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Electrical Insulation, IEEE Transactions on

Issue 3 • Date June 1991

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Displaying Results 1 - 25 of 25
  • Comments on "The temperature dependence of homogeneous field breakdown in synthetic air" by W.S. Zaengl et al

    Publication Year: 1991
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (104 KB)  

    For original paper see ibid., vol.26, no.3, p.380-90 (1991). In the above-named paper the unit Townsend (Td) is used when referring to gaseous collision parameters. With reference to electrical insulation, it may be argued that, on grounds of its magnitude, the Townsend is an impractical unit.<> View full abstract»

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  • Discussion: partial discharges in ellipsoidal and spheroidal voids

    Publication Year: 1991 , Page(s): 537 - 539
    Cited by:  Papers (2)
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    Some questions are raised regarding the model described by Crichton et al. (see ibid. vol.24, p.335-342, 1989) in which the entire volume of the void is considered to be involved in the discharge process. The commenter questions how it can be explained that an increase in the applied voltage results in an increase in the discharge magnitude. In response it is noted that the assumption was made to allow evaluation of the change in the void dipole moment. This assumption is open to criticism with respect to discharge development, but is is maintained that this does not necessarily imply that, with reference to the actual dipole moment magnitude, the assumption is unsound. To assess the validity of the assumption in this context, it is necessary to compare the dipole moments associated with other charge patterns.<> View full abstract»

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  • A question in electromagnetic theory

    Publication Year: 1991 , Page(s): 510 - 512
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    Electromagnetic theory formulations may be stated with or without surfaces of discontinuity. The latter approach is simpler in many respects, but it presents some difficulties if the realization of no time dependence is to be considered. This dilemma arises in electrical insulation studies in which interfaces between media are present. The author examines two mathematically simple cases in order to elucidate this choice between two descriptions View full abstract»

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  • Field behaviour at a triple junction in composite dielectric arrangements

    Publication Year: 1991 , Page(s): 500 - 509
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (548 KB)  

    The author examines the field behaviour at and near various points of contact between a solid dielectric and a conductor. The topics discussed include analytical expressions and numerically calculated results of field strength as well as their potential practical applications. The effect of conductivity is explained in some cases. There are principally three contact conditions depending on the contact angle; 90, 0 to 90, and 0°. The contact angle between 0 and 90° results in a field concentration of K×lm near a contact point where l is the distance from the point. In the case of zero contact angle, where a solid dielectric and a conductor are both rounded or planar, a simple mathematical function expresses the effect of relative permittivity on the field concentration at the contact View full abstract»

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  • Charge accumulation on insulating spacers for HVDC GIS

    Publication Year: 1991 , Page(s): 418 - 427
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (812 KB)  

    A capacitive probe measurement that can be used to quantify the charge density on solid insulators is introduced. Studies performed in the development of a ±125 kV high-voltage DC (HVDC) gas-insulated converter station and ± 500 kV HVDC switchgear (HVDC-GIS) are reviewed. The properties and mechanisms of surface charging, the optimum design of the spacer and its breakdown characteristics are summarized. Problems associated with capacitive probe measurement of surface charge and a practical solution to obtain the charge distribution on the spacer are presented View full abstract»

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  • Illusory Paschen curves associated with strongly electronegative gases

    Publication Year: 1991 , Page(s): 391 - 397
    Cited by:  Papers (6)
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    Using analytical linear regression analysis, it is shown that, for a strongly electronegative gas, the (direct) breakdown voltage curve obtained with a moderately nonuniform field is effectively linear. For a strongly electronegative gas, breakdown voltage measurements made on a moderately nonuniform field test gap give rise to an apparently liner curve. The curve can be designated a Paschen curve, but the erroneous nature of this designation becomes apparent from a linear regression analysis of the experimental breakdown data View full abstract»

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  • Surface charging and flashover of spacers in SF6 under impulse voltages

    Publication Year: 1991 , Page(s): 428 - 442
    Cited by:  Papers (11)
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    The authors describe a series of experiments to study prebreakdown spacer charging and subsequent flashover in a compressed gas insulated rod-spacer-plane system under positive impulse voltages. Prebreakdown corona is identified as the most likely source for spacer charging. Surface charges were measured in situ with capacitive probes after the applied lightning impulse voltage had decayed to zero. Numerical computation of resultant electric fields, using the surface charge simulation method, shows that the electric field due to surface charges significantly lowers the electric field near the rod electrode but enhances the overall electric field over the rest of the spacer surface. The flashover voltage with a spacer is higher than for a rod-plane gap. A reversal of the applied impulse polarity may lower the flashover voltage for a rod-spacer-plane gap View full abstract»

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  • SF6 insulation and its application to HV equipment

    Publication Year: 1991 , Page(s): 358 - 366
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (748 KB)  

    Very fast transient overvoltage (VFTO) problems and studies on SF 6 insulation are outlined, and trends in gas-insulated equipment design are discussed. The discussion covers recent topics on development and typical products, including 550 to 800 kV gas-insulated switchgears (GISs) and 275 kV gas-insulated transformers. The authors deal with insulation in nonuniform electric fields View full abstract»

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  • Optimum electrical PD test method for large capacitors

    Publication Year: 1991 , Page(s): 479 - 486
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (596 KB)  

    The optimum method for electrical partial discharge testing of large capacitors, including the effects of internal inductance, is determined. The results indicate that internal inductance does not adversely affect detection sensitivity if the detection impedance is made equal to the critical damping resistance. This has the advantage of providing a nonresonant waveform which can be detected in a near-optimum manner using a simple low-pass filter View full abstract»

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  • Computer-aided impulse-voltage testing

    Publication Year: 1991 , Page(s): 344 - 348
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (416 KB)  

    The automation of impulse voltage tests by a control and measuring system based on computers (computer-aided control and measurement system) offers new possibilities for high-voltage (HV) research and quality inspection. An industrially manufactured computer-aided control and measurement system is presented. Its hardware is characterized by a master computer for data input, operation, and data processing, and a slave computer for all fast control processes. It can be extended by a digital voltage/time measuring system. The computer-aided control and measurement system is well protected against interference by protective circuits, optical links, and electromagnetic shielding. The software comprises the automatic control and supervision of the generator, programs for all typical impulse voltage tests, evaluation of the voltage parameters, statistical processing of the measured data and printing of the test record View full abstract»

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  • Effect of surface charge on impulse flashover of insulators in SF 6

    Publication Year: 1991 , Page(s): 443 - 452
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (656 KB)  

    The effect of surface charge on the impulse flashover of short spacers in SF6 was investigated. A split-electrode arrangement allowed scanning of the entire space surface by a capacitive probe. With a heterocharge distribution which facilitates both inception and propagation of the discharge, the flashover level is reduced by as much as 50% for sinusoidally distributed charge of peak density 40 μC/m2. With monopolar charge, only positive charge near the cathode has any significant effect on breakdown, the reduction in impulse strength being ~35% at 40 μC/m2. Tests with metal insets show that although the shielding effect is reduced in the presence of heterocharge the impulse strength of spacers with insets is still superior to that of plain spacers for the same charge density. The possible effects of surface charge on flashover of longer spacers is discussed in terms of a transition from a streamer to a leader type of breakdown mechanism View full abstract»

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  • Influence of a dielectric barrier on the stochastic behaviour of Trichel-pulse corona

    Publication Year: 1991 , Page(s): 405 - 415
    Cited by:  Papers (14)
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    The influence of a solid polytetrafluorethylene (PTFE) dielectric barrier on the stochastic behaviour of negative (Trichel) pulse corona discharges in air is examined. This behavior is revealed from measurement of conditional and unconditional corona pulse-amplitude and pulse-time--separation distributions. The results indicate that the presence of a dielectric surface on the anode effectively reduces the electric field at the point electrode, but does not affect the occurrence of Trichel pulses, provided the point-to-plane gap spacing is greater than a critical value dc which depends on the area of the dielectric and the applied voltage. As the gap spacing approaches dc, the effect of dielectric-surface charging by the corona introduces measurable memory effects indicated by correlations between pulse amplitude and time separation from the previous pulse. For spacings less than dc, detachable corona-pulse activity is quenched by the presence of a quasi-permanent surface charge on the dielectric View full abstract»

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  • Modulation of partial discharge activity in GIS insulators by X-ray irradiation

    Publication Year: 1991 , Page(s): 460 - 468
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (704 KB)  

    A system was assembled which can perform high-sensitivity partial discharge (PD) measurements under combined electric stress and X-ray irradiation on 138-kV class gas-insulated switchgear (GIS) post insulators. Under X-ray irradiation, the PD pulse repetition rate is increased and the discharge inception voltage (DIV) is sharply reduced. The DIV of these insulators under X-ray irradiation was recorded at values at low as 25 kV, although some samples could not be brought into discharge at 400 kV without X-rays. The modulation effect of X-rays on PD activity permits the location of the discharge side. In general, pulse-height and pulse-phase patterns are more tightly clustered with X-ray irradiation, but the patterns display a board range of features depending on the type of defect, voltage, and time on voltage View full abstract»

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  • On the assessment of extremely low breakdown probabilities by an inverse sampling procedure [gaseous insulation]

    Publication Year: 1991 , Page(s): 367 - 377
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (628 KB)  

    First breakdown voltages obtained under the inverse sampling procedure assuming a double exponential flashover probability function are discussed. An inverse sampling procedure commences the voltage application at a very low level, followed by applications at stepwise increased levels until a breakdown occurs. Following a breakdown, the procedure is restarted at the initial level. The procedure is repeated until a predetermined number of breakdowns have occurred, and the average and standard deviation of the observed first breakdown levels are recorded. The authors derive the relation between the flashover probability function and the corresponding distribution of first breakdown voltages under the inverse sampling procedure, and show how this relation may be utilized to assess the single-shot flashover probability corresponding to the observed average first breakdown voltage. Since the procedure is based on voltage applications in the neighbourhood of the quantile under investigation, the procedure is found to be insensitive to the underlying distributional assumptions View full abstract»

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  • Electric field theory and the fallacy of void capacitance

    Publication Year: 1991 , Page(s): 458 - 459
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (136 KB)  

    The concept of the capacitance of a gaseous void is discussed as applied to electrical insulation science. The most pertinent aspect of the capacitance definition is that of reference to a single-valued potential difference between surfaces. This implies that these surfaces must be surfaces of equipotential. With this essential characteristics the validity of void capacitance is examined View full abstract»

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  • The theory and measurement of partial discharge transients

    Publication Year: 1991 , Page(s): 487 - 497
    Cited by:  Papers (26)
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    A theoretical approach to partial discharge transients is presented. This approach is based on the relationship between the charge induced on the measurement electrode by those created in the interelectrode volume during partial discharge activity. The primary sources for these induced charges are the charges which, as a result of partial discharge activity, are distributed within the voids of the insulation medium. These charge relationships are derived, and their application to the measured transients associated with the time dependence of the induced charge is presented. The application to multiple electrode systems of practical interest is illustrated. A discussion of the salient features and practical aspects of the theory is included View full abstract»

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  • Theory of positive onset corona pulses in SF6

    Publication Year: 1991 , Page(s): 398 - 404
    Cited by:  Papers (14)
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    The mechanism of formation of positive corona onset pulses in SF 6 at 100 kPa is examined. A constant positive voltage of 50 kV is applied to an 0.5-cm diameter sphere located 6.5 cm from a grounded plane. The calculated current pulse has a width at half maximum amplitude of ~0.3 ns, thus explaining the origin of subnanosecond current pulses in SF6. During the current pulse a streamer moves out into the gap along a 100-μm channel, with the electric field in the streamer trail E>E*, where E* is the critical field for which ionization equals attachment View full abstract»

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  • Comparative analysis of methods for computing 2-D and 3-D electric fields

    Publication Year: 1991 , Page(s): 529 - 536
    Cited by:  Papers (15)
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    On the basis of four high-voltage (HV) examples, electrical field calculations were performed using different computational methods. Three examples represent axisymmetric arrangements, one example is three-dimensional. The computations were performed using a boundary element program from the University of Sarajevo, a program based on the charge simulation method, developed at the Technical University of Munich, and the commercial finite element program ANSYS View full abstract»

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  • The temperature dependence of homogeneous field breakdown in synthetic air

    Publication Year: 1991 , Page(s): 380 - 390
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (820 KB)  

    The time-resolved Townsend method is used to measure, among other parameters, the effective coefficient of ionization of α¯/N as a function of E/N in synthetic air (80% N2 , 20% O2 by volume) within a temperature range of ~27 to 124°C, where N is the gas number density, and E the electric field strength. Results show that effective ionization coefficients are lower for higher temperatures, thus leading one to infer that breakdown voltages should increase with temperature for constant values of the product Nd, where d is the gap distance. However, systematic breakdown voltage measurements in nearly homogeneous field conditions, did not support this temperature dependence. For room temperature, however, both measurements supported the well-known streamer breakdown theory View full abstract»

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  • Study of power coil resonance phenomena based on traveling wave theory

    Publication Year: 1991 , Page(s): 349 - 357
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (732 KB)  

    New measurement capabilities allow greater in-depth investigations of the propagation of guided electromagnetic waves inside a coil. Based on numerous measurements of the frequency-dependent conductance and susceptance of various arrangements of cylindrical and disc-type single-layer air-core coils, resonance phenomena of such arrangements, and the main influencing factors, are investigated. The results show dependencies which can be quantified by the application of the theory of traveling waves to the propagation of guided waves in coils. A single method, which is based on the interpretation of real physical phenomena, enables the prediction of the resonance frequencies of all orders View full abstract»

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  • A continuous UHF monitor for gas-insulated substations

    Publication Year: 1991 , Page(s): 469 - 478
    Cited by:  Papers (40)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (664 KB)  

    Assessing the condition of a GIS by measuring the UHF signals generated in it by partial discharges gives warning of developing faults. The signals are taken from couplers built into the equipment. The couplers are continuously monitored using special amplifying and detection units connected in a digital optical fiber network. The data collected can also be interpreted by an expert system and an analysis of the situation sent via a modem link to a PC. Laboratory trials of the continuous monitor have been carried out on a test rig of 400-kV GIS chambers. The basic principles of the monitor and the results of its trials are given View full abstract»

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  • Surface current density K: an introduction

    Publication Year: 1991 , Page(s): 416 - 417
    Cited by:  Papers (2)
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    The author discusses the vector surface of current density K used in electrical insulation studies. K is related to the vector tangential electric field Kt at the surface of a body by the vector equation KE t where Γ represents the surface conductivity. The author derives a surface continuity equation that represents the boundary condition which the potential distributions in the adjoining media must fulfill. The volume current may be small in comparison to the surface current, and consequently in deriving the potential solutions the first term in this equation can sometimes be neglected View full abstract»

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  • Analysis of the temporal electric fields in lossy dielectric media

    Publication Year: 1991 , Page(s): 513 - 528
    Cited by:  Papers (10)
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    The time-dependent electric fields associated with lossy dielectric media are examined. The analysis illustrates that, with respect to the basic time constant, these lossy media can take a considerable time to attain a steady-state condition. Time-dependent field enhancement factors are considered, and inherent surface-charge densities quantified. The calculation of electrostatic forces on a free, lossy dielectric particle is illustrated. An extension to the basic analysis demonstrates that, on reversal of polarity, the resultant tangential field at the interface could play a decisive role in the insulation integrity of a system View full abstract»

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  • PD phenomena on dielectric surfaces under DC stresses influenced by air humidity

    Publication Year: 1991 , Page(s): 453 - 457
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    Based on fundamental investigations of the charge accumulation on the surface of dielectric materials relevant for DC test equipment, it was found that partial discharge (PD) phenomena under DC stresses are affected by both local and remote charge generation. With increasing air humidity both charge generation processes are intensified, resulting in an unexpectedly strong reduction of the PD inception voltage. It is therefore concluded that DC test equipment for operating voltages ≳100 kV working in atmospheric air cannot be designed fully PD free at reasonable cost View full abstract»

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  • On exponential growth [of gas breakdown]

    Publication Year: 1991 , Page(s): 378 - 379
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (96 KB)  

    The agreement obtained between measured breakdown voltages and predicted breakdown values is frequently used as a means of assessing the validity of the theory/model in question. However, owing to the mathematical nature of exponential growth, it is easy to formulate a criterion that provides acceptable breakdown values, although the criterion may contain totally unrealistic features. An example from the work of A. Pedersen (1989) showing unrestricted exponential growth in SF 6 is used to highlight the insensitivity of breakdown voltages with respect to modeling 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