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The 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.

Radial field, medium voltage cables operated at 6.6 kV are the object of this study. Dielectric properties of those aged PVC insulated cables have been measured as a function of temperature and voltage in a frequency range of 1 mHz to 1 kHz. The range of temperature tested was between 30°C to 110°. The dielectric material shows a resistive behavior at low frequency. Deduced conductivities are in good agreement with DC conductivities measured at the considered temperatures. The conductivity follows an Arrhenius law over the range studied with an activation energy of 0.96 eV. The conductivity of some sample is high enough to induce an increase of the losses at industrial frequency. The increase of the low frequency capacity is revealing an interfacial polarization. This increase of capacity is due to local accumulation of electric charges in the insulation, particularly at the electrodes. Physicochemical characterizations have been done to understand this decrease of resistivity. A migration of plasticizers did not occur as evidenced by IR micro-spectroscopy. Therefore, the decrease of resistance cannot be attributed to such mechanism. Physical aging is evidenced by DSC, which leads to the working temperature of the cables. TMA has shown modifications of thermo-mechanical properties along aging. These evolutions are attributed to the formation of double bonds resulting from dehydrochlorination.