M. Conti

University of Bologna, Bologna, Emilia-Romagna, Italy

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Publications (16)2.72 Total impact

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    ABSTRACT: This paper describes a new algorithm for the automatic identification of the type of partial discharge sources in insulation systems of rotating machine stator windings. The proposed algorithm is based on fuzzy rules that associate each partial discharge phenomenon to a fuzzy space class trough a tree path selection. The output is a simple frame where the defect type and a membership are evidenced. Applications of the algorithm to analyze data collected both on field and in laboratory are reported and discussed to show its validity and robustness.
    Electrical Insulation, 2004. Conference Record of the 2004 IEEE International Symposium on; 10/2004
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    ABSTRACT: Partial discharge (PD) measurements constitute one of the most promising tools for electrical insulation diagnosis. This paper describes how a procedure based on PD measurements can provide early detection of electrical trees in polymeric insulation systems. Such an application relies upon a new methodology, which provides enhanced tools for the identification of PD generating defects. Tree inference is carried out stepwise. Acquired signals are primarily separated according to their waveform, thus achieving data sets related to a specific PD typology. Then, fuzzy algorithms are applied to PD height and phase derived quantities belonging to these homogeneous data sets, in order to assign a membership degree to specific output categories. If the data set is relevant to an internal defect, a further analysis is performed in order to establish whether or not this defect is a treed region. The algorithm described in this paper was developed resorting to tests performed on artificial test specimens and electrical apparatus. In particular, the rules to detect the presence of electrical trees were derived from experiments carried out on needle-plane objects, constituted by slabs of cross-linked polyethylene (XLPE) where a needle is inserted and partially extracted in order to generate a cavity in front of the needle tip. Tests were also performed on cables having artificial defects., as well as on other insulation systems, such as high frequency transformers. Applications of the proposed approach to MV cables and to HV transformers show that electrical trees can be detected successfully before final breakdown.
    IEEE Transactions on Dielectrics and Electrical Insulation 09/2004; · 1.36 Impact Factor
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    ABSTRACT: Aim of this paper is to validate the effectiveness of an artificial intelligence technique devised for tree diagnosis in solid insulation systems. For this purpose, electrical and optical partial discharge (PD) measurements were carried out on specimens containing treed regions of different typologies ("bush" and "branch"). The results obtained by the above-mentioned diagnostic procedure were checked on the basis of the tree typology.
    Solid Dielectrics, 2004. ICSD 2004. Proceedings of the 2004 IEEE International Conference on; 08/2004
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    ABSTRACT: Results of a comparison of different methods adopted for electrical tree identification, based on partial discharge measurements, are reported and discussed in this paper. Attention is paid to an analysis of the transition from partial discharges occurring in defects of insulation systems to electrical trees. It is shown that significant information is provided by parameters associated to partial discharge inter-time distribution and phase distribution. This result looks promising to enhance the diagnostic efficiency and the design of CBM procedures.
    Solid Dielectrics, 2004. ICSD 2004. Proceedings of the 2004 IEEE International Conference on; 08/2004
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    ABSTRACT: Partial discharge (PD) analysis is a fundamental tool to guide decision making in electrical insulation diagnosis for condition based maintenance. In this paper, PD signals are analyzed to localize defects in insulation systems. The task of automatic defect localization with respect to electrodes has a wide range of industrial applications. In fact, depending on the apparatus type, risk assessment is remarkably affected by defect location with respect to the electrodes. In this study, various parameters are first extracted from PD distributions, and statistical analysis is performed to select the most significant parameters concerning localization. Then, the localization process is carried out through numerical classification. Three different classification methods are compared to find the best approach for this application. Comparing a k-nearest neighbor classifier, a probabilistic neural network and a support vector machine (SVM) based classifier, the best results are gained with SVM. although the former two are simpler to implement and easier to tune. SVM based classification has not been applied in PD analysis before this research.
    Industrial Electronics, 2004 IEEE International Symposium on; 06/2004
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    ABSTRACT: Partial discharge measurements performed at 0.1, 20, 50 and 300 Hz and at different voltage levels are compared with simulations based on models available in literature. It is shown that these models need to be improved to be able to fully extrapolate PD behavior at different frequencies. A solution based on a time-dependent increase of the work function when detrapping from negative charged surfaces is proposed and verified on the basis of experimental data.
    Electrical Insulation and Dielectric Phenomena, 2003. Annual Report. Conference on; 11/2003
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    ABSTRACT: An investigation on the behavior of partial discharges occurring in insulation cavities as a function of environmental conditions is presented in this paper. In particular, focus is made on peculiar conditions where semi-transparent insulation is subjected to different visible light intensity, is irradiated by UV or is kept in the dark. Experiments are carried out on cells with an artificial defect, obtained producing a spherical void in epoxy resin. It is shown that not only PD inception voltage is sensitive to fight wavelength and intensity, but also PD average delay time changes considerably. It can be speculated that inception voltage can be related prevailingly to either background radiation or field-assisted electron detrapping from defect surfaces, depending on defect geometry and environmental conditions.
    Electrical Insulation and Dielectric Phenomena, 2003. Annual Report. Conference on; 11/2003
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    ABSTRACT: During online partial discharge (PD) measurements on AC rotating machines, one of the noise typologies that affects PD patterns is the so called "cross-talk", that is, discharges that appear in the tested phase as a result of coupling from another phase. An approach to cross-talk recognition, based on PD-pulse shape and phase analysis, is presented in this paper. It is shown that, the signal distortion, due to the different propagation path, can help in separation of PD signals relevant to the main and cross-talk PD patterns. The cross-talk recognition can be achieved applying appropriate phase shift analysis to the separated PD patterns. The rejection of cross-talk patterns can make easier PD source identification and the relevant diagnostic decision can be more reliable.
    Electrical Insulation Conference and Electrical Manufacturing & Coil Winding Technology Conference, 2003. Proceedings; 10/2003
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    ABSTRACT: 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.
    IEEE Transactions on Dielectrics and Electrical Insulation 07/2003; · 1.36 Impact Factor
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    ABSTRACT: This paper presents results of tests having the purpose to derive indexes, from PD measurements, which can enable the recognition of PD generated from different sources, such as internal voids, surface and corona discharges. Moreover, recognition of the location and shape of cavities can be achieved. PD measurements are performed by a digital instrument which allows PD-pulse amplitude, phase and shape to be recorded. Such results can be employed to improve recognition efficiency of PD-based diagnostic tools used for on field applications.
    Electrical Insulation, 2002. Conference Record of the 2002 IEEE International Symposium on; 05/2002
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    ABSTRACT: This paper presents a new identification technique, based on fuzzy logic, which enables the recognition of PD generated from different sources, such as internal, surface and corona discharges. It is shown that the different sources typologies can be identified on the basis of fuzzy rules applied to a selection of parameters derived from PD-pulse phase and amplitude distributions. The proposed procedure is finally applied to rotating machines and cables, with real insulation defects, showing promising on-field applications.
    Electrical Insulation and Dielectric Phenomena, 2002 Annual Report Conference on; 02/2002
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    ABSTRACT: The aim of this paper is to derive PD-based indexes and criteria that are able to indicate whether an internal defect, a cavity, is located close to the HV electrode, to the ground electrode, or in the bulk of the insulation. For this purpose, several measurement sessions were carried out on laboratory samples whose geometry was suitably designed (CIGRE type I and type II cell). In addition, measurements were performed on a capacitive insulator, having known location defects. The measurements results and their evaluation are described in the paper. It is shown that indexes useful for PD source location can be extracted from PD phase distributions.
    Electrical Insulation and Dielectric Phenomena, 2002 Annual Report Conference on; 02/2002
  • Proceedings of IEEE SDEMPED; 09/2001
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    ABSTRACT: The problem of the identification of Partial Discharge (PD) phenomena in electrical apparatus, where the PD signals detected at the measurement bus can be significantly attenuated and distorted by the transmission path, is dealt with. Recently, it has been shown that the shape parameter of the Weibull function, β, can be used to identify PD-source typologies, even in the presence of different PD phenomena simultaneously active. This paper provides further contributions to the validation of β as aging marker, focusing on the behavior of β in the presence of distortion and attenuation of PD signals due to the influence of the transmission path between the detection point and the PD source. For this purpose, different PD sources, such as internal void, surface and corona discharges, were considered in the experiments
    Solid Dielectrics, 2001. ICSD '01. Proceedings of the 2001 IEEE 7th International Conference on; 02/2001
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    ABSTRACT: This paper presents the results of space charge and partial discharge measurements carried out on enameled wires, specifically designed to be used in electrical motors fed by adjustable speed drives. These procedures described can provide a useful tool for short-term evaluation of enameled wires, which can give indications also on long-term performance. Partial discharges and space charge accumulation seem to be significantly influenced by the supply voltage waveform features (frequency and shape), with an extent depending on the material itself. Moreover, partial discharge features, such as pulse height and inception voltage, depend considerably on space charge accumulation which may occur, e.g., with unipolar waveforms. Both techniques provide considerably different fingerprints of the two tested kinds of wires
    Electrical Insulation Conference and Electrical Manufacturing & Coil Winding Conference, 2001. Proceedings; 02/2001
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    ABSTRACT: A new diagnostic tool based on partial discharge (PD) measurements is presented in this paper. Unlike conventional PD detectors, which record PD pulse height, the tool described is based also on the shape of PD pulses. PD pulses are digitised and recorded in fast RAM banks. The diagnostic tool uses a fuzzy interface to separate firstly PD pulses in classes according to their shape, then applies statistical analysis of PD pulse height and phase on the pulses recorded in each class. A fuzzy logic inference engine is then employed to provide indications on the nature of the defects generating PD. In the paper, a short description of the proposed diagnostic tool is presented along with its application to different insulating systems, i.e., cable joints, cables and high frequency transformers
    Electrical Insulation Conference and Electrical Manufacturing & Coil Winding Conference, 2001. Proceedings; 02/2001