Modelling and characterization of low-power current transformers for the challenges of modern power networks

This doctoral thesis presents the main activities and results obtained over three years of research dedicated to the development and validation of novel, simplified, and cost-effective metrological characterization procedures for Medium Voltage (MV) Low-Power Current Transformers (LPCTs). In recent years, the widespread installation of switching power converters has increased harmonic injection in modern smart grids, thereby reducing power quality (PQ). While legacy inductive instrument transformers (ITs) often fail to monitor PQ accurately, Low-Power Current Transformers (LPITs) offer a promising solution due to several advantages, including a superior linear frequency response. However, LPITs remain sensitive to external quantities such as temperature and electromagnetic fields. Consequently, this research addresses the challenge of accurately measuring the frequency response of LPITs within the PQ frequency range under predefined operating conditions. The proposed techniques target stakeholders ranging from Distribution System Operators (DSOs) to small technical offices, aiming to reduce costs, shorten testing times, and simplify procedures while contributing to the scientific community. The thesis begins with an overview of MV current sensors, relevant standards, and uncertainty calculation methods, and then presents three original contributions focused on Rogowski Coils (RCs). First, a new and straightforward method for obtaining the frequency model of commercial RCs using datasheet inputs is validated through simulation and laboratory tests. Second, the output variability of identical RCs under consistent conditions is investigated. Finally, a simplified characterization procedure for the frequency response of RCs is developed, and its results are compared with those obtained using the traditional method.