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Electrical Insulation, 2000. Conference Record of the 2000 IEEE International Symposium on

Date 2000

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Displaying Results 1 - 25 of 124
  • Investigation of the relative impulse strength of magnet wires

    Page(s): 239 - 242
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB)  

    This investigation was conducted to determine if shielded magnet wire was really superior to heavy and quad build wire for use in large (up to 900 hp), random wound AC motors. Since all motors start cold (at least once), we determined that testing at room temperature was not unreasonable and that further testing at elevated temperatures could be done, if needed. We also tried to establish a relationship between the AC and impulse breakdowns. To this end, we manufactured 150 medium sized three turn coils with two 15 AWG wires in parallel. We used five types of magnet wire (heavy build from two manufacturers, shielded wire from the same two manufacturers and quad build from one of these manufacturers). We applied voltage between the parallel wires at an increasing rate (of 1000 volts per second) till breakdown to ten coils of each type. We used AC voltage and 0.1 microsecond wavefront pulses using a commercial surge test set (60 impulses per second). Two voltages were used for each test sequence, so that rudimentary voltage endurance curves could be developed. The results are shown for each of the five types of wire View full abstract»

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  • The breakdown behavior of impulse stressed polyethylene in dependence on the parameters characterizing lightning impulses

    Page(s): 119 - 122
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    Investigations on the influence of various lightning impulse stresses, with and without superimposed oscillating voltages of various frequencies and amplitudes, on the impulse voltage strength of polyethylene, are presented. The experimental investigations result in conclusions about the breakdown behavior of impulse stressed polyethylene, thus leading to a discussion about the necessity for modifications of the actual standards in which lightning impulse tests are defined, in order to make them more convenient for the future View full abstract»

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  • A study about the influence of the rise-time of quasi-square voltages on the aging by partial discharges of a polymeric film

    Page(s): 21 - 23
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    An experimental study about the influence of the factor dv/dt, which characterizes inverter supply quasi-square voltages, on the behaviour of a polymer film (PET) subjected to aging by partial discharges (PDs) has been performed. The outcome of special laboratory aging tests confirmed that the dv/dt plays a role in the aging process. The analysis of the times-to-failure data evidenced that a minimum time is found when increasing the dv/dt value. Also, the analysis of the acquired PD signals relevant to the partial discharges shows that the dv/dt values do not strongly affect the PD activity View full abstract»

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  • Space charge development and breakdown in cross-linked polyethylene under DC fields

    Page(s): 489 - 492
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    Space charge development in cross-linked polyethylene (XLPE) was investigated using the Thermal Step Method (TSM). The samples were subjected to DC fields of ~25, 50 and 70 kV/mm and, several times during aging, the TSM, which is a nondestructive technique, was used to measure insulation response current. The distribution of the corresponding space charge was computed using the newly developed inverse matrix technique. The insulation response current increased systematically with the time of voltage application. Under similar aging conditions some specimens were found to develop space charge faster than others. These specimens have consistently failed sooner than those with slower rate of space charge buildup. It is proposed that the initial rate of space charge development in polymeric insulation could provide an indication of its performance under DC field View full abstract»

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  • PD patterns and current shapes of artificially-simulated tree channel

    Page(s): 328 - 331
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    In order to clarify PD mechanism and degradation of electrical tree in solid polymer insulator, PD patterns, pulse sequences and current shapes in an artificially simulated tree channel were investigated. A few hours after voltage application, new tree channels started to propagate. When they were propagating, the voltage increment between two consecutive PD pulses was constant in positive polarity in spite of PD magnitude changing. Furthermore, there were at least two types of PD current shapes in the same positive half cycle. This result suggests that there are different mechanisms of PD's in the same half cycle View full abstract»

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  • Investigations on cavities inside liquid-immersed paper and pressboard insulation materials and their influence on the electrical behavior

    Page(s): 422 - 425
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    Although the process of impregnating cellulosic materials with liquid insulants is well known and has been in use for many decades sometimes problems with gas-filled cavities inside the impregnated material still arise. Therefore extensive experimental investigations on the effects of gas-filled cavities inside an impregnated pressboard, like they appear after an imperfect impregnation, have been performed. The filling of hidden voids with surrounding insulation liquid during and after impregnation process was examined and the results are presented in this contribution. Using defined failures inside a transformerboard also the influence of these defects on the electrical behavior of the insulation in a semi-uniform field was simulated View full abstract»

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  • Changing insulation systems-benefits and problems

    Page(s): 148 - 156
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    In the last decade there have been numerous advances made in insulating tapes, resins, test methods and instrumentation. The impact of the application of the newer tapes and resins has produced step surges in insulation technology. The primary emphasis has been on the reduction of the total insulation in the machines to achieve higher output density, improved heat transfer, improved efficiency and performance. The enhancements in test methods and equipment have served to increase the predictive accuracy of pending failures and to improve the integrity of the insulation system. Methods designed to find failures are now used to predict weakness and improve the insulation processes. As the demands on insulation systems are increased, failure mechanisms that were infrequent are starting to become more common. This paper will look at one manufacturer's vision of the future of insulation technology as it applies to the design of rotating equipment. It will also discuss the use of insulation evaluation techniques in insulation design, and will review insulation failure mechanisms and problems View full abstract»

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  • Development of a submerged winding induction generator for cryogenic applications

    Page(s): 243 - 246
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    This paper discusses the development of a series of one-megawatt, 3.3 kV variable speed input, constant frequency output induction generators to be used while totally submerged in liquid methane at -161°C. The specific purpose and application of these induction generators was to increase the overall efficiency of a gas liquefaction plant by replacing all inline Joule-Thomson expansion valves with cryogenic turbine generators and, as a by-product of this replacement, the cogeneration of electric power. Areas of concern during the development of the generators included optimization of the generator's voltage to maximize system life and efficiency, the impact of high-speed switching IGBTs on wire and ground insulation, the magnitude and effects of partial discharge in a cryogenic liquid environment and the compatibility of insulation materials to hydrocarbon based fluids at cryogenic temperatures View full abstract»

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  • Quality assurance of generator and motor insulation system

    Page(s): 512 - 515
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (364 KB)  

    Dielectric testing is part of quality assurance and preventative maintenance programs. It helps to determine the actual condition of rotating machine insulation and its components. Testing allows users a way to prevent losses due to unforeseen/undetected faults. Dielectric tests can verify the efficiency of corrective measures such as cleaning and drying procedures as well as repair measures. Dielectric testing includes, dielectric response analysis, loss factor and capacitance measurement, harmonic loss quantity analysis and partial discharge pattern recording View full abstract»

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  • Multiple stress aging of magnet wire by high frequency voltage pulses and high temperatures

    Page(s): 157 - 160
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    This paper presents the results of multistress accelerated aging tests conducted on electrical insulation of fine gauge magnet wire used in high voltage coils of encapsulated flyback transformers. The aim of this work is to find an empirical electrical-thermal model to estimate the lifetime of the insulation exposed to multistress conditions including voltage and temperature at different high pulsating frequencies. The lifetime model was obtained by combining the Weibull distribution of failure data with electrical-thermal multistress aging model. The arbitrary parameters of the combined Weibull-life-stress model were obtained by maximum likelihood estimation View full abstract»

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  • Space charge and field distributions in low-density polyethylene

    Page(s): 493 - 496
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (244 KB)  

    The space charge distributions in LDPE (low-density polyethylene) were measured by PEA (pulsed electro-acoustic) method, We used two kinds of LDPEs: m-LDPE polymerized with metallocene catalyst and LDPE polymerized under high-pressure process. The space charge in these two samples strongly depended upon the material of electrode. Semicon electrode enhanced carrier injection into LDPEs. The measurements of space charge dynamics revealed the effective mobility of positive and negative carriers. The space charge was much more stable in m-LDPE than in LDPE View full abstract»

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  • Influence of processing parameters on electrical insulation properties for epoxy-resin materials-an investigation by experiment and finite element analysis simulation

    Page(s): 48 - 51
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    This paper discusses the influence of the speed of the heating process upon epoxy casting of special test specimens on generating mechanical stresses inside a mold. Higher speed leads to higher temperature gradients and therefore to larger internal stresses which by itself promotes cracking in the solid epoxy material. As a consequence of that, the partial discharge inception voltage is decreased. Finite element analysis shows that differences in the thermal expansion coefficient of the materials in the mold together with the absolute temperature level are responsible far the degree of mechanical stresses and finally for the partial discharge behavior of the solid product View full abstract»

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  • A neural network used for PD pattern recognition in large turbine generators with genetic algorithm

    Page(s): 1 - 4
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (300 KB)  

    The paper introduces a new neural network with a genetic algorithm for use in on-line partial discharge (PD) monitoring of large turbine generators. The disadvantages of the BP algorithm which is generally used for PD pattern recognition are discussed. As a result of these shortcomings, a new neural network is presented using a genetic algorithm. To ensure the suitability of the chosen network for PD recognition, the PD patterns which generally occur in large generators were simulated and tested. Test results show that the new neural network can meet the need of PD pattern recognition in large generators satisfactory View full abstract»

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  • An experimental approach to the estimation of the long term corona performance of non-ceramic insulator housings

    Page(s): 193 - 196
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    This paper presents the results from a study on the synergistic effects of corona, humidity and mechanical stresses on the degradation of non-ceramic insulator (NCI) housing materials. Three different polymer formulations, namely silicone rubber (SIR), ethylene propylene diene monomer (EPDM) and a mixture of both were evaluated in a test cell and the surface changes resulting from degradation were monitored. Under the experimental conditions adopted in this study, varying degrees of polymer degradation were observed for each material group. A strong influence of humidity on the development of degradation processes was identified. By computing cumulative charge magnitudes up to the time when surface cracking was detected, a simplistic correlation with expected field operating conditions seems to indicate that even under severe circumstances (corona continuously impinging at the same site) degradation similar to that observed in this unlikely to occur for field exposure times amounting to many years View full abstract»

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  • Comparative aging characteristics of oil-impregnated-paper bushings of different thicknesses subjected to switching surges

    Page(s): 465 - 468
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    Partial discharge tests of oil-impregnated paper capacitor bushings, subjected to voltage switching surges, indicated that overstressed solid-liquid insulation may recover following an electrical stress-free period. However to ensure long term performance of the insulating system, the elevated stresses arising from the superimposed voltage switching surges must be reduced by an increase in the insulation thickness View full abstract»

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  • Dielectric characteristics of capacitors for SF6 insulated switchgear systems

    Page(s): 93 - 96
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    The trend to SF6 insulation technology necessitated the development of capacitors with SF6 as the impregnant. A capacitor dielectric of this nature is presented in this report. Its practical application in an oil-free SF6 grading capacitor is described View full abstract»

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  • A new protection and monitoring system for dry type transformers based on innovative sensor technologies

    Page(s): 255 - 258
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    In this contribution a new protection and monitoring system for dry type transformers is introduced, which consists of three parts and is based on innovative sensor technologies. The first part protects the device against overheating using an optical fibre sensor, which signals an alarm when a local overheating appears. In this case a second unit allows the identification of interturn short circuits in the coils by determining and analyzing the transfer function. The third part, which operates independently from the two others, monitors the partial discharge activity and provides the capability for a localization of partial discharge sources. The developed monitoring system operates online, is efficient and cost-effective and can be easily installed at almost all categories of dry type transformers View full abstract»

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  • Preliminary results on the effect of an inverter environment on coated and uncoated MW35 twisted pair wires

    Page(s): 222 - 226
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    Information is continuously being develop and published on how inverter grade wire will extend the life of electric motors that are exposed to high voltage and frequency pulses. Undertaken in this study is the effect inverter pulses have on MW35 type magnet wire coated with filled and unfilled impregnants, and how humidity might effect life. Presented and discussed is the new data generated as part of this research program, and preliminary explanations are provided for the unusually high aging rates observed, and maybe other possible failure mechanisms View full abstract»

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  • Analysis of partial discharge patterns from a rod to plane arrangement

    Page(s): 439 - 443
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    Partial discharges (PDs) in high-voltage insulating systems may originate from various defects. It is important to identify the type of these insulation defects for instance internal discharges, surface discharges, corona, etc. In the past decade, PD identification research work has been carried out in a way of extracting fingerprints mainly from Phase Resolved and/or PD Magnitude Resolved distribution patterns. Generally, a PD process can be treated as a stochastic process consisting of short duration discharges and charge carrier drift/recombination intervals between these discharges. However, the complexity of PD process makes it difficult to link the PD stochastic process and the measured distribution pattern. The proposed approach yields possibilities for the interpretation of PD physical process using Voltage Resolved PD distribution (VRPD) patterns. Features of VRPD can be computed from the measurable quantities and the information about the discharge physics can be analytically obtained from calculated parameters View full abstract»

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  • Development of knowledge rules for RVM for interpretation of the condition of transformer insulation

    Page(s): 267 - 270
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (260 KB)  

    This paper describes the development of knowledge rules for the interpretation of Recovery Voltage Measurements (RVM) towards the ageing condition of oil-paper insulation. This method measures the polarization behaviour of the insulation. Paper insulated wire, as used in power transformers, is aged under controlled conditions. On the basis of this experiment as well as on basis of field tests on power transformers, knowledge rules are developed to support condition based maintenance of power transformers View full abstract»

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  • A novel, compact instrument for the measurement and evaluation of relaxation currents conceived for on-site diagnosis of electric power apparatus

    Page(s): 161 - 167
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (752 KB)  

    Ageing of insulation materials and systems may well be detected by quantitative measurements of their dielectric response. Such measurements can be performed in the frequency or time domain. In this contribution, a novel type of equipment based on relaxation current measurements is introduced which is designed for on-site tests of high voltage power apparatus. The introduction outlines the reasons for the development. Then, the technique of the instrument is briefly explained. Finally, some examples of on-site measurements on power transformers are presented and post-processing and interpretation of the results is demonstrated View full abstract»

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  • A quicker and reliable screening method for thermal classification of insulating materials

    Page(s): 70 - 72
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    Correct knowledge of the thermal class of insulating materials is very important for efficient and optimal application in electrical equipment. Methods recommended in specifications (e.g. IEC-216) for evaluation of the thermal class need a long duration of about ten months. Often it is not convenient to wait for such a long period. Furthermore the specified method also requires a large quantity of energy, man hours and samples, and is expensive. Therefore, there is a need to develop a quicker but reliable method which at least can be used for screening purposes. This will enable the insulating material manufacturer to develop better material in a shorter time and users to identify appropriate material among a variety of insulating materials available on the market. The advent of modern analytical tools e.g. Thermogravimetric analysis (TGA) provides an appropriate tool in this regard, Several attempts hare been made in this direction. The three major approaches namely, DiCerbo, TPS and Toop methods have some limitations. In the proposed procedure an attempt has been made to overcome previous short comings. This method suggests that activation energy only in the degradation zone shall be considered for the evaluation. The observed results have shown good correlation with data observed from conventional method View full abstract»

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  • Influence of the filler on the breakdown and partial discharge behavior of heat-resistant cast resins

    Page(s): 176 - 179
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    This paper reports on experimental investigations dealing with the influence of the filler on the breakdown and the partial discharge behavior of different cast resin systems. The tests were carried out with a heat-resistant epoxy and a polyurethane resin system in combination with different mineral fillers. The breakdown strength of the insulating materials was measured as a function of the temperature in a uniform as well as in a highly non-uniform electrical field. Additionally the partial discharge inception voltage (PDIV) was determined by using a highly non-uniform electrode arrangement. The contribution reveals that the wollastonite filled epoxy resin shows a worse electrical strength than the corresponding silica filled material. Furthermore it will be displayed that mechanical stresses can have a significant impact on the electrical behavior of cast resins. The experiments with a silica filled epoxy isocyanurate system show that this material has lower breakdown and partial discharge inception voltages but a better temperature stability compared to the corresponding epoxy system View full abstract»

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  • Power transformer monitoring using UHF sensors: installation and testing

    Page(s): 373 - 376
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    External UHF couplers have been fitted to a 1000 MVA autotransformer as part of a project aimed at developing new transformer monitoring techniques. The couplers will supply valuable raw data from a transformer operating under normal service conditions. UHF signals were recorded while the transformer was re-energized and returned to load. Initially, some large discharges appeared, but these were short-lived. Background signal levels were low, indicating no significant interference problems. A small intermittent discharge signal was recorded and its characteristics are described. The possibilities for UHF monitoring of transformers are discussed, together with some of the remaining challenges View full abstract»

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  • An update on silicone transformer fluid: specification, manufacturing, maintenance and end of life options

    Page(s): 412 - 416
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    Silicone transformer fluid has been used in liquid transformers for over 25 years now. There are well over 100,000 silicone fluid filled transformers in operation around the world in network, secondary unit substation, medium power, three phase pad mount distribution and specialty applications. This paper will review recent developments related to the use of the fluid including application testing, manufacturing issues, maintenance procedures, and end of life options. Emphasis is on recent progress within the IEEE Transformers Committee on Dissolved Gas Analysis for silicone filled transformers, a review of environmental characteristics of silicone fluids, and practices of reuse and recycling the fluid View full abstract»

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