Detection and Localization of Transient Sources: Comparative Study of Complex-Lag Distribution Concept Versus Wavelets and Spectrogram-Based Methods

International audienceThe detection and localization of transient signals is nowadays a typical point of interest when we consider the multitude of existing transient sources, such as electrical and mechanical systems, underwater environments, audio domain, seismic data, and so forth. In such fields, transients carry out a lot of information. They can correspond to a large amount of phenomena issued from the studied problem and important to analyze (anomalies and perturbations, natural sources, environmental singularities, ...). They usually occur randomly as brief and sudden signals, such as partial discharges in electrical cables and transformers tanks. Therefore, motivated by advanced and accurate analysis, efficient tools of transients detection and localization are of great utility. Higher order statistics, wavelets and spectrogram distributions are well known methods which proved their efficiency to detect and localize transients independently to one another. However, in the case of a signal composed by several transients physically related and with important energy gap between them, the tools previously mentioned could not detect efficiently all the transients of the whole signal. Recently, the generalized complex time distribution concept has been introduced. This distribution offers access to highly concentrated representation of any phase derivative order of a signal. In this paper, we use this improved phase analysis tool to define a new concept to detect and localize dependant transients taking regard to the phase break they cause and not their amplitude. ROC curves are calculated to analyze and compare the performances of the proposed methods

Analyse diélectrique en tension et température de câbles à isolation PVC après exploitation

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Dielectric and physicochemical behavior of aged PVC insulated cables

International audienc

Determination of the aging mechanism of single core cables with PVC insulation

International audienceTwo set of single core cables with PVC insulation with different decreases of electrical resistivity have been analyzed to determine the aging mechanism responsible for this decrease of electrical properties. Four different aging mechanisms can be considered: oxidation, effect of water ingress, loss or migration of plasticizers and dehydrochlorination. IR spectroscopy has not revealed any oxidation nor the presence or the effect of water. IR microspectroscopy has confirmed the uniform composition of the polymer throughout the sample. SEM and EDX analyses have highlighted clusters of lead chloride. The presence of this compound results from the reaction of the thermal stabilizer due to the mechanism of dehydrochlorination. However, these techniques did not distinguish between the two samples of different resistivity. UV spectroscopy revealed the presence of double bonds in the two samples and show that the concentration is higher in the cable with the worse electrical properties. The formation of double bonds is a consequence of the dehydrochlorination and cannot result from one of the three other aging mechanisms considered. Although the measurement of chloride ion concentrations by coulometry should have confirmed this aging mechanism, the surprisingly low measured levels of chloride ions are discussed with regards to the adequacy of the method to measure lead chloride in cluster forms

Analysis of the resistivity loss of aged PVC cables and effects on their dielectric strength

International audienc

Physicochemical behavior of aged PVC insulated cables

International audienc