WIRELESS DETECTION OF PD PATTERNS: APPLICATIONS IN SMART GRIDS AND MODERN POWER SYSTEMS

In this thesis, different challenges for various applications of a wireless PD detection instrument are discussed and relevant solutions are proposed. The main purpose is to assess the applicability of such technology both in current HV and MV power systems as well as in future applications for smart grids. The main challenges for these types of diagnostic systems are the following: • voltage synchronization of Phase Resolved PD pattern; • PD recognition under non-sinusoidal voltage waveforms; • PD recognition under sinusoidal voltage superimposed harmonics; • PD recognition in laboratory and in real world situations under noise and other source of disturbance. Thanks to the collaboration with Terna, it was possible to carry out several analysis and experimental measurements on HV transmission lines to assess the problems that may be arise when PD measurements is carried out without access to the local voltage signal. In this case, the voltage signal can be taken from a remote location where access to voltage measurement is possible and the voltage phase-shift caused by the operating transmission line must be assessed. In the second part of the study, the problems arising from PD measurements performed in non-sinusoidal regime to recreate the stresses that may be present in future networks following the presence of AC/DC conversion systems. This topic was addressed thanks to the collaboration with Chalmers University of technology in Gothenburg, SE. A Further investigation on superimposed harmonic voltage effects on PD measurements has been discussed. The aim of this research was to understand and evaluate the impact of harmonics on partial discharge behaviour, in particular on the PD measurements by means the Pry-Cam portable instrument, and on the PD Pattern acquisition process. The results showed that various harmonic, 3rd, 5th, 9th and 11th superimposed on the fundamental sinusoidal waveform have a significant impact on PD amplitude and PD pattern shapes. The presence of harmonics components can significantly influence the acquisition of the PD pattern and also may arise synchronism problems during the measurements. In order to assess the capability of the portable instruments of detecting the precise location of the PDs, different comparative tests have been carried out performing measures both with standard fixed PD measurement system as well as with the portable one. Depth investigation of peculiar experimental cases carried out at the High Voltage Laboratory of Prysmian S.p.a. in Milan (Italy) on a MV and an HV cable are described. To complete this part, a wide description of several exemplary measurements carried out with a portable instrument (Pry-Cam) in several sites is here given. Measures were carried out in Medium and High voltage networks. In detail, it was possible to analyze various noise phenomena and the methodologies, used for correctly assessing the phenomenon under study, are described. Thanks to Prysmian Electronics, it was possible to perform PD measurements in several European and Extra-European countries during HV testing for commissioning of new cable interconnections at different voltage levels. In addition, the study was also extended to the analysis of PD phenomena in MV distribution networks present in the Sicilian territory. The study gave the opportunity to investigate the main problems encountered in cable lines and MV accessories. In this case, it was also possible to conduct a study on the correlation of ozone levels and the PD sources in MV cabins.