In this work, we study the effect of the applied voltage form and its rise speed on breakdown voltage of polyvinyl chloride sheaths. We first present the statistical model of Weibull used for processing the results, then we describe the experimental devices. We finally study the evolution of the nominal breakdown voltage with 8 different rise ramps up to 4.75 kV.s -1 and under different forms (AC 50 Hz, positive and negative DC voltage). A population of 50 samples has been used for calculating the mean breakdown field at each profile voltage.

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Several techniques exist to characterize the presence of remanent polarization and / or space charge in an insulating material. Among them which may be mentioned thermal methods such as the Thermal Wave Method (TWM). Among the most widely used polymers in electrical insulation, we find the polychloride vinyl (PVC). In this work, we describe the characterization of PVC sheaths to improving the reliability of power transmission cables. We set the objective to adapt the TWM for space charges measures in this material and under this cylindrical form. The study concerns a few samples of PVC sheaths, part of which has undergone aging until 4250h under alternating voltage of 20 kV sinusoidal AC voltage in the electrical engineering laboratory of Bejaia (LGEB). Also we have another lot of samples in new condition for comparison. The space charge measurements were made at LUSAC in Cherbourg. After presenting the specific banc measurement of MOT for this type of samples, we present the first current measurements on samples aged under tension between 500 and 4250 hours. The first analyzes show that the current of MOT increase gradually but irregularly depending on the aging time.