The increasing integration of renewable energy sources and power electronic devices is changing the electricity grid, leading to widespread harmonic and supraharmonic distortions. Accurate measurement and calibration of current transformers (CTs) up to the 150 kHz range are essential for reliable power quality assessment and grid monitoring. However, traditional calibration approaches are limited in both bandwidth and practicality, particularly for high-current and high-frequency conditions.

This thesis develops and validates a broadband calibration methodology for CTs, enabling ratio and phase error characterization from 50 Hz to 150 kHz using a high-precision digital sampling ammeter (from a power analyser) as the core measurement instrument. The proposed system eliminates the need for auxiliary equipment and thus reduces component count, ultimately allowing for simplified broadband calibrations. An uncertainty budget is established with combined expanded uncertainties (k=2) for the measurement system of less than 10 ppm up to 10 kHz, and less than 100 ppm at 150 kHz for the secondary-to-secondary comparison method. This is an improvement over the previous state of the art for this setup, which had an uncertainty of 50 ppm and a maximum frequency of 10 kHz. For primary-to-secondary calibration, uncertainties remain below 110 ppm at the highest frequency, allowing for the further development of a reference current transformer.

The thesis systematically examines the influence of critical experimental factors, such as grounding configuration, shunt selection, conductor positioning, cabling, and measurement duration, on overall calibration accuracy and repeatability. Key findings include the importance of instrument warm-up, the impact of earth-loop currents, and practical considerations for shunt and cable selection for high-frequency application. The demonstrated approach provides a metrological foundation for future implementation of wideband CT accuracy classes and supports ongoing international efforts to establish traceable measurement infrastructure for power quality applications.

This work, carried out at the Dutch national metrology institute (VSL), aims to contribute to the goals of the European ADMIT project.

Today, 60% of the European mainline railway network is electrified with 80% of total traffic. It will further increase driven by The Trans-European Transport Network (TEN-T) and sustainability initiatives. As electricity consumption by railway networks increases, quantification of rail transport’s actual energy consumption is essential. Currently, railways’ energy consumption is measured at the supply side, i.e., the grid, which includes the network’s losses. This measurement does not give actual energy consumption. The European Union demanded an on-board energy measurement system for railways from 2019 onward.

The existing energy measurement systems designed for transmission and distribution networks are not suitable for railway applications due to the harsh conditions. The voltage and current signals are highly distorted and need a more sophisticated measurement system. The energy measurement can be divided into current measurement, voltage measurement, and energy calculation. This thesis project is part of the ongoing research in the current measurement for the on-board energy measurement system focusing on the DC current measurement.

The primary objective is to measure the energy dissipated during braking of the train. Therefore, we need to measure the current flowing through the braking rheostat during the braking of the train. This current measurement is difficult due to the fast switching of high current (in order of 500 A-600 A) termed as chopped current.

VSL has developed a test setup to measure the chopped current flowing through the braking rheostat. The test setup is modified to eliminate distortions and achieve the project requirement of 600 A current measurement. Intermediate tests are performed during the modification to analyze the components’ performance. Finally, the modified setup is tested up to load current of 600 A, and uncertainty calculation performed on the measurement results.