2F2 + CO2 mixtures. Effective ionization, ionization and attachment coefficients are reported in the range of 2. lx10-15 ¿ E/N ¿ 5.4x10-15 V cm2. Experimental E/N limits are observed for several CO2 concentrations in the mixture, and also sparking potentials are measured as a function of Nd in the range of l.65x1017 ¿ Nd ¿ 1.97x108 cm-2 for these mixtures. View full abstract»

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  • Positive Corona Processes in Electronegative Gaseous Dielectrics

    Page(s): 601 - 607
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    Events occurring in a positive point/plane gap Subjected to quasi-step function voltages have been monitored by both terminal and optical measurements. Evidence is presented on the importance of the critical al initiation volume in the vicinity of the anode in determining both the time lag and the luminous extent of the corona. Changes in the corona characteristics are explained on the basis of spatial modifications of the ionization zone resulting from space charge distortion. An approximate theoretical basis for the results is explored in terms of the detachment of negative ions and illustrated with reference to seeding of the discharge with a low ionization potential additive. View full abstract»

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  • Drying Process of Insulating Materials of Transformers

    Page(s): 609 - 618
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    The insulating systems of transformers must be dried before impregnation with insulating oil. Some works dealing with the drying process of insulating materials have been published, however, practical methods to analyze the drying process have not. In order to develop a practical method, the drying process of transformer boards was investigated, and results obtained in this investigation were applied to analyze the drying process of transformers. At the beginning, changes in the water vapor pressure in the vacuum container due to the release of water vapor from transformer boards were measured during the drying process. Measured changes were then compared with calculated changes, based on the assumption that water vapor is released from insulating materials due to the difference of water vapor pressure. These results were applied to calculate the drying times of insulating systems in transformers. It was found that if the appropriate permeability of water vapor in insulating materials can be selected, the calculated drying process coincides with the measured drying process. View full abstract»

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  • Influence of Mica Tapr Application on Insulation Characteristice of High Voltage Rotating Machinery Coils

    Page(s): 619 - 624
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    This paper studies the influence of mica tape application methods on the insulation characteristics of HV rotating machinery coils generally. Resin impregnability , electrical failure properties and mechanical properties were tested on specimens prepared by sheets or tapes with different widths. From these test results, it was clarified that these insulation characteristics were influenced significantly by the mica tape application methods. This influence was caused by resin impregnating the interfaces between the mica tapes and thus weakening the resistance of the tape to electrical and mechanical stresses. View full abstract»

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  • Impregnation Study of Porous Elements of High-Voltage Components

    Page(s): 625 - 627
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    The impregnation of HV components is important if not critical for reliable operation. Fine windings, porous insulation such as kraft paper and pressboard, and similar elements need to be impregnated for good thermal conductivity, mechanical strength and, in the case of insulation, to minimize internal discharges. Although widely used, there appears to be little systematic work done to explain the important factors governing the basic process when a filled, thermosetting compound such as a filled epoxy is used in a pressure impregnation. In this paper we have derived an expression for the depth of penetration of a thermosetting compound into a porous substrate such as kraft pressboard. The equation is extended to the case of a filled thermoset where filtration of the filler occurs at the substrate surface. The expression derived relates filter cake permeability, substrate permeability, applied pressure and the viscosity-time relationship of the impregnating. filtered compound. Data are presented showing good agreement with the derived expression. View full abstract»

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  • Physical Behavior of Paraffinic Oils at Low Temperatures

    Page(s): 629 - 638
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    This paper presents a study and an analysis of the low-temperature physical properties of a paraffinic oil refined from Canadian feedstock. The study demonstrates that a significant attribute of this oil is the mechanism of wax formation below the cloud point, This wax formation can explain the higher low temperature viscosity of the oil as compared to that of a naphthenic oil, its non-Newtonian behavior, and a critical temperature zone where the oil gels. Finally , DSC analysis was found successful to analyze this wax formation. View full abstract»

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Aims & Scope

This Transactions ceased production in 1993. The current retitled publication is  IEEE Transactions on Dielectrics and Electrical Insulation.

Full Aims & Scope