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Dielectrics and Electrical Insulation, IEEE Transactions on

Issue 1 • Date Feb 1997

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Displaying Results 1 - 20 of 20
  • Sudden flashover of nonceramic insulators in artificial contamination tests

    Publication Year: 1997 , Page(s): 79 - 87
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (904 KB)  

    This paper presents experimental and theoretical results to explain the phenomenon of sudden flashover on artificially contaminated nonceramic insulators. A sudden flashover in this paper is defined as a flashover occurring on a partially contaminated insulator, and which is preceded by little or no surface discharge activity. Sudden flashovers could occur in the field on those insulators where the wet surface resistance varies over a wide range along the insulator length. The mechanism of sudden flashover is significantly different from conventional contamination flashover that occurs in standard contamination tests. The insulators evaluated had weathersheds made from silicone and ethylene propylene diene monomer (EPDM) rubbers. The impact of the present study from the point of view of weathershed material, insulator design, development of a comprehensive laboratory test and field monitoring for evaluating the performance of nonceramic insulators in service are discussed View full abstract»

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  • Breakdown mechanism of liquid nitrogen viewed from area and volume effects

    Publication Year: 1997 , Page(s): 127 - 134
    Cited by:  Papers (23)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (668 KB)  

    We investigated the area and volume effects on the breakdown strength in liquid nitrogen (LN2) to discuss the breakdown mechanism in cryogenic liquids for superconducting power apparatus. We measured breakdown voltages in LN2 with and without thermal bubbles over a very wide range of the electrode size. Experimental results revealed that the breakdown mechanism changed from an area dominant to volume effective region at larger electrode configurations in LN2. Moreover, we discussed the contribution rate of area and volume effects to the breakdown strength in LN2. It was suggested that a mutual contribution of area and volume effects appeared in breakdown characteristics in LN2 under thermal bubble conditions, as a phenomenon peculiar to cryogenic liquids. Consequently, we pointed out that it is very important to consider both thermal bubbles and electrode surface condition for HV insulation of superconducting power apparatus View full abstract»

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  • Estimation of dc breakdown mechanisms in air gaps containing floating metallic particles

    Publication Year: 1997 , Page(s): 92 - 101
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (936 KB)  

    The characteristics of breakdown voltages against the position of floating metallic particles in atmospheric air are investigated experimentally. The breakdown mechanism is estimated on the basis of electric field calculation and visual observation of discharges at different voltages and a set of flow charts for calculation of breakdown voltage is proposed. The studied gaps are needle-to-plane and sphere-to-sphere electrodes of 120 mm in length forming Poissonian and Laplacian fields respectively and the shape of tested floating objects is a needle or sphere. The theoretical breakdown voltages obtained by the flow charts agree reasonably with the experimental ones View full abstract»

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  • Dielectric strength of SF6 insulation in EHV disconnectors

    Publication Year: 1997 , Page(s): 102 - 107
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (524 KB)  

    A new method for the calculation of parameters of SF6 insulation for extra HV GIS disconnectors is given. This method is based on a new criterion for leader inception, which is connected with the value of the peripheral electric field near the boundary of the streamer zone. The presence of such a critical field is confirmed by analysis of experimental results and physical considerations View full abstract»

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  • High-field single electron emission rates and their influence on the Paschen characteristics in compressed gases

    Publication Year: 1997 , Page(s): 135 - 145
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (936 KB)  

    By means of a newly developed statistical avalanche counting technique which enables high-field, single electron emission rates (SEERS) to be measured from unsparked freshly prepared surfaces having various thicknesses of oxide film, it is established for the first time that SEERS increases, for a given electric field, with an increase in the bulk modulus (hardness) of the material cathodes; also remarkably the thicker the oxide layer, the higher the SEERS. These trends are reflected in the Paschen sparking characteristics which show that the gaseous electric strength decreases with increase in the bulk modulus and increase of oxide layer thickness of the cathode material; and thus the increase in SEERS. This former trend is opposite to that established more than forty years ago. Other hitherto unobserved phenomena like a gas pressure effect, switching from a low to a high electron emission mode and vice versa, the influence of deliberate sparking and the total absence of spark conditioning are reported. Analysis of SEERS by the more successful Richardson-Schottky rather than the Fowler-Nordheim equation shows that the low electric field intensification factors derived increase with the bulk modulus of the cathode material and ultimately are determined by the polishing procedure View full abstract»

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  • The impulse breakdown trajectory in air between rod and plane electrodes

    Publication Year: 1997 , Page(s): 108 - 113
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (452 KB)  

    Image processing was used to analyze video recordings of electrical breakdown paths in a rod/plane electrode air gap. The number of segments in the breakdown path was found to vary as the applied over-voltage was changed. The results are discussed in terms of a prebreakdown space charge model View full abstract»

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  • PD source identification with novel discharge parameters using counterpropagation neural networks

    Publication Year: 1997 , Page(s): 17 - 32
    Cited by:  Papers (22)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1672 KB)  

    Computer aided partial discharge (PD) source identification using different multidimensional discharge patterns is widely regarded as an important tool for insulation diagnosis. In this paper, a neural network (NN) approach to PD pattern classification is presented. The approach is based on applying variants of the counterpropagation NN architecture to the classification of PD patterns. These patterns are derived from physically related discharge parameters, different from those commonly used. It is shown that considerable improvements of the classification quality can be obtained when an extended counterpropagation network with a dynamically changing network topology is applied to patterns that employ the voltage difference between consecutive pulses instead of the phase of occurrence as the main discharge parameter. Furthermore, using a particular parameter vector that takes the correlation between consecutive discharges into account also allows to solve the rejection problem with this type of NN View full abstract»

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  • Optical monitor for contamination on HV insulator surfaces

    Publication Year: 1997 , Page(s): 33 - 38
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (608 KB)  

    Ellipsometry is used to monitor naturally deposited contamination films on HV electrical power insulators that are used in overhead transmission lines and substations. Good correlation is found between the conventional ESDD (equivalent salt deposit density) method of measuring contamination and an ellipsometrically determined optical thickness of that contamination. The technique relies completely on the state of polarization of light reflected from the surface of a ZnSe witness piece which is placed on or close to the power insulator. Such a technique results in the thickness and refractive index of the deposited contaminant. The severity of contamination is then known by the value of the measured film thickness. Three patches of witness pieces were placed in the Labarre substation in New Orleans, LA. Comparison between conventional ESDD and ellipsometric measurements showed good agreement View full abstract»

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  • Surface flashover characteristics of diamond-like carbon thin films in vacuum

    Publication Year: 1997 , Page(s): 71 - 78
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (868 KB)  

    Synthetic thin films such as diamond-like carbon (DLC) and polycrystalline diamond thin films can be used to increase surface flashover voltage of dielectric materials used in HV devices operating in vacuum. This work presents experimental results identifying some surface flashover characteristics of diamond-like carbon (DLC) thin films in space vacuum conditions. The DLC samples used in the experiments are produced by a microwave plasma deposition technique. The electrode material was copper, and a dc voltage was applied between the electrodes. Surface flashover voltage characteristics and the breakdown voltage wave forms of DLC thin film samples were determined. The results showed that DLC thin films may not be suitable materials for HV applications as dielectric materials in vacuum when coated onto semiconductor materials. Additionally, these results were compared with the surface flashover characteristics of polycrystalline diamond thin film and quartz samples View full abstract»

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  • Space charge behavior under ac voltage in water-treed PE observed by the PEA method

    Publication Year: 1997 , Page(s): 52 - 57
    Cited by:  Papers (32)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (520 KB)  

    The pulsed electroacoustic method (PEA) has been applied to observe space charge formation under ac application (7 kVpk, 50, 0.1 and 0.001 Hz) in water-treed polyethylene samples in order to understand the degradation mechanism of water trees. A system with phase-resolving capability has been developed to measure the space charge distribution at any phase angle of the applied ac voltage. By comparing the observed charge distributions with theoretically predicted ones, it has been shown that the interfacial polarization due to the difference in conductivity between the treed and the regions without trees dominate the space charge behavior. It has become clear that the PEA method can be a powerful nondestructive method for evaluating water tree length View full abstract»

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  • Activity of moving metallic particles in prebreakdown state in GIS

    Publication Year: 1997 , Page(s): 39 - 43
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    The paper presents experimental results of measurements of prebreakdown activity, caused by free metallic particles in GIS, obtained using a phase resolved partial discharge (PRPD) analysis and acoustical measurements. The numerous parameters characterizing prebreakdown activity of particles were identified and analyzed. These included phase resolved distribution of charge, maximum charge, average charge per period, or per pulse, a balance of charge in positive and negative half-wave of voltage, pulse rate (number of pulses per period) for electrical and acoustic methods. The measurements were conducted in a compartment of real GIS, and Al as well as Cu particles of different shapes were investigated. The pressure varied from 150 to 550 kPa, however most measurements were taken at 450 kPa. A discharge model which takes into account the effect of a free metallic particle in GIS is presented View full abstract»

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  • Charge behavior in polyethylene-ionomer blends

    Publication Year: 1997 , Page(s): 58 - 63
    Cited by:  Papers (2)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (552 KB)  

    In order to explain a decrease of thermally stimulated current (TSC) at high poling fields, the behavior of space charge in two types of polyethylene (PE)/ionomer blends, PE/Surlyn 1652 and PE/Surlyn 1601, has been investigated by measuring the charge distributions and conduction characteristics. PE/Surlyn 1601 blends showed smaller current densities at high electric fields than PE/Surlyn 1652 blends. A considerable amount of negative charge was found to migrate into the bulk region of PE/Surlyn 1601 blends upon discharging, which was attributed to the strong electron affinity of ionic clusters existing only in Surlyn 1601. This migration of charge made the charge distribution uniform, resulting in a decrease of TSC at high poling fields. This phenomenon was not found in PE/Surlyn 1652 blends View full abstract»

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  • Insulator size effect on electron-irradiated quartz

    Publication Year: 1997 , Page(s): 88 - 91
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    A time-resolved current experiment measuring separately the surface and bulk currents flowing through an insulating sample under electron beam irradiation employing a scanning electron microscope is performed to investigate charging and flashover phenomena. A set of metallic apertures of various values of radius are used to vary the area of the insulator. It is observed that the bulk current decreases monotonically with time until reaching a constant value, while the surface current exhibits two different trends: decreasing monotonically with time, and decreasing with time at first and then increasing. Such observations are related to the establishment of a dynamic equilibrium between electron trapping and detrapping, as well as the flashover behavior, and depends on the insulator size and the experimental conditions View full abstract»

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  • Dielectric breakdown of a residual SF6 plasma at 3000 K under diatomic equilibrium

    Publication Year: 1997 , Page(s): 114 - 119
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (548 KB)  

    A residual plasma at 3000 K and under diatomic equilibrium is left inside an axially blown gas blast SF6 circuit breaker after the thermal extinction of an arc. The breakdown of such a residual plasma depends on the electron generation and loss mechanisms. Altogether six ionization and chemical reactions relevant to the time scale of breakdown have been taken into account. It has been found that the critical field strength for breakdown is proportional to the pressure and is equal to 2.0 V/(m.Pa). This field strength is in agreement with the experimental results View full abstract»

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  • Solution of low frequency complex fields in polluted insulators by means of the finite element method

    Publication Year: 1997 , Page(s): 10 - 16
    Cited by:  Papers (9)
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    A method to calculate the low frequency complex electric field in polluted insulators is proposed. The method is based on a quasi-static approximation which permits the decoupling of Maxwell's equations. The method is implemented numerically through the finite element technique by defining a complex functional View full abstract»

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  • Electrical reliability of dc-operated submarine telecommunications cables

    Publication Year: 1997 , Page(s): 1 - 9
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (868 KB)  

    The results of a research program carried out to quantify the reliability of joint moldings for dc operation in submarine telecommunications cables are reported. The region of the bulk insulation most at risk of electrical failure has been identified as the amalgamation zone of the molding, which is believed to be associated with additional electrical stress-enhancing defects present at the conductor-insulator interface. In addition to factory tests implemented to eliminate moldings with severely hazardous defects, a quality assurance sampling test procedure is proposed to optimize the manufacturing quality View full abstract»

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  • Dynamics of voltage polarity reversal as the controlling factor in space-charge induced breakdown of insulating polymers

    Publication Year: 1997 , Page(s): 44 - 51
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (712 KB)  

    Our investigation is focused on the understanding of high-field phenomena in polymers. In highly insulating materials such as polyethylene, space charge has a strong influence on both the short and long term breakdown strengths. The aim of this report is to demonstrate and discuss the importance of the dynamics of voltage polarity reversal at the injecting needle electrode on space charge induced breakdown. Evidence of space charge injection is provided by the observation of local breakdown generated by grounding of the sample after the polarization (so-called `grounding' tree). The effect which is polarity dependent, can be observed only when the sample is short-circuited immediately after charging. Field computation is performed versus injected charge and a critical charge density is derived in order to explain polymer breakdown upon grounding. The time dependence of the effect is explained by space charge relaxation. Polymer degradation under ac voltage is discussed on the basis of this interpretation View full abstract»

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  • Inference of Sampling on Weibull Parameter Estimation

    Publication Year: 1997 , Page(s): 146
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (100 KB)  

    First Page of the Article
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  • Kerr electro-optic field measurement and charge dynamics in transformer-oil/solid composite insulation systems

    Publication Year: 1997 , Page(s): 64 - 70
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (532 KB)  

    We measured the electric field in transformer oil/solid composite insulation system under dc voltage application using a Kerr electro-optic measurement system. When a pressboard was inserted at the center between two parallel-plane electrodes, the electric field at the mid-point between the pressboard and the cathode decreased with time. On the other hand, the electric field at the mid-point between the pressboard and the anode increased initially with time, reached a maximum value and then fell down. We measured also the electric field before and after polarity reversal of the dc voltage. The results revealed that the electric field after polarity reversal reached a magnitude 2.7× as much as the average dc applied field. We interpreted the above results on the time transition of the electric field in terms of a charge dynamic model, considering the difference in charge accumulation speed on the pressboard between positive and negative charges. This model was verified to be applicable to the time transition of the electric field in oil/solid composite system and BTA added oil/solid composite system as well View full abstract»

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  • Dynamic breakdown characteristics of liquid helium induced by a quench of superconducting wire and coil

    Publication Year: 1997 , Page(s): 120 - 126
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (800 KB)  

    For practical insulation design of superconducting power apparatus, it is necessary to take into account an inherent phenomenon known as quench, the transition from the superconducting to the normal state. We investigated quench-induced dynamic breakdown and prebreakdown characteristics of liquid helium (LHe). Experimental results revealed that the quench of the superconductor drastically reduced the breakdown voltage of LHe in the thermal bubble disturbance. Moreover, dynamic breakdown characteristics in a quasi-uniform field using a superconducting coil were investigated. The results revealed that the breakdown was induced in the quench-initiated region where the largest thermal energy was generated 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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