Characterization and measurements of partial discharges on polymeric materials for HVDC applications

The aim of this thesis is to provide a comprehensive overview of the Partial Discharge (PD) phenomenon in polymeric materials under DC. To achieve this, we start by conducting tests in AC conditions to identify features and locate the sources of PDs. This initial phase is really important because identifying the origins of PDs becomes exceptionally difficult under DC conditions. Subsequently, the focus shifts to DC tests aimed at understanding similarities to and deviations from the AC phenomenon. The thesis is composed by six chapters, the first five of which offer a complete overview of the PD phenomenon, while the final chapter centers on the conducted tests. The opening chapter outlines the fundamental differences between polymeric materials operating under AC and DC conditions, underlining phenomena like the space charge effect. Moving forward, the second chapter explain the characteristics of polymeric materials, elucidating their primary features and different conduction mechanisms. The third chapter explores PD physics, providing an overview of various discharge types, with a predominant focus on internal discharges, which pose greater risks to insulators. The fourth chapter explain the PD measurements methods, the different sensors that are used and also a brief mention on the noise rejection method that is commonly used. Chapter five addresses the Partial Discharge phenomenon under DC conditions, including the latest identification methods for PDs. The final chapter synthesizes the PD measurements and insights acquired from tests conducted under both AC and DC conditions. Additionally, it presents a comparative analysis of the PD phenomenon in AC versus DC scenarios. This thesis comprehensively covers the spectrum of Partial Discharge phenomenon in polymeric materials under both AC and DC conditions, elucidating key aspects, measurement methodologies, and comparative analyses between the two operational modes.