Tree growth monitoring by means of digital partial discharge measurements

In this work results relevant to electrical treeing tests performed on several ethylvinylacetate EVA (with different vinylacetate percentage) and on cross linked polyethylene (XLPE) (of two different lots) polymer materials are presented. During the tree growth the partial discharges (PDs) were monitored by means of a digital PD acquisition system and the tree morphologies were optically evidenced by means of video recorder equipment. The PD acquired data, the outcome of the video monitoring and the time-to-breakdown were off-line processed and analysed. In this way, two main results were obtained: the first one, applicable to this kind of laboratory treeing tests, is related to the possibility of predicting the lifetime of the specimens, considering a specific PD measurement derived quantity; the second one demonstrates the possibility to detect the tree morphology considering the phase-number distribution obtained by the digital PD measurement. The presented test procedures are deemed to have a potential for diagnostic applications.

I. Introduction

In past years, digital PD measurements performed during aging tests have provided important tools in order to identify both the damage site where PDs take place, and the kind of defect causing the PD inception. The PD data post-processing allows the definition of statistical parameters and derived quantities that can be useful in order to obtain information about the results [1]–[4]. In [5] it was demonstrated that data acquired during surface PD tests on polymeric films, using a particular test cell, lead to the identification of derived quantities significant to monitor the degradation phenomenon, whose values change during the aging process.