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Dielectrics and Electrical Insulation, IEEE Transactions on

Issue 3 • Date June 2003

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Displaying Results 1 - 19 of 19
  • Theoretical and experimental studies for spherical free-conducting particle behavior between nonparallel plane electrodes with AC voltages in air

    Publication Year: 2003 , Page(s): 404 - 417
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (941 KB) |  | HTML iconHTML  

    This paper deals with free-conducting particle motion and particle-triggered breakdown in AC electric fields between nonparallel plane electrodes in atmospheric air. Spherical particle motion was investigated theoretically and experimentally under AC voltages with various frequencies, considering the effect of the electrical gradient force and the dependence of the Coulomb force magnitude on the distance between a particle and an electrode. The result shows that when the Coulomb force acting on a bouncing particle changes its direction periodically under AC voltage whose frequency is around commercial power frequency, the electrical gradient force can become effective in initiating particle motion toward decreasing electrode gap regions, causing the particle to trigger breakdown. Moreover, it was found that the direction in which a particle advances horizontally is greatly influenced by microdischarge occurrence when the particle bounces very near to the grounded electrode under high-frequency AC voltage, and that when a particle bounces on an electrode, particle-triggered breakdown voltage is decreased by the effect of microdischarge. View full abstract»

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  • Electrical, microstructural, physical and chemical characterization of HV XLPE cable peelings for an electrical aging diagnostic data base

    Publication Year: 2003 , Page(s): 514 - 527
    Cited by:  Papers (27)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (986 KB) |  | HTML iconHTML  

    The aim of the European project "ARTEMIS" is to develop a diagnostic system for assessing aging in power cable insulation. Its first task was to make a thorough characterisation of the cable insulation before aging. This is intended to provide a background against which any changes introduced by thermo-electric aging can be identified. The aging markers derived from this initial characterisation will be considered both as diagnostic indicators in their own right, and also to develop an aging model for predictive purposes, if and when possible. This stage of the ARTEMIS programme is now complete and we will present an analysis of the results, and show how they may be correlated with the concepts proposed in aging theories. View full abstract»

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  • Experimental studies of free conducting wire particle behavior between nonparallel plane electrodes with AC voltages in air

    Publication Year: 2003 , Page(s): 418 - 424
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (553 KB) |  | HTML iconHTML  

    When a spherical conducting particle exists in an electrode system where electrical gradient force acts along the electrode surface, the particle tends to move towards the high field region. The possibility of appearance of this phenomenon is experimentally investigated with wire particles, which can easily produce the corona discharge on their ends resulting the action of a reactive force on the particle by a corona wind. The results show that a hovering particle travels deeper into the high electric field regions regardless of the corona discharge. Moreover, it is found that wire particle with corona discharge hovers near the negative electrode under DC voltage in atmospheric air due to different characteristics of corona discharge by the polarity. But under the AC voltage, the particle hovers near the bottom electrode only and invades in the high field region deeper than under the DC voltage. View full abstract»

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  • Surface characterization of new and aged semiconducting glazes

    Publication Year: 2003 , Page(s): 375 - 384
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (803 KB) |  | HTML iconHTML  

    A study is presented on changes in the structure and the chemical composition of antimony-doped semiconducting glazes before and after exposure to AC and DC electric fields in outdoor conditions and in the laboratory using the rotating-wheel-dip (RWD) test. Surface sensitive techniques such as scanning electron microscopy (SEM) in combination with energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS) and secondary ion-mass spectrometry (SIMS) were employed to characterize the materials. Aging in the form of crater building, surface cracking and pitting as well as formation of a tin oxide rich layer took place under both AC and DC exposure. However, the damage was much more severe under DC voltage. Similar aging changes could be obtained in the laboratory after only a few days of the RWD test. In the field, leakage currents were monitored for evaluating the electrical performance of the samples. On new samples, the currents varied only slightly depending on weather conditions. However, during rainfall periods the leakage currents on samples exposed to DC voltage for a longer period were significantly increased compared to the new state, while the currents on AC exposed samples remained unchanged. No flashovers occurred during the 4-month testing. Thermal runaway on samples exposed to DC voltage in the field caused the appearance of black spots in the glaze. Their origin and chemical composition are still under investigation. View full abstract»

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  • Toepler's spark law in a GIS with compressed SF6-N2 mixture

    Publication Year: 2003 , Page(s): 498 - 505
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (563 KB) |  | HTML iconHTML  

    This paper deals with the experimental measurements and analysis of the formative time lags to breakdown and an estimation of the Toepler's constant for gas gaps, under the application of 50 Hz AC voltage. The experiments were carried out in a 145 kV gas insulated system (GIS) bus duct with pure N2, pure SF6 and SF6-N2 mixture as insulating media. The formative time lags to breakdown in the gas gaps were measured using a fast response capacitive sensor. Toepler's spark law has been used to explain the breakdown phenomenon in the GIS and the values of Toepler's constant (kt), which gives an estimation of the formative time lags, were determined. Results show that the formative time lags vary inversely with gas pressure and the gas mixture concentrations for two gaps studied (0.46 mm and 0.61 mm). In the case of another gap (0.20 mm), the variation in the formative time lags with pressure as well as SE, concentration in the mixture has been found to be negligibly small between gas mixtures, although significant variation can be seen between pure SF6 and pure N2. Toepler's constant, kt, increases with gas pressure as well as SF6 concentration in the mixture for the gaps studied. Hence, kt is a function of the gas pressure and the concentrations of SF6 in the gas mixture for the above-mentioned gaps. View full abstract»

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  • Advanced PD inference in on-field measurements. II. Identification of defects in solid insulation systems

    Publication Year: 2003 , Page(s): 528 - 538
    Cited by:  Papers (52)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (782 KB) |  | HTML iconHTML  

    Results of investigations performed to evaluate the effectiveness of a new inference method for the diagnosis of solid insulation systems, based on partial discharge (PD) measurements, are reported in this paper. Signal separation, noise recognition, and PD source identification are the main features of the proposed inference method. Techniques for signal separation and automatic noise rejection are reported in the 1st part of this paper, while the problem of the identification of PD phenomena, occurring in defects of insulation systems, is approached in this 2nd part. The identification is based on fuzzy logic and enables the recognition of PD generated from different basic sources, such as internal, surface and corona discharges. It is shown that the different source typologies can be identified by means of fuzzy rules applied to a selection of parameters derived from PD-pulse phase and amplitude distribution analysis, once PD phenomena have been clustered in homogeneous class through a fuzzy algorithm based on PD-pulse shape. The proposed identification procedure is finally applied to rotating machines and cables, affected by insulation defects, showing promising on-field applications. View full abstract»

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  • Dynamic modeling of DC arc discharge on ice surfaces

    Publication Year: 2003 , Page(s): 463 - 474
    Cited by:  Papers (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (821 KB) |  | HTML iconHTML  

    A dynamic model for predicting DC arc behavior and critical flashover voltage of ice-covered insulating surfaces is presented. The model takes into consideration insulating geometry, pre-contamination level, and characteristics of ice layers. Assuming arc behavior as a time dependant impedance, it is possible to determine various arc characteristics such as time histories of leakage currents, potential gradient, channel radius, trajectory, propagation velocity and the energy injected into the zones free of ice (also called air gaps). The simulated results provided by the model are in agreement with those obtained experimentally using a simplified ice-covered cylinder as well as a short string of five IEEE standard porcelain suspension units covered with artificial ice. View full abstract»

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  • Motion behavior and deactivation method of free-conducting particle around spacer between diverging conducting plates under DC voltage in atmospheric air

    Publication Year: 2003 , Page(s): 444 - 457
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1071 KB) |  | HTML iconHTML  

    This paper deals with free conducting particle motion around different shaped spacers between diverging conducting plates under DC voltage in atmospheric air. Spherical particle motion was observed experimentally and the results were discussed on the basis of the electrostatic force acting on the particle with and without spacer. The results show that a particle around a spacer tends to move laterally towards or away from the spacer towards higher field regions, depending on the spacer configuration. It lifts at higher field positions and sometimes adheres to the spacer. The effects of spacer angle and spacer material (permittivity) on free conducting particle motion are also discussed. For comparing the results obtained with a sphere, a wire particle motion around different shaped spacers is also investigated. The obtained results suggest one of the methods to prevent/suppress the conducting particle from approaching or adhering to spacers, is to reduce the field strength in the vicinity of the triple junction of gas, solid dielectric and electrode in gas insulated system (GIS). View full abstract»

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  • Modelling of partial discharge development in electrical tree channels

    Publication Year: 2003 , Page(s): 425 - 434
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (656 KB) |  | HTML iconHTML  

    A model of partial discharge development in electrical tree structures is presented. The model considers channel conductivity, charge transport, and electric field redistribution during propagation of the discharge along the channels. It has been used for numerical investigation of temporal-spatial and electric characteristics of the partial discharges in capillaries and electrical trees exposed to AC voltage in a needle-plane geometry. The simulation results have been compared with experimental data given in the literature. View full abstract»

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  • The effect of humidity on the charge/phase-angle patterns of AC corona pulses in air

    Publication Year: 2003 , Page(s): 506 - 513
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (541 KB) |  | HTML iconHTML  

    AC corona pulses have been measured using a computer-based commercial partial discharge detector. The pulse height distribution was measured in air as a function of phase angle and pulse height for a range of voltages using a point/cup electrode system. An earlier paper discussed the effect of space charge on the onset voltages for both positive and negative half-cycles and on the patterns obtained. In the work reported in this paper, the humidity was varied, and large changes were found in the patterns observed in both half-cycles. At high humidities the negative half-cycle corona largely ceased but a second positive corona onset appeared in the second quarter of the cycle. An explanation for these phenomena is proposed in terms of the effect of the production of negatively charged water molecule clusters. Their production results in a lower effective ionization coefficient and thus higher critical field, and their lower mobility results in a more effective negative space charge. The former reduces the positive space charge in the positive half-cycle thus allowing avalanches and streamers to develop during the second quarter of the cycle. The latter results in a stronger negative space charge during the negative half-cycle which suppresses the corona during that half-cycle. View full abstract»

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  • Assessment of insulation condition of generator stator bars based on velocity of ultrasonic waves

    Publication Year: 2003 , Page(s): 539 - 547
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (621 KB) |  | HTML iconHTML  

    The velocity of ultrasonic waves, which were launched using the pulse-echo method and propagated in a stator insulation, was measured to assess the insulation condition of the stator bars. A statistical minimum velocity (Vmin) and a statistical average velocity (Vav) were computed for a new and three sets of stator bars which were in operation for 16, 18 and 23 years. After velocity measurements, several conventional electrical parameters such as dissipation factor, capacitance, and partial discharge were measured, and microscopic examinations of dissected insulation of tested bars were examined with a scanning electron microscope and an optical microscope. Experimental results showed that Vmin and Vav decreased and more microscopic defects were formed in the insulation with increasing operating time of the stator bar. For the three sets of aged stator bars, the insulation conditions based on Ymin and Vav were consistent with those assessed by measuring electrical diagnostic parameters. Therefore, Ymin and Vav were used to assess the insulation condition of large generators. The measurement of ultrasonic waves may offer a broad prospect for stator insulation diagnosis. View full abstract»

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  • Charge accumulation mechanism in oil/pressboard composite insulation system based on optical measurement of electric field

    Publication Year: 2003 , Page(s): 491 - 497
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (495 KB) |  | HTML iconHTML  

    It is important to investigate electrostatic charging phenomena in insulating oil pressboard (PB) composite system in electrical insulation design of oil-immersed power transformers. Our research aim was to clarify the charge accumulation mechanism at the oil/PB interface under static and flowing oil. In this paper, we directly measured the time variation of the electric field in the insulation system using a Kerr electro-optic technique. Results show the time decaying characteristics of an electric field in oil by charge accumulation. The results are influenced by oil flow conditions. Based on the measurement results, we propose a theoretical model for charge accumulation to clarify the process quantitatively. In the model we took the oil volume contributing to the charge accumulation into account, and analyzed the charge behavior. Finally, we clarified the charge accumulation mechanism at the oil/PB interface under oil flow conditions both with and without charging. View full abstract»

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  • About the significance of PD measurements in liquids

    Publication Year: 2003 , Page(s): 385 - 392
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (519 KB) |  | HTML iconHTML  

    This paper presents investigations concerning the variations and significance of PD measurements in mineral oil, when detectors with different frequency response are used. Typical durations of discharge phenomena in liquids are much longer than in other media, and the measurement technique must be adapted accordingly. However, depending on the application concerned, this is not always possible. In this study, experiments and calculations are carried out to determine typical errors produced when classical RLC measurement impedances with various frequency responses are used to measure PD's in liquids. Experiments are done with corona and creeping discharges in mineral oil, and compared with corona and spark discharges in air. These examples allow us to conclude that when a calibrated high frequency PD measurement system is used, the ratio of measured to actual charge is much lower for discharges in liquids than in gases. If measurements are carried out on a practical device that may include various types of PD sources, the high frequency measurement system will strongly underestimate discharges in liquids compared to other discharge types. This discrepancy versus discharge type increases when the frequency response of the measurement system is increased. View full abstract»

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  • More accurate breakdown voltage estimation for the new step-up test method

    Publication Year: 2003 , Page(s): 475 - 482
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (480 KB) |  | HTML iconHTML  

    The step-up method is used to estimate the impulse breakdown voltages when the electrical insulation is not usable after it is broken. This paper analyses the reliability of the estimates of the underlying breakdown probability distribution in the step-up method, when (1) the observed breakdown voltage itself is available and (2) it is not available. The former case has many advantages compared to the latter case such that (i) the confidence intervals of the estimates become smaller and (ii) the estimates can be obtained with higher probability. Consequently, this paper recommends using the estimates of the underlying distribution for the breakdown voltages instead of the nominal breakdown voltages. Some illustrative examples are given. View full abstract»

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  • Three-dimensional space charge observation of ion migration in a metal-base printed circuit board

    Publication Year: 2003 , Page(s): 458 - 462
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (487 KB) |  | HTML iconHTML  

    Internal space charge measurement has been mainly applied to investigate insulating materials used in RV apparatus, such as HVDC cables. We have observed the space charge profiles to monitor copper ion migration occurring in an insulation layer of a metal-base printed circuit board and found that the space charge distribution along the thickness direction corresponds to the progress of ion migration in insulation. The migration, however, can proceed in any direction in the specimen simultaneously; therefore, it should be measured in three dimensions. We measured metal-base epoxy resin insulated printed circuit boards by a newly developed three-dimensional pulsed electroacoustic method. The results show that the space charge density varies in the lateral direction when ion migration occurs in the specimen. View full abstract»

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  • Determination of the step response function of a dielectric in the presence of noise

    Publication Year: 2003 , Page(s): 369 - 374
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (380 KB) |  | HTML iconHTML  

    In the time domain characterization of dielectrics a fundamental measure is the dielectric response function Φ(t). This function permits the relaxation time and the complex permittivity of the dielectric under test to be determined, allowing the complete characterization of the dielectric properties. To calculate the Φ(t) function a time domain deconvolution algorithm (TDD), developed in a previous work, is employed. In this paper a new technique to enhance the calculation of the Φ(t) function in the time domain, is presented, avoiding the instability problems inherent to the TDD algorithm. The method consists in the use of appropriate digital lowpass filter in several stages of the time domain deconvolution algorithm to calculate the Φ(t) function. This procedure provides an enhanced precision for Φ(t) even for very short times (≈ 10 ps for the time domain reflectometry system used). View full abstract»

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  • Effects of manufacturing technology on electrical breakdown and morphology of thin films of low density polyethylene blended with polypropylene copolymer

    Publication Year: 2003 , Page(s): 435 - 443
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (648 KB) |  | HTML iconHTML  

    Extruded films prepared from blends of low-density polyethylene (LDPE) and random copolymer of ethylene and propylene (EP) with the T-die method were studied with respect to electrical properties and morphology. Comparisons with data on blown films are made. These blends are of interest as improved LDPE for making XLPE for insulated power cable. In the high temperature region (90°C), a specimen with a slightly higher EP content had higher impulse breakdown strength than that with a lower EP content, but no improvement of DC breakdown strength by blending could be found. The improvement of impulse breakdown strength (90°C) is explained in terms of morphological changes by blending such as the orientation of chains in a film and the size of spherulites on the assumption of the thermal breakdown. In comparison, a T-die film had higher impulse breakdown strength than that of a blown film for the same composition. The impulse breakdown strength also increased with the use of the higher density LDPE. In the current versus electric field characteristics at 30°C, the blend polymer with EP content of 5-10% showed a transition from LDPE behavior at low field region to EP behavior at high field region. However, no appreciable difference in current behavior among the specimens was observed at 90°C, which suggests an incompatibility between the two materials that exists at 30°C but not at 90°C. View full abstract»

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  • Effect of semiconducting screen on the space charge dynamic in XLPE and polyolefin insulation under DC and 50 Hz AC electric stresses conditions

    Publication Year: 2003 , Page(s): 393 - 403
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (681 KB) |  | HTML iconHTML  

    In the past two decades, significant advances in space charge measurements in polymers have resulted in a better understanding of charge dynamics and their effect on material selection and processing. However, little attention has been given to the effect of semiconducting screens on space charge formation in the bulk insulation. This paper reports on space charge measurements on ∼ 1.5 mm thick XLPE and polyolefinic plaques with different treatments and semicon electrodes, using the modified laser induced pressure propagation (LIPP) system. Samples were subjected to DC or 50 Hz AC electric stresses in the region of 25 kV/mm at ambient temperature. Emphasis has been placed on comparing the space charge characteristics of the two insulation systems with different semicon electrodes using an established method termed "X-plots" for analyzing data. The effects of sample treatment (i.e. degassing) on the space charge dynamics are also presented. View full abstract»

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  • The influence of the dielectric strength of the N2/SF6-insulation by conducting particle on the spacer surface

    Publication Year: 2003 , Page(s): 483 - 490
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (592 KB) |  | HTML iconHTML  

    This paper investigates the dielectric properties of various N2/SF6 gas mixtures based upon a cylindrical spacer model with adhering particle on the surface tinder homogeneous field conditions. The investigation involves a comparison with pure SF6. The flashover field strength for clean and particle contaminated spacer surface under AC and LI stress is determined. The results of the investigations show the sensitivity of N2/SF6 gas mixtures to conducting particles on spacer surfaces for gas pressures up to 800 kPa. Moreover, the correspondence between pure SF6 at pressure range from 100 to 400 kPa and N2/SF6 gas mixtures for AC and lightning impulse (LI) flashover field strength range from 50 to 178 kV/cm is determined. Conclusions are drawn about the ability of SF6 gas mixtures to serve as technically efficient media for GIS/GITL. The results shed light on the issue of the SF6 reduction and particle detectability in GIS/GITL. 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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