Instrument transformers (ITs) play a key role in electrical power systems, facilitating the accurate monitoring and measurement of electrical quantities. They are essential for measurement, protection, and metering in transmission and distribution grids and accurately reducing the grid voltage and current for low-voltage input instrumentation. With the increase in renewable energy sources, electronic converters, and electric vehicles connected to power grids, ITs now face challenging distorted conditions that differ from the nominal ones. The study presented in this paper is a collaborative work between national metrology institutes and universities that analyzes IT performance in measuring distorted voltages and currents in medium-voltage grids under realistic conditions. Both current and voltage measuring transformers are examined, considering influence quantities like the temperature, mechanical vibration, burden, adjacent phases, and proximity effects. The study provides detailed insights into measurement setups and procedures, and it quantifies potential errors arising from IT behavior in measuring distorted signals in the presence of the various considered influence quantities and their combinations. The main findings reveal that the temperature has the most evident impact on the inductive voltage transformer performance, as well as the burden, causing significant changes in ratio error and phase displacement at the lower temperatures. As for low-power ITs, establishing a priori the effects of adjacent phases and proximity on the frequency responses of low-power ITs is a complex matter, because of their different characteristics and construction solutions.

Instrument transformers are largely used to measure voltages and currents in public electricity networks. Their performance is essential for Power Quality measurements. Tests and procedures to estimate the effect of single influence factors are performed according to current standards. However, the instrument transformers are exposed simultaneously to more than one factor. The standardized procedures for their characterization with combined influence factors are under construction in Europe. The work in this paper is focused on the development of a new set-up for the determination of the accuracy and frequency response of medium-voltage transformers within the combined influence factors of temperatures and vibrations. The test set-up includes a platform for the combination of temperature and vibrations, a generating system for harmonics up to 9 kHz superposed with 35 kV, 50 Hz voltage and a reference measuring system. The results of several tests carried out on a 35 kV/100 V/50 Hz voltage transformer in the presence of these influence factors are discussed in this paper. They show that the accuracy and frequency response of the voltage transformers are more influenced by temperature than by vibrations.

The necessity of measuring harmonic emissions between 2 and 150 kHz is outlined by several standard committees and electrical utilities. This paper presents a measurement system and its traceable characterization designed to acquire and analyse voltages up to 230 V and currents up to 100 A with harmonics up to 150 kHz that may occur in smart grids. The uncertainty estimation is carried out and described in detail for both the fundamental and supraharmonics components. From a metrological point of view, ensuring the traceability of current measurements for frequencies higher than 100 kHz and dealing with the complexity of uncertainty determination are bottlenecks related to supraharmonics measurements that this paper proposes an approach to deal with.

Current standard EN 50463-2 indicates the tests and the requirements to be satisfied for an energy measurement system of a traction unit for railway applications. Some of these tests are to be done with several harmonics superposed on the rated voltage, respectively current. However, no calibration systems satisfying the standard requirements were available few years ago. The work performed in the EURAMET project “MyRailS” leads to the development of fictive power sources and reference measurement systems described in this paper. Therefore, it is possible to generate distorted 25 kV-50 Hz voltages with harmonics up to 5 kHz and 90° phase-fired currents up to 500 A with harmonics up to 5 kHz. The generated power is measured by developed traceable reference systems with accuracy better than 0.5%.

Energy efficiency is an important issue in industry, especially with the ever-increasing consumption of electrical energy. The power quality and the traceability of metering devices are essential when integrating energy metering systems for energy efficiency. This management requires an understanding of electrical current events such as pulse and transient currents. Current transducers are widely used to measure these electrical current events up to a few megahertz. Their use makes it possible to measure not only the main current flowing through the transducer, but also the bypass current that affects electrical equipment. Calibration of these sensors up to a few megahertz then becomes an essential step. Currently, most calibration methods are limited to 100 kHz frequency for a current of 10 A. This paper presents an improvement of a traceable calibration methodology for current transducers up to 10 A and 1 MHz, thus increasing, by 10 times, the current level for such high frequency applications. This calibration methodology is based on a metrological traceability chain (uninterrupted link to the International System of Units) with respect to a calculable current shunt and is currently the only traceable method for calibrating current transducers at 10 A and up to 1 MHz. The uncertainty obtained for the transimpedance ratio is less than 0.2%, which is considerably reduced with respect to the existing capabilities.