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Electrical Insulation, IEEE Transactions on

Issue 6 • Date Dec 1993

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Displaying Results 1 - 20 of 20
  • Measuring the endurance of films in partial discharges

    Page(s): 1050 - 1056
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    A new test assembly for measuring the endurance of polymeric and ceramic films under the action of partial discharges (PDs) is presented. If experiments are performed under controlled ambient conditions (i.e., relative humidity), the test procedure gives times to breakdown which show low scatter. The effects of different test conditions on the times to breakdown and relevant data scatter are presented. The adoption of a phase reference PD analyzer (PRPDA) system, together with a video recording system, also gives information relevant to discharge mechanisms and film degradation processes. The test assembly is described and some results, relevant to polymeric films of different thickness, are presented View full abstract»

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  • The definitions used for partial discharge phenomena

    Page(s): 1075 - 1081
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    A variety of definitions related to partial discharge (PD) phenomena are discussed. There is no general agreement at this time of writing as to the definitions of the various regimes of PD. A certain confusion exists which may be due to the multitude of PD manifestations. An attempt is made to elucidate some aspects of the PD definitions. Related problems needing more work are noted View full abstract»

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  • Present state and prospects of standardization on PD measurements

    Page(s): 902 - 904
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    The contents of the past and present IEC Standards on partial discharge (PD) measurements are examined, in view of the preparation of a new edition. New standards should take into account the more sophisticated measuring systems produced in the last decades and their lower sensitivity to external disturbances. Little knowledge has however been added on the PD aging effects on HV apparatus View full abstract»

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  • Neural networks as a tool for recognition of partial discharges

    Page(s): 984 - 1001
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    The application of three different neural networks (NNs) to the recognition of partial discharge (PD) is studied. Results of PD measurements on simple two-electrode models, as well as on models of artificial defects in industrial objects, are presented. The PDs are measured using conventional discharge detection, and PD patterns are processed by previously developed statistical tools. Mathematical descriptors are used as input patterns for a backpropagation network, Kohonen self-organizing map, and learning vector quantization network. All three NNs recognize fairly well the PD patterns of those insulation defects for which they were trained. On the other hand, the NNs could misclassify those PD patterns for which they were not trained. The classification of PD patterns by NNs can be influenced also by the structure of the particular NN, the value of the convergence criterion, and the number of learning cycles View full abstract»

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  • PD pattern recognition with neural networks using the multilayer perceptron technique

    Page(s): 1082 - 1089
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    The partial discharge (PD) pattern recognition capability of a neural network, employing the multilayer perceptron technique with data input based on five discharge pulse form parameters, is examined. Simple discharge sources, consisting of artificially created cylindrical cavities with metallic and dielectric electrodes, are employed. The PD pattern discrimination capability is tested using cavities of equal depth but with different electrodes, and cavities of varying depths but with similar electrodes. Preliminary test results are positive View full abstract»

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  • The effect of the definition used in measuring partial discharge inception voltages

    Page(s): 1002 - 1006
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    At present, several definitions of partial discharge inception voltage (PDIV) have been advanced. To establish the value of each of these definitions, four practical electrical insulating fluids are selected, and their PDIV is determined according to three of these different specifications. The results suggest that the use of PDIV as a quality criterion generally is not warranted. The significance of these findings is discussed View full abstract»

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  • Partial discharge measurements in dielectric liquids under impulse voltage

    Page(s): 947 - 955
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    Current pulses caused by partial discharges (PDs) are measured using light-emitting diodes (LEDs) and fiber optics under impulse voltage conditions. This system has the advantage of having good isolation from the HV power supply and no effect from electromagnetic noise as compared with ordinary systems. It can detect a PD pulse having a half width of 3 ns, and has the capability of measuring PD pulse charges in the range of 1 to 2000 pC, when the optimum DC bias is applied. PD pulses and light emission or streamer formation in dielectric liquids are measured simultaneously by using an image converter camera View full abstract»

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  • Partial discharge measurements using tailored excitation waveforms

    Page(s): 1068 - 1074
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    This paper proposes that the injection of an impulse, at a suitable time on a power frequency voltage wave, can trigger the inception of partial discharges. In this way a deterministic component is introduced into the observation of partial discharge activity and the ability to minimize the influence of noise in a measurement is enhanced considerably. Two simple experiments are described which demonstrate the triggered inception of partial discharges and the strong `focusing' effect of the triggering impulse, whereby the discharge activity is concentrated immediately after the injection of the impulse and a significant `quiet' period follows in which minimal discharge activity occurs View full abstract»

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  • Pulse height analysis of partial discharges in air

    Page(s): 932 - 940
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    The pulse height distribution (PHD) functions of partial discharges (PDs) generated by AC voltage in air are investigated. The electrode systems used allow the investigation of single-source PDs and/or multiple-source discharges. Because voltage and the electrode configuration alter the PHD functions of even a single PD source, the overall effect of voltage an multiple-source discharges is rather complicated. The results indicate that the PHD functions of the multiple-source discharges are the superposition of the distribution functions of the discharges and the component sources acting alone. Knowledge of the PHD functions of the typical PD sources together with some kind of deconvolution technique could help in interpreting the results of PD measurements performed on more complex, real insulation systems and, perhaps, identify the main sources of PD in those systems View full abstract»

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  • Detection and location of internal defects in the insulation of power transformers

    Page(s): 1057 - 1067
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    With the development of fast, and low-cost analog-digital converters (ADCs) and new mathematical procedures for waveform description, e.g., time encoded signal processing and recognition (TESPAR), novel approaches to detect and locate internal defects in the insulation of power transformers become feasible if the following requirements are fulfilled: the equivalent circuit of the insulating system, suitable for the fast partial discharge (PD) signals with risetimes of ~10 ns, is known; the response of the insulating system to PD signals injected at least at three different sites of each winding (top, center, bottom) is calculated, or measured at the signal tap-off points (i.e., bushings); and the pattern matrix of all calculated or measured signals exists: e.g., encoded and signal processes with TESPAR as a reference. The above mentioned requirements are examined for quasi-simultaneous detection and location of internal defects in power transformers. The method is applied to PD measurements on power transformers View full abstract»

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  • The relation between thermal and electrical stress and the PD behavior of epoxy-resin transformers

    Page(s): 1007 - 1015
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    The partial discharge (PD) behavior of epoxy resin transformer coils in a temperature range between -30 and 180°C is discussed. In particular, the PD inception voltage, which is a very important parameter for the judgement of the PD characteristic of a transformer over the temperature range, is considered. The PD inception voltage is determined at different static temperatures in step tests. The tempering of the coils occurs from the outside by submerging the oil in tempered fluid,as well as from the inside, with the help of current losses. Models of HV coils of distribution transformers are used as specimens. The dependencies between the PD inception voltage of the coils and parameters such as wire insulation and inner or outer tempering are determined and discussed. The results of long-term tests in which five coils are stressed with a voltage of 1.75 kV at a temperature of 175°C for a duration of one year are presented. During this time PD measurements with a sensitivity of 2 pC were carried out View full abstract»

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  • A critique of present calibration procedures for partial discharge measurements

    Page(s): 1043 - 1049
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    The need for improved standardization procedures for use on different types of partial discharge (PD) measuring systems is discussed. This requirement is examined using recording and processing data of complex PD signals obtained from in-service electrical apparatus. It is concluded that more fundamental knowledge of the PD mechanisms must be gained before any significant changes in existing calibration procedures can be made View full abstract»

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  • Classification of partial discharges

    Page(s): 917 - 931
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    For a long time, classification of partial discharges was performed by eye, by studying discharge patterns at the ellipse of an oscilloscope screen. The introduction of digital processing techniques allowed automation of the recognition procedure. These procedures are reported and applied to a number of actual HV constructions which suffer from partial discharges. The results of these tests show that a quite satisfactory recognition of discharges takes place View full abstract»

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  • On the character of different forms of partial discharge and their related terminologies

    Page(s): 956 - 968
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    Experimentally obtained partial discharge pulse forms are compared with those derived theoretically, using a mathematical model of a short gap. The calculations indicate that, with overvolted short gaps, the apparent absence of the protracted ion current tail in the overall pulse form is due to the large excess of the electron current component generated by strongly enhanced cathode emission by the photoeffect and other phenomena. Under conditions of high overvoltage the ion-impact-induced emission, the ion fluxes and, consequently, the ion current component are greatly reduced as compared to the electron current. The long ion current tail, representing not more than a few percent of the total current, passes undetected. Pulseless and pseudo-glow discharges are considered. Preferred terms to designate the different forms of partial discharges are suggested View full abstract»

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  • Computer-aided measurement of partial discharges in HV equipment

    Page(s): 969 - 983
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    A previously developed method of partial discharge (PD) recognition is used to evaluate PD in HV devices. Using conventional discharge detection (bandwidth ~400 kHz), the PD patterns are studied. By means of unambiguous statistical operators like skewness, kurtosis, number of peaks, etc., quantitative information about the discharge source can be obtained. In the case of an unknown defect, a combination of these operators is compared to the same set of operators for a known configuration. In this way, a statement can be made on the character of a discharge source. The use of this technique in evaluating different discharges in HV cable and in 400 kV SF6 insulation confirms the usefulness of the new approach View full abstract»

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  • Digital measurement of partial discharges in full-sized power capacitors

    Page(s): 1025 - 1032
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    Partial discharges measurements in power capacitors have been carried out using a digital technique. The advantages of the use of this digital technique are discussed. The digital equipment design is presented. Test results on industrial all-film power capacitors with high capacitance values are presented together with measurements of the PDIV before and after the endurance tests View full abstract»

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  • Importance of unraveling memory propagation effects in interpreting data on partial discharge statistics

    Page(s): 905 - 916
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    The significance of memory propagation in controlling the stochastic behavior of partial-discharge phenomena is demonstrated by determination of various conditional amplitude and phase-of-occurrence distributions for both measured and simulated discharge pulses. A system that can be used to measure directly a set of both conditional and unconditional pulse amplitude and phase distributions needed to reveal memory effects and quantify the phase-resolved stochastic properties of partial-discharge pulses, is briefly described. It is argued that not only is an unraveling of memory effects essential in any attempt to understand the physical basis for the observed stochastic behavior of partial-discharge phenomena, but also that the data on conditional distributions provide additional statistical information that may be needed to optimize the reliability of partial-discharge pattern recognition schemes now being considered for use in insulation testing View full abstract»

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  • Partial discharges and streamers in liquid dielectrics-the significance of the inception voltage

    Page(s): 941 - 946
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    Recent studies have determined the partial discharge inception voltage (PDIV) of several practical insulating oils using conventional PD measurements. They show that the PDIV is a reasonably reproducible quantity. Independently, using electrooptical techniques, the streamer inception voltages (SIVs) in these liquids have been measured. These SIV values are found to be reproducible, within experimental error. Both techniques yield similar inception values. These results suggest that the PD and streamer phenomena are closely related. It is shown that the PDIV is independent of the gap and hence the average electric field. The SIV is found to be independent of the applied voltage. These observations suggest that the inception of both phenomena is controlled by the local rather than the average applied field. The experimental observations are interpreted and a theory is advanced to explain them View full abstract»

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  • Diagnosis of partial discharge signals using neural networks and minimum distance classification

    Page(s): 1016 - 1024
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    Two different methods for classifying partial discharge (PD) phenomena by a personal-computer-aided system are described. The first is concerned with common minimum distance classification, using statistical data on pulse quantities such as apparent charge, energy and phase. Applying the correct algorithms and features, such a system is able to discriminate between unknown defects using conventional discharge patterns. Classification with neural networks, which offers the possibility of classifying the shape of the PD pulses without using statistical tools for data reduction, is also discussed. Examples of diagnostic decisions are shown for a gas-insulated-switchgear system with several artificially introduced defects. The reliability of the diagnosis is estimated for both time-resolved detection evaluated by neural networks and classic phase-resolved PD evaluation. A two-step strategy of time-resolved preclassification and automated phase-resolved evaluation is introduced View full abstract»

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  • PD analysis of rotating AC machines

    Page(s): 1033 - 1042
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    The problem of the interpretation of partial discharge (PD) measurements is approached by means of the shape analysis of PD amplitude distributions. Experimental cumulative PD distributions, detected insulation systems of HV rotating machine stator windings, are plotted on a Weibull graph in order to identify multiple PD sources. Examples of the application of PD distribution shape analysis as a diagnostic tool for AC HV stator insulation systems are presented and discussed. The calibration procedure and the significance of average parameters for degradation inference are reviewed View full abstract»

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Aims & Scope

This Transactions ceased production in 1993. The current retitled publication is  IEEE Transactions on Dielectrics and Electrical Insulation.

Full Aims & Scope