The science of electric arc extinction in high voltage direct current transmission

The primary focus of this doctoral research has been on High Voltage Direct Current (HVDC) systems, particularly on the analysis and mitigation of transient faults in Voltage Source Converter (VSC) systems equipped with Direct Current (DC) breakers. This work has been motivated by the need to improve the stability and availability of HVDC links, especially in systems with overhead lines that are prone to transient faults. A key aspect of the research has been the estimation of arc extinction times for pole-to-ground faults, which is essential for optimizing the dead times required for successful line reclosing in VSC systems with mixed cable-overhead lines. This research has been documented in [1]. Another crucial area of investigation has been the mutual electromagnetic induction effects between hybrid AC/DC transmission lines, particularly under fault conditions. This part of the work provides insights into harmonic interference between the AC and DC circuits, which is a crucial consideration for the performance of hybrid transmission systems. This work was published in the article [2]. Finally, a review of recent trends in HVDC modeling has been conducted, placing this research within the broader context of modern power system developments and underscoring the growing significance of HVDC systems in the evolution of modern power grids. This review has been published in the article [3]. In parallel to the primary focus on HVDC systems, three additional studies were conducted that, while not directly related to HVDC technology, address important challenges in modern power systems. First, the research on arc extinction was also extended to Extra-High Voltage (EHV) Alternating Current (AC) systems, particularly focusing on the single-pole autoreclosure (SPAR) process in uncompensated mixed cable-overhead lines. Time-domain simulations were employed to demonstrate how transient fault extinction times in these systems are affected by the presence of a small cable stretch, offering valuable insights for improving SPAR performance. These findings were published in the article [4]. The second of these studies investigated transient overvoltages in Medium Voltage (MV) distribution networks, proposing a simplified method based on the Clarke transform for evaluating these phenomena. This method has provided a significant reduction in computational complexity while maintaining accuracy, making it a practical tool for assessing overvoltage risks in MV networks. This work was published in the article [5]. The third study addressed evolving reactive power and voltage stability challenges in urban distribution and subtransmission networks. Changes in the electrical system, such as the decrease in inductive reactive power absorption due to modern appliances and the increased use of cable lines in urban environments, were analyzed, and potential solutions, such as the installation of shunt reactors, were proposed. The findings from this research were published in the article [6].