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Electrical Insulation and Dielectric Phenomena, 2009. CEIDP '09. IEEE Conference on

Date 18-21 Oct. 2009

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Displaying Results 1 - 25 of 184
  • Development of highly thermoconductive epoxy composites

    Publication Year: 2009 , Page(s): 638 - 641
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (443 KB) |  | HTML iconHTML  

    Epoxy resins with controlled high-order structures show higher thermal conductivity than conventional ones, because the ordered-structure domains consisting of self-arranged `mesogen' groups of epoxy monomers promote smooth phonon transportation. In this report, we investigated composites consisting of these resins and ceramic fillers to obtain epoxy resin composites having both high isotropic thermal conductivities and electrical insulation. Though these epoxy monomers are difficult to handle because of their crystallinity and poor solubility in solvents, we confirmed that the conventional processes for thermosetting resin forming, such as "varnish coating" and "transfer molding", are applicable to these composites by optimizing the molecular architectures of hardeners, the composition of solvents, etc. As a result, excellent thermal conductivity (i.e., higher than 10 W/mK) was attained for the composites using the developed mesogen type epoxy monomers. View full abstract»

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  • Calculation of partial discharge inception voltages in ultradilute SF6 + N2 gas mixtures

    Publication Year: 2009 , Page(s): 531 - 534
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (439 KB) |  | HTML iconHTML  

    This study proposes a method of calculation to estimate partial discharge inception voltages in ultradilute SF6 + N2 gas mixtures. The method is based on the condition necessary for the initial streamer to propagate in a gap where the electric field distribution is highly non-uniform. The proposed method utilizes the finite element method (FEM) in determining the electric fields in ultradilute SF6 + N2 gas mixtures. The analysis is applied for rod-plane gaps. Since the average errors are less than 5%, it is recommended to use the proposed simulation model to predict partial discharge inception voltages in ultradilute SF6 + N2 gas mixtures. View full abstract»

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  • Technical advancements in the integration of online partial discharge monitoring in distribution cable networks

    Publication Year: 2009 , Page(s): 323 - 326
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (218 KB) |  | HTML iconHTML  

    Online partial discharge (PD) detection and location systems for medium-voltage (MV) cables have been developed over the past years and are currently introduced by utilities on an increasingly large scale. This paper addresses a few of the new challenges related to the integration of these systems in various cable networks. The effect of ring-main-units (RMUs) and substations on the propagation of PD signals is studied to determine feasible options for PD monitoring on two consecutive cables connected through an RMU or a substation. Different algorithms for PD pulse arrival time estimation are analyzed for robustness and PD origin location accuracy. An algorithm based on the signal energy proved to be most suitable for complex circuits where the PD shape is not only distorted by the propagation through the cable, but also by complex impedances in the RMUs along the cable under test and each cable end. Matched filters for PD detection can be improved using measured PD signals. This results in improved detection sensitivity and location accuracy. View full abstract»

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  • Reducing air clearance requirements for voltage uprating of overhead line by use of line surge arresters

    Publication Year: 2009 , Page(s): 224 - 229
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (294 KB) |  | HTML iconHTML  

    While uprating an overhead line to a higher voltage level, it is often difficult to achieve the required clearance level for the uprated structure. Use of Transmission Line Arresters (TLAs) is an effective technique in controlling overvoltages and thereby, achieving the required clearance margin. In this paper, suitability of this technique in reducing the clearance margin is discussed. A case study on uprating an existing 275 kV overhead line to 400 kV is investigated here. View full abstract»

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  • On the conductivity of pure epoxy in time and frequency domain

    Publication Year: 2009 , Page(s): 108 - 111
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (219 KB) |  | HTML iconHTML  

    This paper contains examinations concerning the conducting behavior of pure epoxy resin in time and frequency domain First, time resolved current measurements are presented to analyze the behavior in time domain experimentally. The conducting behavior is recorded in dependence of temperature and applied DC-voltage. Based on the experimental examinations an equivalent circuit diagram is developed which offers the possibility to simulate the measured charging and discharging currents and to perform frequency depending examinations in the range significantly lower 1 Hz. View full abstract»

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  • ICAAS — Integrated system for lasting accelerated aging of MV cables, data monitoring and acquisition

    Publication Year: 2009 , Page(s): 35 - 38
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (343 KB) |  | HTML iconHTML  

    A reliable knowledge of the network components condition is of primary importance for creating an optimal investment and maintenance plan for electrical distribution networks. A commonly used tool for this purpose is a partial discharge measurement and analysis. It enables a good overview over the electrical equipment condition and in this way also a prediction of possible service failures. In the case of paper insulated lead cover (PILC) cables, there are still no established criteria for assuming the time to the next failure. Therefore, an accelerated aging system assigned to this cable type was developed, built up and tested. It facilitates a highly sensitive and selective PD-detection and accurate tan(o¿)-measurements. Furthermore, by the constant monitoring of the entire aging process, a knowledge data-base is formed up, and the later development of sophisticated diagnostic criteria based on the physical aging process is made possible. In this paper the basic principles and the functionality of a novel system for the accelerated ageing of MV cables called ICAAS (Integrated Cable Accelerated Ageing System) are presented. View full abstract»

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  • Preliminary study on detection of PD under oscillatory impulse voltage

    Publication Year: 2009 , Page(s): 348 - 351
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (283 KB) |  | HTML iconHTML  

    In order to study the partial discharge (PD) pulses under oscillatory impulse voltage (OIV), an oscillation waveform generator is designed and the waveform parameters expressions are presented based on the equivalent circuit model; A high-frequency current transducer is developed for measurement of PD. Then the effects of coil turns and integral resistance on frequency properties are studied. Moreover, calibration and analysis of the actual dynamic response are performed by adopting function generator and square-wave source; The PD measurement system to detect the PD signals of needle-plate model under OIV is provided finally. Experiment shows that by adopting this PD measurement system, the source interferences are restrained and PD signals are effectively extracted, therefore it could be a worthy approach not only for further study on PD character under OIV, but also to explore the mechanism behind it. View full abstract»

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  • Tracking behaviour in the presence of conductive interfacial defects

    Publication Year: 2009 , Page(s): 230 - 233
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (399 KB) |  | HTML iconHTML  

    The study presented in this paper aim at extending the knowledge on how interfacial defects in composite insulation systems may affect surface tracking under contaminated conditions. Model samples mimicking an inter-facial conducting defect were made of high temperature vulcanised silicone rubber moulded on epoxy substrate with a circular metallic foil inserted at the interface. They were tested for the tracking resistance by means of the inclined plane test procedure. The samples with defects exhibited shorter time to track compared to reference samples without defects. In addition the tracking was more severe on the defected samples. Electric field simulation performed in parallel revealed that presence of surface contamination increases the distortion of electric field around the defect and thus explain both the effects of more severe damage of material surface and lower time to tracking experienced in this study. View full abstract»

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  • Evaluation of dielectric properties in polypropylene/clay nanocomposites

    Publication Year: 2009 , Page(s): 507 - 510
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (313 KB) |  | HTML iconHTML  

    Effects of nanoflller addition on four typical dielectric properties, namely permittivity ¿¿', dielectric loss factor ¿r¿, space charge accumulation, and partial discharge (PD) resistance were evaluated for polypropylene (PP) and its nanocomposites (NCs) with nanoclay. While ¿r' and ¿¿" are almost independent of temperature and frequency in the base unfilled PP, they are highly dependent on the two parameters in the two NCs. Namely, ¿r' increases significantly at temperatures above 20°C and the frequency spectrum of ¿¿" shows at least one temperature-dependent peak. Furthermore, space charge appears abundantly in the two NCs compared to the base PP. These results indicate that plenty of mobile carriers and/or dipoles, probably resulted from the manufacturing process, remain in the two NCs. Notwithstanding the above-mentioned 'inferior' insulating properties, the two NCs have an improved PD resistance compared with the base PP. Namely, the erosion depth on the surface induced by PDs is the smallest in the NC with the largest filler content, while it is the largest in the base PP. Such differences in the effects of nanofillers on different insulating properties are attributable to the fact that nanofillers can improve the PD resistance simply by their presence, while the chemicals needed for uniform dispersion of nanofillers may sometimes increase the permittivity and abundance of charge carriers. View full abstract»

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  • Role of the interface on charge build-up in a low-density polyethylene: Surface roughness and nature of the electrode

    Publication Year: 2009 , Page(s): 112 - 115
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (177 KB) |  | HTML iconHTML  

    The aim of this work is to better understand the impact of the nature of the metal and of the surface topology on the charge generation at a metal / dielectric interface. Conduction current and space charge measurements using the pulsed electro-acoustic method (PEA) have been carried out on low density polyethylene (LDPE-A) films with different metal electrodes (Au, Al, Ag, In) in order to evaluate the role of the carriers (hole, electron) injection barrier height on the charge build-up. The impact of the roughness of the interface has also been theoretically investigated. Experimental surface profiles have been introduced in a model able to simulate the surface roughness in two dimensions, and to calculate the electric field and the injection current. View full abstract»

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  • Partial discharge diagnosis for transformer — One step toward strong smart grid in China

    Publication Year: 2009 , Page(s): 352 - 355
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (577 KB)  

    This paper presented four cases of online/offline partial discharge (PD) diagnosis in various scenarios. Some case gave strong evidence of PD occurrence but no discharge signal was detected. Some case gave obvious PD signal pattern, which was identified as noise. In the last case, a small PD phenomenon was identified and located by a combination of several diagnostic methods, including dissolved gas analysis, leakage current analysis, and PD detection through pulse current signal and ultra sonic signal. The results show that online PD detection was useful but complicate. The information can be conflicting and misleading. A comprehensive understanding of test condition and an in-deep study of the measurement results is essential in such diagnosis. View full abstract»

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  • Partial discharges of thermally and electrically aged insulation

    Publication Year: 2009 , Page(s): 39 - 42
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (229 KB) |  | HTML iconHTML  

    The working life of electrical machines is primary affected by the insulation system quality. Diagnostics methods help to understand the momentary state of insulation and to avoid the possible damage or electrical breakdown of machines through the repair or insulation rewinding. Partial discharges testing belongs to one of the high applicable test method of insulating materials within electrical machines. The described experiment consists of laboratory thermal and electrical aging of main wall insulation and consequently testing of partial discharges. The test material consists of resin rich mica composites based on glass fabric and epoxy resin. The flat specimens of insulation were cured and thermally and electrically aged and the partial discharges were measured accordingly. The thermal aging was performed at four different temperatures (170, 175, 180, 186°C) at different times. The electrical aging was completed at two different voltage levels (10, 12 kV) at different times. The flat specimens were tested at special electrode setup. The conductive rubber electrodes were used to avoid the gliding discharges on the surface of specimen. The trends of partial discharge main parameters (ignition voltage, extinguish voltage, pulse count, average discharge current, peak charge level) are studied and described in dependence on exposure time, temperature and applied voltage. View full abstract»

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  • Dielectric integrity of silica-PAI nanocomposites at elevated temperature

    Publication Year: 2009 , Page(s): 535 - 538
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (514 KB) |  | HTML iconHTML  

    It has been shown that in many cases, the addition of nanoscale metal oxide fillers to polymers leads to an improvement in dielectric breakdown strength at room temperature. However, in some cases electrical insulation is exposed to elevated temperatures. A thermally stable polymer material, such as polyamideimide (PAI), is desired for these applications. For this reason, breakdown strength measured at elevated temperatures is required, since this property is expected to degrade with an increase in temperature. The addition of nanoparticles has been shown to increase PAI decomposition temperature and is also expected to mitigate the effect of increased temperature on dielectric properties. In this paper, AC and DC breakdown strength of PAI and nanosilica filled PAI are reported at room temperature and elevated temperatures. (200-340°C) Test temperatures were well below the decomposition range of polyamideimide as measured by thermogravimetric analysis (TGA). Silica composites at all loadings (whether treated or untreated) were shown to have a higher AC and DC breakdown strength at elevated temperatures than unfilled material. Dielectric spectroscopy results are also presented. View full abstract»

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  • High thermal conductive laminates for large current

    Publication Year: 2009 , Page(s): 642 - 645
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1170 KB) |  | HTML iconHTML  

    In order that resins such as laminates may be made resistant to heat arising from the higher voltage or larger current of power device, it is necessary to make them highly thermally conductive. To make resins highly thermally conductive, it is usual to use a compound with inorganic filler. However, the thermal conductivity of matrix resins is low compared to that of ceramics. To achieve high thermal conductivity, it is necessary to use a large number of fillers. On the other hand, if the resin itself, which is a matrix, is highly thermally conductive, the thermal conductivity of compound resin can be efficiently improved. We have found that the thermal conductivity of the resin itself can be improved with the ordered structure of liquid crystal epoxy resin, which contains a mesogen group in the main chain. In this report, attention was paid to the resin that showed a smectic liquid crystal phase with higher regularity in order to improve molecular regularity in this ordered structure. In result, the thermal conductivity of this resin was 2.3 times that of usual epoxy resin and 1.4 times that of liquid crystal epoxy resin that shows a nematic phase. With laminates using this smectic-phase resin, a thermal conductivity of 11.4 W/m-K maximum was achieved. View full abstract»

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  • Effect of crystallinity on the partial discharge resistance of poly-L-lactide

    Publication Year: 2009 , Page(s): 539 - 542
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (425 KB) |  | HTML iconHTML  

    We have changed the crystallinity of biodegradable poly-L-lactide (PLLA) by drawing or by annealing thermally, and have examined its effect on the partial discharge (PD) resistance. Although the depth eroded by a fixed period of PD degradation becomes shallower when the sample was crystallized by the drawing or by the heat treatment, its reduction ratio is almost equal to the reduction ratio of PD activities due to the decrease in permittivity. Therefore, it is hard to assume that crystallization of PLLA improves its PD resistance to a unit amount of charge. View full abstract»

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  • Complex permittivity spectra of several insulating polymers at electrical and THz frequencies

    Publication Year: 2009 , Page(s): 7 - 10
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (293 KB) |  | HTML iconHTML  

    Frequency and temperature dependencies of the real part (¿r') and imaginary part (¿r ") of relative complex permittivity were measured at electrical frequencies from 10-2 to 105 Hz at temperatures from -80 to 200°C for various kinds of organic insulating polymer films. Furthermore, frequency spectra were obtained at 30°C in a frequency range from 0.4 to 4.0 THz for both parts. As a result, it was found that there are significant differences in both the temperature and frequency dependencies of ¿r' and ¿¿", depending mainly on the polymer being polar or nonpolar. By comparing terahertz (THz) time-domain spectra obtained for various polymeric insulating films such as polyamide and poly(L-lactide), it was found that the polar polymers have one or two distinct dielectric loss peaks around 2.0 and 3.0 THz. More specifically, among the polymers examined, only polyamide has both two peaks, while poly(L-lactide) and polyethylene terephthalate have only one peak. Nonpolar polymers show no peaks. Furthermore, it has become clear that ¿r' approaches almost the same value of 2.3 at 3.8 THz in most polymers including polar ones. This agrees with the fact that only electronic polarization and atomic polarization associated with very light atoms such as hydrogen can participate in polarization at such high frequencies. View full abstract»

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  • Tree initiation and growth in LDPE/MgO nanocomposites and roles of nano fillers

    Publication Year: 2009 , Page(s): 646 - 649
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (228 KB) |  | HTML iconHTML  

    Processes of tree initiation and growth in LDPE/MgO nanocomposites were investigated by using optical and partial discharge (PD) detection methods. They can be divided into three stages depending on tree length. The first stage corresponds to the initial growth of about 10 ¿m and might be subtly affected by the filler content up to 1 phr. This might be influenced by Coulombic field formed around nano fillers. The second stage is interpreted as tree growth around 100 ¿m, and is suppressed by nano fillers up to 2 phr, where trees grow by colliding with nano fillers. The third stage leads to final breakdown at which tree lengths are of 1 mm order, and are retarded by nano fillers up to 10 phr, where PD erosion processes are involved. View full abstract»

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  • Ester fluids as alternative for mineral oil: The difference in streamer velocity and LI breakdown voltage

    Publication Year: 2009 , Page(s): 543 - 548
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (435 KB) |  | HTML iconHTML  

    Mineral oil has predominantly been used as the insulation and cooling liquid in transformer industry for more than 100 years. However, with the concern of fire safety and environmental impact alternative liquids such as ester fluids are of interest. In fact, these liquids are biodegradable, less flammable and have been used in thousands of distribution transformers world-wide. A trend has been seen in recent years that these fluids have been introduced in power transformers. With the aim at qualifying the dielectric performance of ester fluids for use in medium and large power transformers, the authors' group has carried out research work during the last 5 years. Part of results is reported in this paper. In the investigation, needle/plane geometry was used. A streamer was generated at the needle tip and propagated across the oil gap or along an oil/pressboard interface. Breakdown voltage, polarity effect, streamer velocity and acceleration voltages for transition to fast event were studied. Findings show that the streamer fast event feature in ester fluids was quite different from that in mineral oil especially at positive polarity, where significantly lower breakdown voltage values were observed in ester fluids than in mineral oil over long electrode gap distances, and that the transition voltages to fast event in ester fluids were much lower than those in mineral oil and that fast event streamer velocity in ester fluids increased much more steeply at over-voltages than in mineral oil. Electrode gap distances of 25 mm, 100 mm and 200 mm were tested at LI (lightning impulse) voltages of 1.2/50 ¿s. Streamer velocity up to 120 km/s was recorded. Results are summarized and analyzed. The work contributes to the understanding of the dielectric properties of ester fluids and mineral oil for the insulation system design of medium and large power transformers. View full abstract»

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  • Withstand voltage testing in combination with PD measurements of XLPE cables under damped alternating voltage on-site

    Publication Year: 2009 , Page(s): 43 - 46
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (308 KB) |  | HTML iconHTML  

    As an after-laying test, withstand voltages and PD measurements of XLPE cables on-site have been finished respectively for many years. Standard test procedures using continuous AC voltages are very cost intensive due to the high capacitive power demand of the cables and the resulting large sizes of the test sets. The contribution paper presents that withstand voltage testing in combination with PD measurements of XLPE cables will be done at the same time under damped alternating voltage on-site. Based on the field experiences including withstand voltage testing and PD detections, a damped alternating current (DAC)voltage generator and a transducer of PD pulse measurement were developed in the laboratory. We established a typical defects model of 10 kV XLPE power cables. For these samples, the applied voltage peak value is from 14-34 kV, simultaneously the PD is measured. The insulation conditions of the samples can be evaluated according to the records of withstand voltage tests and non-destructive dielectric tests. Based on these test models, this paper deems that the damped alternating voltage is an effective test method showing a very high sensitivity of PD detection and recognition of electrical treeing for XLPE cables on-site. using the damped alternating voltage, Both voltage withstand testing and partial discharge testing are made at the same time, we can confirm roundly and accurately the situation of XLPE cables. The future work is that a large of field data based on real XLPE cables needs to accumulate for a long time. In particular, the database of PDs need to set up. View full abstract»

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  • Capacitance behavior of electric double layer capacitor using nanocomposite electrode

    Publication Year: 2009 , Page(s): 116 - 119
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1380 KB) |  | HTML iconHTML  

    In this study, capacitance behavior of electric double layer capacitor (EDLC) with nanocomposite electrode for energy storage has been examined by charge-discharge characteristics. Also, internal resistance of EDLC was evaluated using two kinds of conducting filler. The one is acetylene black (AB) and the other is Ketjenblack (KB). KB was used for polarized electrodes instead of conventionally used AB in order to improve the capacitance and to decrease the internal resistance of EDLC. Usually, KB exhibits higher electronic conductivity compared to AB, and KB could be considered as conducting filler. The temperature dependence of capacitance and internal resistance of prepared EDLC using aqueous electrolyte, organic electrolyte and 2 kinds of ionic liquid was evaluated. Also, adsorbed ion numbers on the surface of KB and pore utilization of KB on each electrolyte was evaluated. As the results, it was found that the KB containing EDLC showed fairly high capacitance compared to AB containing one on all electrolyte. In addition, temperature dependence of EDLC containing KB and AB were measured on temperature from 0°C to 50°C. It was understood that KB was superior to AB in all temperature and all electrolyte on capacitance and internal resistance. Moreover, adsorbed ion numbers on the surface of KB and pore utilization of KB was high using aqueous electrolyte. View full abstract»

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  • Investigation on transformer oil impedance during breakdown under AC voltage

    Publication Year: 2009 , Page(s): 549 - 552
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (175 KB) |  | HTML iconHTML  

    In this paper, we present an experimental study on the properties of mineral oils under AC breakdown conditions. Breakdown tests were carried out on mineral oil samples using a sphere-sphere electrode test cell for various gap lengths 1 mm, 2.5 mm and 5 mm and at different voltage speed ramps: 0.5 kV/s, 2 kV/s and 3.5 kV/s. The dynamic impedance of the mineral oil samples was determined from the instantaneous ratio of voltage and current. Such dynamic impedance can be used to explore the properties of the arc and its development within the oil. The results of this investigation show that the gap length and the voltage speed ramp have a significant influence on both the impedance magnitude and the decay time taken to reach the minimum impedance. View full abstract»

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  • Evaluation of influence of mineral oil immersion on dielectrical properties of silicone polymers by Thermal Analysis

    Publication Year: 2009 , Page(s): 327 - 330
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (117 KB) |  | HTML iconHTML  

    In this paper ageing phenomena of polymer insulating materials due to exposure to mineral oil is investigated with focus on dielectrical properties of cable insulations. Silicone specimens were immersed into mineral oils such as gasoline, diesel fuel or motor oil. The dielectric parameters show a significant increase both in permittivity and loss factor. A Simultaneous Thermal Analysis has been performed in order to indicate changes in specimen polymer structure. It could be shown that the specimens with decreased electrical performance suffered from permanent chemical degradation. View full abstract»

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  • Some peculiarities of breakdown voltage computation in non-uniform electric field by impulse impact

    Publication Year: 2009 , Page(s): 553 - 556
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (204 KB) |  | HTML iconHTML  

    A numerical model of positive streamer is developed. One-dimensional approximation is used to describe the streamer channel whereas processes near the streamer head are considered as an axisymmetric two-dimensional problem. Results of the computation are compared with commonly known data about a streamer. View full abstract»

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  • Some unexplained disturbing phenomena in the electrical properties of dielectric polymers

    Publication Year: 2009 , Page(s): 723 - 726
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (159 KB) |  | HTML iconHTML  

    In this paper, we address some poorly explained problems associated with electrical properties of dielectric polymers. Charge injection is often unclear due to metal-polymer interfaces phenomena including poor contacts, asperities and electrochemical reactions. We also review some difficulties involving the sample bulk, the most important being the influence of the sample size on aging and breakdown. We show many results obtained with a wide variety of (reasonably pure and defect-free) polymers suggesting that in addition to thickness, the electrodes area is also a parameter. The negative resistance often observed in conductivity measurements is also discussed. The fact that C-C bonds are more easily broken than expected implies that this phenomenon must be looked at more carefully. The role of the free radicals thus created requires more attention. It is suggested that the interpretation of several measurements, mobility for example, might require some revision. Among other things, interpreting results using only an activation energy is not likely to give a correct description of the measured phenomenon since entropie effects are quite significant with most polymers. Finally, one may wonder if the usual explanation for some trapped sites in the so-called forbidden band of polyethylene still makes sense considering the fact that charge transport is mainly affected by the bonds broken by the applied stress. View full abstract»

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  • High field effects on the electrical aging of polyethylene and of polypropylene

    Publication Year: 2009 , Page(s): 47 - 50
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB) |  | HTML iconHTML  

    In this paper, we show that the electrical aging equation for polyethylene and polypropylene under high fields (above 100 kV/mm) require and additional term, which is the strain energy (sometimes called the electromechanical energy). This term becomes significant at high fields when the electromechanical stress thus generated compress the tested sample. From a practical point of view, this means that life could be a bit longer than expected at very high fields. Examples with the two above polymers are shown along with the corresponding calculated activation volume and the strained activation volume. The stress at which the strain energy becomes significant can also be calculated from the mechanical properties of the polymer. This makes the aging equation a little bit more complicated than we expected but it is still possible to relate the fast breakdown measurements with long lasting endurance tests. View full abstract»

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